Motor seems quiet sweet, much quieter as far as top end noise is concerned. I've fitted one of my ignitions on so i can change the timing map, uses the boyer or pazon trigger setup. Wants a sharper advance curve i think. We'll test and set it up at the track in April. Just have to remember to take my laptop.........
No worries, i'll get Matt's wife to video it. I may even take it 'round for a few laps myself if my wife lets me.... It's only a club weekend meet so pretty layed back. It's not as if i'm going to try and win is it????
LOL, I'm reminded of when my brother came up to Nova Scotia to take the Kawasaki High Performance Riding School, at the end of which they held a parade of all the participants. My brother "won" the parade by passing everyone including the parade Marshall. The organizers were p*ssed and they bawled ME out as he was riding my race bike (a lowly CB350 Honda)! I was ecstatic and had to bite my tongue not to tell them where to stick their complaints. After all, he'd obviously succeeded at the finer points of "High Performance Riding!"
Thanks Richard, i found these photos on my phone and remembered that Kevin wanted to see a couple. The exhaust/silencer on it at this time would set the noise meters off as it was a very sharp/harsh note so i put the larger exit bottle shape megga type on which is right on the limit but gets through. It, of course meant considerable carbonation changes.
Do you have just the one breather Nick? I have done the timing chest one like yours, and have one in the centre of the rocker cover, which i think will need a deflector/ guard over it inside the cover, as im getting a fair amount of oil in the catch tank for not many miles, although i doubt the rings are bedded in yet which may contribute. I don't have the timed cam breather in but i have fitted a pipe from the exit into the catch tank for a little extra breathing, also, have you experimented with non-return reed type valves in the breather pipe. Have fond memories of seeing Chris Vincent flying round Mallory on his Bsa outfit, amazing to watch coming down the Elbow with a drift going on.
The primary is used as a plenum the timed breather is blocked off. That 3/8 pipe is the only breather, it seems to work fine. Never used a reed on any of my race engines but all breath into the primary so much larger expansion area.
Mallory was a great circuit, better before the silly 'bus-stop'. Had heaps of fun there.
Mallory was my local track-- I lived about 15 miles away in Rugby. In my early days used to ride there with friends--the ride there was quite fast but the return ride after being inspired by the racing was pretty hairy. My favorite spot to spectate was on the exit from the hairpin--you could see the bikes coming up to the hairpin and the outfits drifting around the hairpin before drifting into the Elbow. Worst sight was when I was spectating from the entrance to the hairpin--Fritz Scheidegger had brake problems and didn't slow down or take the hairpin--went straight on, hit the top wall of the hairpin and was thrown high into the air like a rag doll. Terrible loss as he was a really good rider. Ah well--life goes on!
'75-76 morgo triumph then 90-99 bsa powered always the same old outfit bought in 74. Came here in 99 ran for another couple of years with the beezer. Sold it a couple of years ago now, shoulders and back are a bit knackered. https://imgur.com/ywX7KIT
I still preferred Cadwell Park but only raced on the large circuit once, most of the club and crmc stuff ran on the shortened variant.
Do you have to wait till the club day to test it Nick?
What is it balanced at? Factory tested and found 56% for racing. The Firebird would be 70% and vibes especially in the bars get intrusive at rpm. Though it's smooth up till 4,000 pretty bad by 6,000 or 7,000. Shame the factory never fixed that.
G'day Mark We'll runit up again and pull the head down , do tappets etc before the meeting but we don't really have anywhere to test it and i don't like just running it for long as it needs the rings bedding in.
I took a flyer at 60% and it seems to be quite good, Matt doesn't think it's any worse than the 650 he had before. His passenger thinks it's smoother. You have to consider the fact that most races are so short now the blokes can stand a few vibes. You don't get many 8-10 lap heats with 15 lap finals anymore. In the historic series many of the bikes and a lot of the riders couldn't do it.
Yea, factory said between 55% and 60% made them smoother around 6,000. Bit rougher down low. So after all their work, production stayed 70%. They did all this in the 1950s as well.
It's funny the effort they went confirm what they already knew. Even to drawing and casting OHC heads knowing they could not produce more power, nor be as reliable. When they could have been addressing real improvements worth introducing. Chasing OHC catch up tech, rather than bullet proofing, actual smoothness, discs, 5speeds and hp which would have placed them ahead.
The Firebird has a very sharp sound and a fierceness on full noise that's not normal. I think the clutch is finally just about coping. I cut half the linings off so they are narrower. Having trouble getting the nice valves now because of virus.
I wonder how the factory would have done a 90, still using a bolt on flywheel perhaps?
I have one mostly done just needs counterweights on the flywheel, grinding and rods and balancing and have a 473cam to suit. Reading about the factory just makes me want to try stuff and see what might have been possible.
We had a 90degree 650, big pipes big valves and 38mm TMs it had very good top end, and went from about 5,000-9,000 like a switch when you got to 5,000. It would work at low rpm but not like the 34mm head which is more like having the cake and eating it.
I hope this cam has the outfit going as well as before, or better.
Yep was there Trident Man, standing where the Bus stop is now, I heard the bang then saw Fritz and John Robinson go over the top of the crowd on a built up embankment, Robinson survived, but broke just about every bone he had, The picture is still in my head. I lived 4 miles away at the time, when the wind was in the right direction we could here the engines, it had a certain draw to it, my brother and i would cycle down a Drovers track just following the noise, the chap on the gate would let us in as we didn't have a penny to our names, saw Ago on the MV's, Hailwood on the Four's and Six's, awesome sound.
For a small country we had some amazing choice The old Silverstone, Oulton and Brands full circuit were my favourites. I found Cadwell a bit tight, you had to get it just right or be on the grass, I was chatting with Derek Brindley yesterday and he mentioned that Chris Vincent had a 500 bsa outfit, I didn't realise that, did you ever see it Nick?
Which one????? He won the TT on an A 7 powered outfit. All 16in wheels. I never saw a CV A50 powered outfit but he must have used one at some time. I think i'm a few years younger than you two but i remember my brother in races against Chris Vincent several times in the late 60's early 70's CV was on A65's and the Fath. Brands, Crystal Palace, Thruxton Great choice of circuits back then, a lot are closed now or hardly ever used. Like here, there was a great track here 'Lakeside' they built a bloody housing estate up the road and it's all but closed now something like an 80db sound limit...... all corruption in council and parliament allow it to happen. They are all on the take.
One of my enduring memories of Mallory was the Race of the Year when John Cooper (the local hero) on the triple beat Ago on his GP MV. Must have been about 50,000 people there that day and everyone went totally wild. Good memories!
Mark, I thought i would drop the balance factor down as it's a longer stroke rather than big bore but as the pistons are quite heavy i didn't want to go too far with it. I am sure the cam will improve matters as the previous one was way to hairy for a lower revving motor. It was better with wide tappet settings which is a bit of a 'giveaway' but it hammered like a machine gun when setup that way. As i said the old cam suited the 650 quite well but Matt tends to ride that like it's a 2-stroke. I'm afraid it he did that with that old A10 crank, he may be coming home with the engine in a bucket.
I think the factory may had done a 90 as a 3 piece like norton as it's a much easier way of doing the crank and cheaper to forge. Stroke changes on a 3 piece are more easily accommodated too.
That must be the one Nick, He didn't say A7 or A50 But did mention the TT. Seems like they couldn't get the A50 to work as well as the A65, any stand out reason for that you can think of? They have tried to buy and sell Mallory on several occasions to developers. plus the Noise brigade, you get a moneyed person move into a 50 house village that is encircled by a racetrack and complain about the noise! you couldn't make it up.
Yep, saw that one too. A fantastic spectacle indeed. Apart from the sounds of the exotic foreign machines, the one that should strike a cord for you is the first Transatlantic race's, when all i think 12 where one Bsa or Triumph 3's on open pipes, All 12 in a bunch coming out of Gerrads Nailing the throttle open was a Glorious Sound!
Yes--remember that well---IMHO nothing to beat the sound of a triple on full chat. Even a road triple comes noticeably on the cam at about 4500 rpm. Turns me into a real hooligan for a few seconds/minutes! Makes me forget I am 75 and the Transatlantic Races were 50 years ago.
The big triples ruled the crmc sidecar class in the 90's, they were getting them out to 970cc by stroking them as well as boring. A few were very fast but out of our league cost wise. Then a few guys with imp's would beat them and of course Mr Digby on his big beezer a65. There was also a very quick Saab 750/850 running, that was a lovely outfit, a Lynx frame, beautifully made like most of their stuff. Ahh happy days even if we never won i always reckoned a 4th or 5th against some of those blokes was well worth the ride. Given that my old crate was 25+ years old then.
Nick, I have never quite understood the CRMC, 'they' want to reproduce 'of the period' racing, but allow not 'of the period' engines and modifications - like the oversize triples you detail. I remember in the 80s having a conversation with 'an official' and when asked about thoughts I said overwhelmingly officious and overbearing, he was surprised at my statements! - only changed later when Ian Johnson (spelling!) became involved, more relaxed and friendly with common sense, better grids. Apparently has now gone back to the way it was - pot hunters throwing money at machinery.
PEH, Cadwell is fun because it is so narrow - it demands 'focus'. I remember Dave Hallam on his TZ750 outfit failing to turn right at park corner, the front hub ended up buried in the gearbox.
Oulton Park events are now limited due to newcomers and noise limits. The government refuses to grant 'grandfather rights' to circuits every time they are asked.
Chris Vincent's TT outfit was initially an A7 based engine, he later moved on to BMW engines to go faster. For mainland Open class events he used an A65 engine.
The class i raced in was pre-72 with crmc When i raced in the 70's i used to see and beat a lot of 750 weslakes there were a couple of 850's about but quite rare and unreliable, i never saw a successful trident motor in an outfit at club level then. Likewise never a 900 weslake. That was in '76. When i started with the crmc in the 90's most fast outfits were 900 Norrish motors or big triples, the imps and the Saab were eligible as i remember a fair few of those being about. It was a bit potty really. Mk2 amals, fully dyno'ed and tested motors available etc etc. The club was a bit renowned for being the G50 and Manx club really. It did get better but i just loved the racing, we used to do a few forgotten era meetings with the modern stuff, they were great and used to love to see us. Passengers were always asking to swing on my old crate. They did get a bit shitty if we beat them in the wet though. Over here it was all 1200cc honda 4's in the pre'72 class, i beat a lot of 'em but the attrition rate with motors and gearboxes was huge plus i was getting older and the good circuits are mostly 800+ miles away. The last race but one in the uk i did was '99 at Brands, big meeting several clubs i got a 6th i think. It's actually on utube i think, someone posted it.
Ho ho, oh yes, I well remember my very first race meeting as a competitor on the full circuit at Cadwell on an Easter Monday, nerves just starting while waiting in the collecting area ......and then it started to SNOW, what the...oh they are still going to let us all out on the circuit.......what, are they mad.... oh blimey everyone is going out and going fast, better do the same then, oh well here we go!!! That started years of racing.
At my last race at Snet it was sleeting. That place was cold in July! The wind used to howl around that circuit. When it rained hard they always sent the outfits out for practice first, to dry the track off.
Plum Pudding meeting on Boxing day Mallory Park , The track was white with Frost and ice. The organisers were determined to run the show, They sent a lorry out with 3 blokes spreading salt with shovels then they sent out 2 ambulances to compress the salt into the ice and break it up, Ending up with a track covered in salty slush, about 11 am they sent us out, I was on a brand new Spondon round tube alloy framed Rotax 640 Super Mono. My frame ended up looking like it had been covered in flour, The salt ate the frame, Utter madness, took me 3 days to get it right again, If sweary Bob had seen it he would have took off me, Suffice to say i never did that meeting again. Heavy Snow in the middle of may at a Donnington Park national, They said 15 mins to put your wets on lads, No cover, no Awning, just snow down the back of your leathers, then they sent us out!
I never ever wanted to do the plum pudding meeting, just waaaayyy too cold to be fun on any level. I was never interested in racing before late April/early May, the historic was just impossible to keep warm enough and the 'of the time' modern (TZ750) was a pig to keep at the right temperature. Racing was serious, but still had to be fun and freezing bits off wasn't fun to me!
Nice thing to moan about though Nick!! My historic could not be bump started unless the engine was stinking hot, turn the motor off and it cooled down in a moment, even when the weather was hot. This happened once at Snetterton - of all the places with its uphill start (held at the grid. engines off) and the sodding thing would not start and it was a stinking hot day.
Bloody Snetterton!......i broke a clutch cable there once in practice so i did not complete the required 5 laps to qualify. After some argy-bargy they said i could start at the back of the grid...................... I couldn't even see the bloody start line, and i almost had to turn left when we pushed off! With the tall gearing there, starts were always harder anyway for us plebs with only 4 speeds.
BTW A stinking hot day at Snetterton??????? I've never heard that before!
A stinking hot day at Snetterton??????? I've never heard that before!
Yes, honest early 1980s For me it was either hot or soaking wet
The place was a bogy circuit for me, things only ever down that b***dy straight. Historic - Visit 1 Dropped a valve Visit 2 Snapped a camfollower, which jammed against the rear cam and peeled it open Visit 3 Snapped the crank timing side mainshaft (see visit 2)
Modern Visit # Siezed on No.2 (when flat out) Visit # Puncture Visit # Siezed on No.3 (when flat out)
Just had a good weekend 5 wins from 6 races one 2nd place. BUT.......the old 3rd gear syndrome is setting in .......bloody a65 'boxes! Once the damn thing has jumped out of third once, it stuffs the dogs and will only get worse. The mainshaft second sliding gear is the one that gets stuffed and the ones that are hard to find, close ones anyway.
Is that a 23T Nick? I've had to weld the cam track to fully engage all the gears. You can only adjust the lay shaft to get one good not all without moving the selector with the track adjustment. My friend gave me a ball ended plunger that follows that selector cam and locks the gear, that's in Ben's and is the sweetest changing 4 speed ever.
Who makes the ball plunger Mark? I was think about making a plunger with a 5mm roller rather than the ball, but i would give that a try first. Yes it's the 23t gear. The near unobtainium one! By shunting both shafts in and out i have managed to get the full engagement of the gears using the later better plate shimmed for side play etc. Even so, it has still kicked third out on this one a few times. It may be the fact that he is using an early timing cover with the early small shafted change quadrant, they changed away from those after the first year i think. They were crap, even more so than the later ones. Plus the spring arrangement is rubbish on the early setup. I've told him to save his money and get a 5 speed, he is loosing out off the line to others due to the tall first and no-one ever got those boxes to last in a sidecar. CV told me he replaced most gears every meeting he did. The box was designed for the triumph terrier and just made bigger over the years.
In '69, BSA changed the track in the shifter plate on the singles to more fully engage 3rd gear, at the expense of high gear. But they added a shim behind the mainshaft bearing to move the sleeve gear inward. I have on occasion added another shim on the sleeve gear to force the sleeve gear back towards the sliding gear, as there seems to be a bit more engagement to be had. Obviously, the shifter plate is hardened and it would be difficult to get it just right. Too bad nobody made new shift plates to achieve the same thing on the twins. Tom
I have a 23 I was collecting. For another 4 speed, I had one of the seconds and one of the 1st and need the other two. Ben and Paul's A65s have C/R now and they are so much better. The ball ended plungers do not fit the 5speed apparently. I'll see if I can find out who has them. If you have it out to fix the box definitely fit one. The Firebird doesn't need C/ratios 21-47 is easy to pull in any gear. I still think you should try a head on your thing.
Ben got a pair of 34mm PWKs the other day for under $100.
I have a stock '71 twin carb head I tested the other day because it's actually ported like a '68 Spitfire, though with 30 not 32mm opening. I just compared it to a std 70 port which should be 109cfm, if that's the case the 71 is 122cfm and if they were all like that BSA were on track. A friend in the US did a 13.01 quarter on a 71 with open pipes @ 99mph. He said a '70 was a second slower and the head may be a lot of why?.
A misfire or broken clutch cable can destroy those gears. And I expect the weight of a sidecar and passengers doesn't help. I had 1st jumping out, and it's not very satisfactory on full noise. One of the causes was me, stress, having your foot hovering over the lever and easy to bump, so must kept the toes on the peg till the red light was on, then move it. And keeping the foot away, you have a good millie second after the red
That sliding gear on the lay shaft could go deeper into first with the welded track and the shaft location meant the dogs in the other direction were also fully in. It fixed it.
I once had a couple of gears with rounded dogs built up and recut, they are std and I never used them because I got others. I think they were sprayed with hard facing. They could be undercut so load pulls them together, that's how the 5speed is but neutral needs getting while moving because it's not possible stopped.
I don't know how much heat the gear takes doing the dogs, it may effect hardness if it was really heated? But I don't know what was the case. But good gears with rounded dogs may be worth salvaging. Maybe you could put 'heat ban' on the gear except for the dog area?
I have actually put rake on worn gears dogs before but it goes through the hardening and they burr up very quickly. It was a very laborious process to do, i didn't have them re induction hardened which i should have.
By moving both shafts when you setup the box, you can get full engagement. The two big further improvements to my old outfit were the outrigger and speeding the box up by fitting a 33 tooth engine sprocket. This one has the outrigger but we need to get a 32 tooth engine sprocket sorted out. (33 has to use pre stretched chains)
With a solo, you don't drift around corners on full noise over bumpy tracks pulling twice the weight, you don't spin the wheel up when pulling away etc. Sidecars are very hard on gearboxes and the a65 one was never really a very well engineered unit to start with. It's the reason i was looking at cutting the back of the motor off and using a modified triumph box on my one. It's always the same problem, 2nd and 3rd sliding gears are pushed out of engagement by the torque, this starts the rounding of the very poor dogs and this just gets worse as they are used. Probably a 5 deg back rake would have made the box 80% better but without spending heaps of money, i'll never know. (The unhardened version i did was around 8 degs, it was better but as the dogs were soft it didn't last long.).Starting from scratch the mainshaft should have been 1/4 inch larger in diameter, AMC/triumph type dogs and selector cam plate etc etc. You don't just get a box out of a c15 and make it bigger! The blokes at beezer knew this but they were never going to get it sorted.
Please let me know who makes those plungers, i'll definitely give one a go if you think they are that good, otherwise i'll just fit an old valve spring into the plunger eh?
Do you know why the outfit smokes a bit? Might it have a crack in the JB? A light up the port in the dark with the R/cover would show it. My brothers had a little patch under the valve spring that came out. I fixed it without removing the head and he's had no problem for 6 or so years.
Mark, i fitted a set of rings which i wasn't happy with when i put it back together after morgan park. They had cooked the motor a little there running with a split inlet rubber. I have another set of rings for it, i doubt it's the port leaking as i went through those very thoroughly when i had the head off and valves out.
Ray, i think Baxters is the only place with those gears now but luckily i still have a couple and Bill, the guy who owns the bike has a few. A mainshaft 1st 16t is what i am missing for another spare box.,
Tom there were about 5 revisions to the camplate over the years, the one in this bike is the later stepped one thickest and best cut of all of 'em. Shimming the top or moving the shafts about is all part of setting up the A65 box, i know from bitter experience. Unfortunately i chucked my cut away gearbox section made years ago when i was racing, that was helpful with the setup.
I'm saying nothing about a 16T. Except I'm sort of needing the other one. Do you know what size the motors in the Triumph and Norton are Nick? Watching the videos I can see what's so fun about an outfit, it's a team, and you share the fun and accomplishments.
I started doing another Lightning head. They are pretty easy because they don't break through. It's got std 40.5mm valves but is flowing pretty good. I noticed an interesting thing. I did one port and tested it, kept having to turn the vacuum up to keep it on the test vacuum as I stuffed with it.
If it flows better the vacuum drops because the air goes through easier, but you test at a set pressure. Anyway it got good numbers, I put a stock port on and the thing wouldn't even adjust back enough without opening another air bleed. But I thought I'll see what vacuum is actually needed to pull that much air through the old port and the thing was flat out, heaps more inches of vacuum and it was still reading low. Higher than before but still crap and far below the new port. I probably should have switched the 4th vac on to see if it would do it or pop the circuit breaker. Or just pull the water right up the wall.
I had a thought about this, and what it may be doing, because the Firebird is very interesting. If you increase the total flow of both cylinders enough, the amount of air to burn can approach that of another stock cylinder being added. And how close can that be to having that effect. If the air is travelling at higher speed in quantity it's going to push harder into the cylinder before the inlet valve shuts while the piston is rising on compression. HP is dependent on how much air is in there when it fires. Why blowers are used. Or big displacements, they create more vacuum to pull the air and overlap does the same. It doesn't necessarily need higher rpm to do that because the port is pretty small. A big port doesn't do the same thing because the gas speed is slower and it's inertia is less. Or looking at it another way the boost pressure is less. And up till it runs out of air the more it revs the more it gets. The Firebird also does not ping at all no matter what. A65s with std pistons often can. And maybe the charge enters better?
Matt's passenger had to leave after the first practice session on Saturday so the guy who we press-ganged into swinging had never been on a classic outfit before. He normally passengers on modern outfits. He was lost when they first went out for practice but we showed him how a front exit works and he did his best but struggled moving from left to right. Matt went onto the grass once or twice and had a couple of interesting moments but managed to get in front and stay there most of the time. The triumph is an 840 and the norton is a 920 both on methanol, the vinnie at the back is still a work in progress. I got him to fit an EI and it actually runs now but he has to get the fuel side sorted. I don't understand some blokes, he had never owned a vincent before and he bought this one. He has spent about a zillion dollars on it and it has 1200cc bloody great carbs, methanol etc etc. Why didn't he start from scratch, they produced good power as a standard bike. Surely just put it into lightning trim and start from there?
Lap times were not that brilliant over the weekend by anyone. Matt's were the best but not as fast as he had done before. A last minute change of passenger will do that.
The gas speed thing is important as is the inlet track length as far as cylinder filling goes. Getting good turbulence in the combustion chamber is the way to stop pinging, that can be helped by the way the chamber is filled.
First test of the left port heaps better than the right, and I think I know why. ridiculous with a std 40.5mm valve. Improved conversation quality. Man what have you got done to that! Stock, stock etc, stock valves, just matched the ports to these nice chrome slide 34mm carbs, nearly $100 the pair new. Way too big Man. Yea I know... where's a hill.
In a discussion amongst enthusiasts in popular theory the big things on meths would win hands down. Certainly humorous for us who love our BSAs. What's it like on long straights?
I know Paul enjoys his. He does rallies and things and drones along for hours. Guys on new stuff kind of look down on it, 'What have you been sitting on?' 'No no no they they won't do that!' 'Ha ha' 'The think would blow up'. But they forget they are at the same rally and everyone goes home sometime. And they will be rounded up with the A65 on cruise speed. One guy had a newish Triumph with pipes, sounded great, set up on a dyno 60hp at the wheel. Couldn't match the old thing on hills and big straights still no go.
Matt says it just keeps pulling now, he needs to get a better rear tyre as it's 'lighting up' all the time, off the line especially. Looking at sorting a 16in car wheel and making a hub, that should give him some choice of rubber. It's a fair job as he has to run a drum brake but we'll see. Means making a new swinging arm too. I doubt it will be done for the titles this year but it is on the cards. I have still got 32mm venturis in the carb at the moment, they will go to 33 for the titles, means smaller air correctors with the weber. Still a few improvements to make, but a bit at a time is good. Making sure it holds together is important, seems good so far except the gearbox but i think he's just going to have to live with that like i did. He's found another a10 crank so that's a good move, we'll get it drilled for end feed and a bearing fitted etc. He's got a later t'bolt head which i think he spoke to you about, it's in much better condition than the one that's on there, we'll see about getting it welded up and stubbs put on.
I agree with you, those old bsa things never did much did they?
I was actually interested in what a 650 would do with some rpm.
Balanced to 56% the guys testing balance factors for BSA said it was the best, and smooth around 6,000 but the factory chose to stay with 70% because it wasn't so lumpy down low. Down low means lower frequency which may mean fillings staying in and maybe it's not that bad, not like 7000 at 70% high frequency. If the testers said 56% was better, why not go with it, at least on the Spitfires and get some owner feedback. They just paid specialists to study it with a bunch of engines. Did people really get around at 50mph? Because I do not know any of them. If I knew I was drilling the Firebird in the right place I'd do it through the sump.
If Matt eggs the stubbs and has them a tad lower we can get a bit more out of it, enough that it should be noticeable. Ben's thinking of getting one for his 750 RGV because the carbs are closer together in the limited space and he can use the std RGV fuel tap because there is room. He bought some PWK 34s which are also much lighter on the throttle than the 38tms. And his wrist I think is the main reason.
But if we do that I think he needs to dyno it with the big head first, just to see where it's at.
Always good developing stuff in stages. I don't know if a bolted 90degree would sustain full noise for an extended period but they seem strong. I would not bother with a long stroke just add rpm. I have a map for the crank if you want to try one. There is no shortage of stock cranks.
Maybe with a solo i would agree with you but with an outfit the increased stroke and lower revs makes for increased torque, that gives better drive out of corners and less wheelspin etc. I agree you would be able to happily see a 650 revving to 8 or maybe 9k but to sustain that the flywheel would need to be lighter or the crank would need to be offset. They would break otherwise through flexure. What i would really like is a set of bigger barrels and run 80mm pistons. That setup just suits the engine really well.
I like what he's doing with the smaller motor it makes what he makes it do more special. Like being stuck with a Thunderbolt head, that kind of adds to the whole deal. If he's using around 6,000 56% is supposed to be good there, naturally I haven't tried it, but definitely would if it wasn't such a big job..
I think 80x74 would be the best on a solo and 90 smooth and can rev, though a stock bore and stroke might be more fun. And cheaper. If you want to try a 34mm Lightning head with 34 PWK, around $100, 150 main jets about $20 more, split cable, anytime with changing nothing else just send a head and std valves I'm sure you would be surprised. See if you can figure out why it does what it does. It doesn't have to rev, just feels strong by 3,000 just with a bit of throttle in top, or stronger with more. You don't need to go fast it's just really nice till you hit the vibes. But different bars may be better because there's not a lot in the seat and pegs but the instruments blur.
I could get this finished and make it at least as smooth as an old 3cyl.
The old pommy git seems to have that weber working really nice.
80 x 74 was the nicest version of the engine i ever ran, balanced on edges at around 60%. Back then i just couldn't get enough power out of it, revved to 8k no problem. That's why i would like to do an offset version of that one day. I'm pretty sure now that with help we could get 75bhp from that setup. I could never get more than about 64 in the 90's.
First up though is working with what we have, we need to get a rear tyre with decent rubber sorted. Plus a gearbox that holds together for more than 2 meetings. (something the factory boys never did!)
What you have seems to be working. I guess you know it should make best power around 8,000 probably. If you could get your hands on an A70 crank. If it has a bearing outside the alternator it may help prevent it flexing as well. If you get a piece of wood between two bricks and put your foot on it the ends come up. If you secure the long overhang it is more difficult to bend. My friend runs a 74mm with steel pin with blower on Nitro. For very brief periods.
P4 would allow 80X74 and 744cc if it was solo the 4 speed would last better. A Rickman would allow all round discs and decent front end. It would be hard to beat even with the big inch multies I would think. A modified Rob North style as well if one could weld it up. Ben's got an OIF he wants to run so rear disc is not allowed and it's just more expensive setting up a drum rear, because a stock wheel would be pricy plus limit sprocket choice. So Jap has to be it even though I have a Rickman hub and disk. Available then but not allowed like the forks.
With the early cases there is no solid support for a crank outrigger bearing but i may have a look at doing something. Finding a good A70 crank is very near impossible now, we may as well go to that chap in the 'states who has some A10 suitable for A65 ones on the shelf. They look like a very nice job but they are not cheap and we have to keep this in the realms of reality. If we had a sponsor who was wanting to loose some tax money somewhere things may be different but you have to draw the line somewhere. Running this engine up to 8k would see it lasting very little time, the crank is 50+ years old. (mind you, when it was jumping out of gear last week i think it probably saw over 8k a few times.......)
Not trying to but-in. For mounting an out rigger Brg on these cases, although you never said if it was the original three long stud type! Or the next ones with the alloy bracket. Guess if its the first of them, you could machine a flat on the casing to accept the alloy bracket and allow you to clamp it down to fit the out rigger in place of the alternator. Or (not so good) mount the Brg into the primary cover and make a shouldered crank nut, which slides into the Brg when fitting the primary cover.
Yes John, we have to 'appear' to be abiding by rules so pre 62. The cases are the very early type, a pain but i think we can do something as you say getting the removable carrier to put the bearing mounting in. At the moment i am mulling over fitting the later type gear quadrant with the bigger bearing area, it's a lot better than the original which is just the shaft coming through the timing cover. It means i need to sort out the stops as the early ones used a forked arm onto a peg outside the inner cover. They dropped it quickly as it was pretty bad. He is going to run this 650 engine at the July meeting so i'll get a chance to put a set of decent rings into the 750 and sort the g'box out once i've finished this smaller engine. I used the smaller version of the combination needle race in this one (30mm ID) and it's come up quite well. It does mean you don't have to set end float etc so a little easier to assemble. Blimey, it's nearly May, who said that when you retire time is plentiful.....
Keep chucking your tuppence worth in, it's always valued.
Does Matt want a head for the 650? Or can you use that one? A 650 really interests me because of what the F/bird's like. More rpm should sort of get the same hp from a smaller engine.
I also have a question plenum chambers have a frequency apparently which has an effect. If I put a big box over the head and cyl on my bench it flows a bit more, not normally, but when its near max on 3 vacs. Why? I can see it flows more because the main vacuum drops. Your test vacuum, and that drops when more air goes through and effects vac in the cylinder. It has two big holes in the box for the flow meters. I don't think it reads wrong but makes it flow more, because if you restrict air going in it flows less and the vac goes up. So harmonics in the box or something makes it breath better than with it off and it's obviously not moving just room air?
Maybe a big air box with cold air ducted from the front could enhance it?
I can only think of a plenum/air box being a bit of a pain. But if it was easily put on and off I think you could test it on the bench and see when and if it worked watching the main vac. But it would not tell you what's happening with a running motor which may or may not be important.
Thanks Tom I will look at the links. The sound doesn't work on this so I have to use a different computer.
Mark I have the original head here off the bike, the one that was ported to buggery and cracked. (i'm innocent, it was before my involvement!) After i repaired it and put a couple of plates in the inlet port floors + some guides it was quite good and ran well with the two 32mm mk1's on. Standard valves. The stubbs come out at centres close enough for me to use the weber on it, so i'll do that, just slightly smaller main jets. Matt rides this engine like it's a 2 stroke so i'm happier now i've done the bottom end. I set an ignition up with a rev limit at 8k. for it It does make good power actually, but you do need to rev the old thing to get it. The cam doesn't start working until around 5k but just keeps going. That's how he's blown it up in the past. It's done properly this time with an end feed, big barrel studs, new rods, decent oil pump etc. Should be a nice little engine, with it's 10.5-1's in it.
If you can machine the crankcase to centralise the alternator/out rigger carrier, then you can also increase the OD to allow you to carry larger engine sprockets. Three counter sunk hole to fit the mounting to the crankcase, then another three holes to lock your out rigger into, this way you can give it clearance for the larger sprocket! To make it one piece there is going to be a lot of swarf, so might be a case of make the crankcase mounting and weld the three leg to carry the out rigger on.
I have this Lightning head I'm messing with with a reading of 164.4cfm at std lift and with a stock valve. Only one side, so I need to fix the other and match it, its close. And make manifolds. It may be out a bit but not by much. The stock port smoothed a bit will not go anywhere near it even with 4" of extra vacuum it gets stuck at 135cfm, that would be like a big motor and big cam sucking on it. And hp is burning air. When on the test vac I have to open a vac port because the control doesn't adjust back enough.
If you felt what the Firebird was like you would probably be as excited as me and want to run a stock cam and strengthen the clutch. I do not know how it would compare to the big fire breathing opposition, but really it could possibly be on terms. High comp should help it, I'm not sure about a cam. Cams are about getting additional air at rpm and the thing could have enough for 80hp at lots of unmentionable rpm with a stock cam. But the midrange is great and it needs drive. The vibs suck not the hp. It's got small pipes and stuff but it's ridiculous. Can you imagine the jumping up and down we might be doing if Matt put a 650 first past the flag? If you use the 750 head I could do a better one for it.
I have O/s exhausts in the Firebird as well as inlets. And would suggest that for the 750.
John, yes i see what you mean, i'll look at making up a carrier that is sensibly shaped, or i'll be knee deep in swarf......
How big did you go with the valves Mark, i never really achieved anything by increasing exhaust size, but i was running a bigger cam, that was on my old 880-900 thing. 30 deg seats was a good gain on my original 650. I'll get that head we have welded up and send it down as soon as i get a chance, i'm up to my neck at the moment, i stupidly took on an automation project for an old customer and it keeps growing........ plus i'm trying to get bits sorted for this 650 motor and chivvy Matt into sorting out a rear wheel and tyre etc.
MAP make slightly O/size inlets and exhausts 42mm and 37mm. The std exhaust is 35.8mm so not much difference, but helps on a low seat, and might do something? Same price $30us. They are out of 42mm, which are good with a swirl pattern, I polished one of to see, but the swirl pattern flows a fraction better so Firebird has the one swirl valve in the worst cyl to get them closer.
If you put a bearing out there on a carrier it may mean it can handle high rpm longer. If the 750 can drive past these big outfits or match them maybe a 650 pulling a bit more rpm can as well. 8,000 should be reasonable but with a stock cam the engine isn't peaky just pulls and keeps going, and it's important for it to drive early because there is no risk it 'will' rev. If it's doing what I suspect, it's getting boost, intake forcing in with speed and volume, and size doesn't matter so much. It would be interesting to explore how far that may work, we don't really know. Even with static 9-1 compression, actual cyl pressure may be quite high.
I've worked on a 350chev with a big blower and belt through the bonnet and dual 4 barrels on top, the throttle response just blipping the throttle on the Firebird reminds me of that, it's very sharp and instant. One of the kids does that on the throttle when he's on it, and it can attract the wrong type of attention. I just let it idle without rap rap. Especially in town.
We might find a 650 just cannot do it, but what fun if it can.
Re airboxes,i read somewhere that an effective plenum needs to be around 3 times total cylinder swept volume, out of curiosity I taped up my OIF airbox while it was off, filled it with plastic foam beads, then poured them into a measuring jug, it came to roughly 2.5 litres, so in the ball park for a 750 motor. I am convinced it helps in the low to middrange, certainly better than the previously unfiltered short bell mouths, with no perceptible change at the top end.
If the cam has a large overlap then at lower speeds, you loose a lot of charge out of a carb with no bell mouth or plenum, certainly with short inlet tracks. The splatfire cam has a fair amount of overlap for a road cam, plus with big inlet valves you increase that pumping function. With that engine as you have it, try making a stepped key and retarding the cam by a fraction you will find it's an improvement. Around 1/4-1/3 tooth is all you need. It fiddly to do but a small flat file and a vice is all that's needed. Start with a drive side key.
Yes filing keys, I still have the bolt I cut them from. My main reason was piston valve clearance. Firebird is stock valve timing, it works great. Just think 600 supersports engines make well over 100hp. Maybe a 650 can get around 80 around 8,000 with very decent midrange that the 600 4s lack.
I remember talking to a pair that were at a practice day with with a very nice triumph outfit years ago, they had spent bundles on the engine with hairy cams etc, they could not get the carbs to work with short stubbs on. I suggested trying a couple of coke cans with the tops and bottoms cut out and put on with a couple of jubilee clips...... Voila, instant success, it would actually pull away and drive out or corners without spluttering etc. I think they went away and bought a set of longer bellmouths for it. If it were me i'd have left the coke cans on just to stir the scrutineers up!
I remember talking to a pair that were at a practice day with with a very nice triumph outfit years ago, they had spent bundles on the engine with hairy cams etc, they could not get the carbs to work with short stubbs on. I suggested trying a couple of coke cans with the tops and bottoms cut out and put on with a couple of jubilee clips...... Voila, instant success, it would actually pull away and drive out or corners without spluttering etc. I think they went away and bought a set of longer bellmouths for it. If it were me i'd have left the coke cans on just to stir the scrutineers up!
This is why it's nice to get opinions and ideas from others, some people have a way of thinking outside the box...who'd have thought to strap on Coke cans? I have a brother who is able to almost instantly see such solutions, often makes me think, 'Now why didn't I think of that?' Anyway, he tried a set of 3" velocity stacks on his stock T120 with concentrics (1970's) and said that the bike really came alive (assuming now from midrange and up). Living in a dusty desert, I couldn't see running without air cleaners, I don't think he did for long. The question I ask now is why didn't I try to incorporate velocity stacks into a filtered airbox of some sort? My bike with cams and such may have even been better. And as a teen, I thought a cam had to be degreed exactly to spec, I had no idea I could have advanced my intake cam to close a little earlier to get back some low end that I had lost with the PM 1060's, came on strong above 4500 rpm but with 2 up not so sweet down low. Young and dumb I guess.
Plenum effect is back, if I move the box around over the thing running the vacuum moves up and down, so the effect helps when it crowds the intake a little.
So through the std 40.5mm 152cfm ,about, and 157.3 through the seat opened to the 42mm valve, both with the 34mm carb. If my base calculation is correct. So a stock valve with 34mm carb should perform really well with this port and I will do a head.
I cannot do the 42mm seat properly without the proper guide fitted and K-lined which is annoying. I cut it so I could mark it with blue, but hopefully will be close. The worst thing on these is an automotive cutter to cut 3 angles at once, as the hemi insert then gets cut in with a step to get a top cut, the deeper the worse.
The plenum effect gives 171 with no carb and radiused entry. I guess the more it reads whatever it actually is the better. And it reads consistently and the comparison is good. But now is pulsing a bit. And higher lift is worse than .350" it makes more noise at .388" but doesn't flow more. so maybe the air is leaving an edge and breaking up at higher speed, and its faster but blocked by some turbulence?
Through the carbs it's at least + 45% on stock. I'll take some photos when I change it over for the other side.
These little welded manifolds are round 34mm tube squashed at the head end to be 30mm high and whatever wide the threads are helicoiled to smaller dia for these screws to fit.
They are within 2cfm and one is better further open for some reason. One side broke into a valve spring recess so a patch. The SRM race springs fit shorter so a washer can protect the little patch.
The 42mm valve and 34mm port is up in flow by about 49% through the respective carbs. While I had a stock head in there I tested flow to see what a higher lift cam would do. I did it minus carb so might try it with it. But it went from 109cfm @ .385" to 110.2cfm @ .500". The head flatlines above .385".
Mine flatlines around .350"? So the bottom line is getting more air, so fiddling with more timing and lift will not do much. I ran the 3 vacs flat out, the std head pulls 10" more water to flow 133cfm! But that's not available anyway as it would requite a blower.
The stock head is pretty quiet, the 34 roars and squeals with the carb on. It's 160 through the carbs, probably with plenum effect, and 170 with bell and same deal. It's measuring air going into the box which is over the whole deal, two meters, so I have to read both, but it sucks the box onto the bench and sucks the sides. I tried a couple of test pressures and they are the same within 1 or 2cfm.
So the vacs have to suck much more on the flowed head because air goes through much easier and faster, which drops the vacuum and you measure at the same pressure or vac. If the valve shuts the cleaners eat the water. And the more restrictive the port the more vac you bleed off to get the test setting. The size to flow quantity effects speed, which has energy and that energy is pushing air into the cyl. It seems to do this very well.
Maybe the valve is holding the air against that tight lower turn wall, and as it opens more the air comes away disturbing the flow a bit.
Almost hate to comment since you are so far ahead of me when it comes to this topic but couldn't the increased valve opening also let the flow pull away from the top of combustion chamber that at lower lift is protecting the incoming charge from 'free air pinch'? Something I learned about reading Kevin Camerons stuff. Sure wish you were playing with Triumphs...Mark R.
I have no idea Markster. That valve being there is effecting the air coming in. The rubber plug is from the Thunderbolt head which doesn't suffer that particularly. Ports go flat after a certain lift mostly anyway. But one on this head is worse on one side. If the port floor angles up at all the faster it goes the more it pushes off that turn down. Like a ski jump. I'll have a good look at it this morning.
Not sure what a 406ci chev normally puts out, but with ported alloy dart heads a good manifold and carb can make 692hp at 7200rpm. Lots of stuff makes a difference enabling it but it would not happen without the heads and what they flow. If each inlet flows 400cfm which I doubt, that's 1600cfm per bank, equivalent to the BSA's 160cfm for each port. Dart heads say they can flow over 300cfm per port, how close to 400cfm I don't know.
I also read this; If you’re smart, you’ll begin by looking at a cylinder head’s mid-lift flow numbers instead of the peak flow numbers, since these mid-lift numbers will probably contribute more to overall flow (and power) than the peak flow number.
So through the 34mm carb .250" is giving 136cfm, .300" 155cfm and .350" 160cfm. So it;s probably good this way.
I'm not sure how restrictive a Triumph head is with head bolts, the triples are. Basically for the valve to flow the charge needs to turn down onto it, so lift the floor, but it needs to get around that choke and height is limited so wide is what's left, and can be done if there is space for it and metal.
I wish you could have ridden my outfit before and after i fitted the cam i ended up with. I started with a spitfire and tried about 4 different cams over time. The spitfire always ran out of breath at around 6k with the big engine. That was with a big valve head and reasonable porting, 33mm carb venturis. With the cam it would rev well past anything i ever used it to and would pull a house down in mid range. Max HP jumped with no loss of tractability. Whilst i respect your work on these heads i cannot agree about the performance gains with a better camshaft. My only experience was on the track and lap times were what counted, i never had the head tested for flow etc. I do know that at my last meeting in the UK at Brands, we had a bloody good battle with a 900 weslake and the guy who rode it even commented on how well my old beezer pulled out of corners. The engine was only 820 at that time running t140 pistons.
More lift on my 883 made it better, moved the power up. As an 810 it would pull well to 7500 on the data logger about 55hp as 883 those 38mm ports and 44.5mm valves ran out around 6000-6500, and it died, though it had lots better power while it worked 65hp. Offset rocker buttons added about .020 lift. And it was better. And I was able to get 74hp. It pulled to 7,000. But changing the head made 40cfm difference with the port the same size and it's still pulling at near 8,000 and the guy wanted to give it 1000rpm more to see where the graph went over. I wasn't that curious.
It would be interesting to run it again and see what richening it, and better mufflers did, but I don't want to blow it up doing rpm it will never see. A better cam may make it better, if it was easy to swap and cheap.
It's just I measured the std head and extra lift doesn't do much, but different heads can act differently how they respond. And duration makes a difference.
From what I've seen the A65 stock motor isn't restricted by the cam so much as the head. It's not a direct relation ship between cam spec and rpm levels when cylinder head flow is changed appreciably. More air allows higher rpm. If the head is at a good place, then testing cams can show what spec works best.
Why I'm interested in the difference between how the current rig goes with the two different cams. Is one noticeably better? And it's not particularly peak hp but drive.
I'm thinking I should give the Firebird a short dyno and hope the mixture is close and it stays together. It's not like I don't test it on the road but it makes me nervous. Like going home, Deb where's the bike? I need the trailer and degreaser. Should get Ben to take it up.
The head on the 883 didn't make much difference in the mid range, the Firebird feels different from when you take off. And seems to totally transform it in a 650cc kind of way. And it's hard to quantify without a stock one to compare, so I need some sort of test. The SV is out of rego so I cannot do rollons with that which would be easy.
With an 89mm stroke i was never game to use 8k rpm. I would have visions of tops coming off pistons etc. Plus lower rpm gearchanges seemed to give better lap times. When the last motor i had was on the dyno with 80 x 89 it was getting 80hp+ at 6800-7000 it didn't get much better at 7.2k which was my maximum. It had B44 slipper pistons in it then. It's not an easy thing to get a sidecar on a dyno here i've found, the shops don't want to know. To much trouble to fit it on etc. Using those offset rocker arm things is not a great idea i was told, they have a habit of breaking off.
Like so many of these things, testing the bike is a problem up here, there are no practice days anymore, so if i try something it must work first time....... Or the weekend racing is stuffed. Back in the uk, Mallory Park was open every Wednesday PM for bikes, we got 10mins in each hour for sidecars. Plus most clubs had practice days prior to meetings at the circuit. It's a bloody long trip to go down south to test the old crate as all our circuits (3 of 'em!) are shut or booked solid.
I have JE forged pistons and good ring pack, they are not the worry, it's everything else.
Trivia for tonight. I started doing a head to run std valves. I will call it head X. So I made manifolds first so I could line them up. I want the floor to run in one sweep over onto the valve, being straight is ok, but if going up the the air wants to continue, if it starts to curve down it might follow the sharpening turn once it has started. So I traced through the manifold with a scribe to hack out the oval, then hacked out the sides of the guide area and bowl then joined them up checking where the manifold aimed and where the floor would be.
So put the manifold on, a valve and loose guide in, and tested with calibration from the stock head. Of interest full vac on the stock head was pulling 6" more vac than X. Stock 109cfm, and through the X, 34 carb is 142cfm, 148 with a bell on test pressure. So on track and the floor is now setting.
Interesting trivia, I reduced the test vac on X without carb or bell by 4" and it's still flowing 126cfm (instead of 141), which means that at lower rpm making less vac the head is still flowing more air and the motor will make more power, 17cfm is quite noticeable. When the port is done, I'll check that again with the finished port size, which is smaller. Smaller effects speed which effects how it pushes in. It wants speed and air volume not one or the other.
Should get club rego Nick. Just need some lights. Only a pink slip here. 60 days for testing, just fill out a log and go. Or go on club runs. You might have to turn back if you're run is to Cairns. Just say it was getting late or something, so going home. They can check if there was a run and you are fine, if you are not on slicks. And you have always got, slicks were allowed on the isle of Man. Don't wear patches. Probably get busted for wearing 'Sons of Arthritis' up there.
This is the starting point and I think it's the better '71:
And on the left, it's wider and deeper in the bowl than earlier heads and about as good as the better of the Commando stock heads. See how it's narrow at the guide where the guide obstructs flow. The one on the right is the exact same size with 30mm hole but flows 143 or so. A 650 doesn't need them that little.
Place in Melbourne done once and no problem. Place in Qld is much cheaper, however it came off twice and the second time destroyed the piston, so cheaper to pay more the first time in Melbourne than twice plus piston.
John Hill in the UK does alloy cyls and Nicasil bores to your piston size. It's more expensive to machine and have bores done here. A JE forged piston can run .002" mine are .0025". I've not tried the 76mm A65-70 pistons EdV does from JE, Just 79.5 and 80mm B44. They work great with the long stroke because the skirts are short. They really need longer rods. I had a taller alloy block cast but never used it.
This is a sketch of the XR750 port. So I'm trying to improve the bottom turn and make everything smooth. And stop break aways and turbulence, the turbulence I think it needs is entering the cylinder and its what it is.
Humming and harring about doing a big motor with the norton crank i have here. Couple of options really, make it 90deg (never tried 90, used 68 +76+180) have the crank ground down to A65 size then he can use his map rods with it, or it means corrillo's. Big cost these days. Seems a shame as the crank is standard and would dress up at +10. Just mulling it all over at the moment. If he uses his rods i can have the crank ground to give 90mm stroke. Another option.
Ideally 80x74. Or 80X89. And 90degree. Map do long rods for Nortons and for those cranks in Triumphs. But they have a smaller pin. But bigger bolts I'd expect. JE will do custom piston sets in 4s I think. You could use B44 spec modified. You could try the pin higher in the piston, or longer cylinder. They need long rods to cut down the side thrust at rpm and vibration.
80x74 lets it rev. In theory the 34mm head may see 90-100hp and pull hard in the midrange with 744cc but it may need biasing a bit for top end with bigger dia headers. It depends what that size head supports, and what it does. The idea that the opposition use big bore engines might mean you can as well. If they say Devimead didn't produce them till later, I made mine, made a pattern and had it cast. Anyone with a back yard could have done that.
An 80X74 could be 360 if its balanced and is ok till 8000 or a bit more. The bigger bore will breath better and you could go bigger valve and carb size. That XR750 port is huge but they pullover 9,000 and wear out. I couldn't fit all the XR port in the BSA head. It's 49mm wide, I could only get 43mm but I'm sure the big motor could get 100hp if it would stay together. I had 8mm head bolts now 9mm and the back has 10mm. Because it was pulling the threads out. It ran fine on 12-1 on 98 but piston to valve was pretty close. It was 11-1 when I dynoed it. 12-1 and correct mixture might have meant degreasing the dyno room.
12-1 gave unreal response from the big thing, I thought it was about 10-1 till the platting failed and I measured the good side.
A 12-1 744 might do the job. I know bigger can have more torque in theory, conventional theory, which I'm starting to think is questionable. Have you seen that video Matt has on his page of Asians in sandshoes and jeans drag racing little strokers with almost pushbike tyres doing 10 second quarters? I think one did 10.6 and nearly 200kmh. Like a pushbike with lawn mower motor and chamber almost.
I did this head for Chris in the US. I don't think he's run it yet. His bike had an A10 crank, high comp and had a stock 71 head except for 34mm TMs, if I remember right, a LSR and very fast. It made 60hp on the dyno, around 68 at the crank. It would be interesting to see what it dynos with this head. It looked really nice.
This was experimenting with a round 32mm entry. The X head is off this scale .300" is over 165 and .350" over 172 what ever that actually is. And I expect it's wrong, but under the same conditions and comparable.
Putting hp graphs overlaid like this would be interesting. I put the calculators figures on the right. But it's power curve that's so important.
So overlaid dyno graphs would tell us a lot.
The calculator has settings of how hot the motor is to get 68hp. With 110cfm it needs the super hot 'pro-stock setting,' which predicts 65hp, a bit less than the reality. But I think the rpms are right around 6,000, no more after that. So with 160cfm that same setting gets 94hp? It's rpm range predicted is above 7,800 though. On the milder race engine setting if it actually had 122cfm, which I checked a 71 head close to lately, then at 160 it would be 84hp. Still at higher rpm. Why using an 80X74 might be better. That's allowing a bit for the head to be over reading. But the 34mm head on a 750 could be right in the ball park, as it seems to be on the 650 at the rpm you can hold onto the bars. Even with lower comp and stock pipes.
We are hoping to see Chris this year. I did the dyno work with him and was really amazed at the numbers we saw at only 6k. With your head it should make some serious record breaking horsepower.. PRT PS, His bike is beautiful!
I hope it goes good for him. If he dynoes it, it would be most interesting to compare graphs. That bike is very photogenic.
I think this is Chris's graph I drew on tests done by a US magazine around 1969 or1970. RWHP to convert to crank hp as used by factories times by 1.1343.
You can see the advantage or not of marketing by the factories. Lots of people loved to be able to say their bike was the most powerful. But manufacture created variation as did preparation, though these would have been to factory settings. The Trident was a good one and maybe the Honda wasn't.
This is my 883 on the same graph. Different dynos but sort of comparable. The BSA would have been better at lower rpm without being on full throttle. The first run read 85 on the screen but the rpm trace was messing up. Which doesn't effect the reading at the drum but was meant to control rpm which it didn't. I was told not to worry about these readings it was way too lean. But this is breathing influencing where the graphs go. Lots of components influence that to make the best use of the breathing you have.
Mark P., when starting as a line boy (1970) at a Honda/Triumph dealership, if someone wanted to take a test ride on the CB750 we would go along on the Trident as we knew we could always catch them.. just my experience so maybe your graph is fairly representative of a typical Trident or Honda of the day. Mark R.
Except Chris's graph is from dynoing with the std '71 head with 34mm TM carbs. Not the ported one. Which I'd like to see when and if he tests it.
BSA tested a race engine in 1970 with A10 crank and 34mm carbs at 78hp @ 7000, power was falling by 7500 to 77hp. Really nice power curve. They put F750 3 tests on the same graph revving past 9500 trying to match it, which they almost did. A tuned 654 was kicking the 3s butt till about 6500. Why dynoing a 654 with this head might be interesting.
So where that head does its best I don't know. But I know the A10 crank problem. Maybe an outrigger bearing may allow more safe rpm? Or better safety for what rpm you run.
I emailed Gary from SRM. He was saying a customer dynoed his road 750 80X74 with 68rwhp using their race cam and ported head. That's around 77hp at the crank.
He is very enthusiastic about their race cam, saying they tested many cams in their outfit to arrive at it. He's also enthusiastic about a 90degree and the extra torque they produce. And loves what you are doing. With the most underrated British twin ever. He left SRM recently, but said they have a couple of their race cams for 90degree engines.
Comparing the flow of a stock head to one I'm doing with stock valve, I can turn the vac down by 7"w and it still flows 16cfm better than stock. Which means bottom end and midrange should be better, as with response as it turns more air on whatever rpm you open the throttle I expect. So it's a bit weird. A plate near the air intake flows a little better till it sucks it on. You have about 1/4 of a second before the vacs eat water. I extended the hose toward the roof before it loops over.
Pretty much finished that port. Std 40.5mm valve flows really well. Still has a 34mm manifold at the other end. The difference between stock and ported is about 9"w if that means anything to anyone, That's with 3 vacs flat out pulling max vacuum on one then the other, the stock one is that much more restricted or choked, through the exact same valve. If my measuring gear is a bit sus this difference isn't. Its pretty unconventional wisdom that you can get so much more air through a std valve on a port that isn't much bigger. It make you wonder if it can work. .
Yes, the SRM cam is not a typically radical cam, in fact it's milder than many 'street' type cams around. The quietening ramps are very effective too. With that in my old 730 thing (79x74) i achieved 64hp @ around 7500 That was the best i could get with that engine back then. It had a pair of those nucleas valves, standard size in it with the weber at 33mm and long trumpets. The short large radius type may have improved it a bit. That was the sweetest and most reliable of my racing engines, revved to 8k no problem, started easily, was quiet, relatively smooth, just 20hp light!
Gary must have retired by now surely? i used to speak to him back in the 90's i doubt if he remembers me though as we were never quick like Stuart D. He dug out some CR gears for me back then when they were hard to get. Over the years i bought a lot of stuff from SRM, 750 kit and two 850 kits the last 850 kit was very good the casting and material was really nice that was in about 2000. They were always a good outfit to deal with as the blokes had 'been there and done it'.
At the moment we are looking at the gearbox problem and sorting out speeding it up and then i can address the crank outrigger, i'll have to make up some sort of structure to support the bearing as with a bigger sprocket i can't easily access the existing tapped holes for the alternator supports. I'm working on it, as they say. Putting a small needle race on the change shaft has made the horrible early mechanism around 250% better, so i'm pleased with that. It'll probably wear the shaft a bit in time but we'll see. I put a small o-ring in there as well to seal it.
BTW, we have another A10 crank, maybe a 90 deg version of that eh? Another option.
I have a flywheel centre machined up. I don't think is has bolt holes. It was a spare. And I have the last crank I had cut together because I might put it in the Firebird. I don't know exactly how strong they are, other than they are extremely tough to cut. There are lots of nuts and bolts and locktite. I tell myself the flange is bigger diameter than a Norton with more bolts plus the big ones up the pins. I advanced the left cyl, SRM the right, so it needs doing their way to suit their cam.
I think Gary only just left. They port heads and use nice machines and have a flow bench, but have never used it? And he doubts anyone there will use it.
I have a map we gave the machinest to cut the crank and bolt it up, I'll see if I can find it.
This may be interesting, This is fit the cylinders easily on your own. Advantages, the block sits on a piece of wood and gravity stops the followers falling out. The pistons are already fitted in the bores and hanging out the bottom with inner clips in, fit pins at your leisure and clips. Check about 7 times each. 90 degree doesn't matter, put sealer on the joint, check followers, slide it on.
This is the first cyl I made with thin liners. I flogged it for years. The pistons were cast and had low skirts that came out the bottom a bit, It cracked a liner. So I then used Nicasil and pistons that fitted properly. I regarded this cyl scrap. I practiced tapping the threads oversize. Drilling the old holes bigger using a very quarely set up press was no good. It was not accurate. Holding between feet and drilling straight down meant you could feel the hole and get them exact, It didn't matter, it was practice and just scrap. Have another set machined almost ready to Nikasil$$$ for Bens 750. But I had a liner and it could be replaced and bored pretty cheap. And we had Pauls old 79.5 pistons done a million miles but sort of ok.
There are reasons not to but it was cheap the holes had threads and were straight enough to get bolts in. What's not good is liners can turn, doesn't matter on a short stroke because there is no cut out for the rods.
A hot rod 750 would need 9mm bolts, 8mm would pull out, even in Iron they may be a problem. Though if you used an iron block you could wait and see. They are reduced. Std are just under 10mm in pommy thread and distort the bore. The 9mm is rare but used in some VWs I think.
This graph is for reference, it's a hot XS650. Stock is around 43rwhp like A65s, this lists what it has with the 750 big bore kit. Fairly close to the A65 750 Gary was talking about. But the aim would be getting as near to 80rwhp as possible with a very strong midrange.
Did the second port on the std size valve head. Before putting filler in, I compared it to the stock one just running 3 vacs on full, stock pulls 9" more water in comparison. It's a fair bit of extra air but I think it's better hitting the valve from the back and being smaller and faster.
Goodness knows what a stock A65 would go like with this head. It shouldn't be much behind the heads with 42mm valves. If BSA made them like this the stock clutch would not be good enough.
This is Ben's head, the valves are 44.5mm like in mine. Mine though I lifted the valve guides and stuff. But really for that size valve it could probably flow 230cfm, not 200, and 200 is more than the 883 can use, Ben's is around 190. Better than an 8V modern Triumph head. But the thing is, the port and valve is probably bigger than required. I'm not sure what a 42mm can actually flow, if I make the port a bit wider. On mine it was out between the fins and higher. Numbers at speed mean more than just numbers. Yamaha spent millions on an XS head just for flat track, it made their 750 engines around 100hp.
We are hoping to see Chris this year. I did the dyno work with him and was really amazed at the numbers we saw at only 6k. With your head it should make some serious record breaking horsepower.. PRT PS, His bike is beautiful!
Hoping to see Tom and Mike this summer for some well over due tuning, the A65 LSR Lightning is sitting right up front starring me in the face when I enter my shop. I wouldnt be surprised if the 34mm carbs will need to be replaced with larger ones. As soon as I finish up a Victor I'm working on the Race bike is on the lift to check compression after sitting for a few yrs, change the oils and fingers crossed, fire her up.
Firebird's original head, stock valves and ported to 34mm PWKs.
This is interesting because I tested side by side with a stock head using the same valve, 40.5mm. I assume the stock head is 109cfm minus carb. With carb then 106.5cfm. The ported head is 155cfm through the 34mm carb and same valve. Or some where near it. 45.5% approximately more air. And importantly much faster. And in the Wallace hp calculator for hp based on flow about 45.5% more powerful. Std 106.5 works out at around 50hp. On their mildest spec Street/strip. High comp, 11 or 12-1 should put it in race motor mode and hp estimation. It would be interesting to see. 750cc brings rpm down.
The 42mm valves are about plus 50% through the 34mm carb.
This shows ports at stock valve size, stock 40.5mm valve, 42mm and 44.5mm.
So the oddity. The std valve with 34mm carbs now flows just as well as the 42mm valve version. Testing back to back. Both work out 49% increase in flow over the stock one I tested them against.
I got some really nice sanding red strips yesterday. I had almost polished the ports chasing flow with wet and dry in the die grinder. But they were not without little bumps and marks, so I used the fine red strips in it to get most out, it left a sort of sheen and improved them both. So it should be the same as my Thunderbolt head on a bike.
It means O/size valves are not necessary on a 650 or 750 to get it nice. My friend is building a drag bike, possibly a big bore 750. It would be a good test.
I don't know. The port size is virtually the same with 42mm, it's not much bigger than stock. The length can add cc but the cross section is what's important. It determines speed. Stock is slow because air cannot get through. Stock ports don't look normal to me anymore. If they had a cast manifold I could hand do these pretty fast and get most of the flow straight up. Especially on a head without the std port. And those carb bolt holes could be moved out a bit. They may have been able to cast the shape a bit. But it's a bit like art doing it by hand. Machines could do it today.
I didn't think this was possible with a std valve. I am totally amazed. But I think that means the 42 can do more and it may be better at low lifts. They cost the same about $30us
You know we had a boat when we were kids ski racing. We won lots of races especially drags. Because I was light and out of the water fast. The thing did 60mph and it had an old Y block 292 ford with twin carbs, probably made 220hp maybe. Yet they now have small blocks with pushrods, single 4 barrels around 1,000hp with no blower.
And it's the heads and airflow. 4 valves might be great but it's a hemi drag engine they estimate at 11,000hp. Because they do not make dynos for that.
If you can get good weld in the tunnel we can see. Because the Thunderbolt is a really good head.
What's ironic is BSA management 'thought' they needed dohc engines to catch up. Yet they could have had a light, cheap to manufacture 750 pushrod twin, with more grunt and top end than a Z900. If they solved the vibes. Tony Price showed what they would do as a solo.
Well big valves for this one. I put the good guides back in and by the time I got the seats again they were down a bit. So I have one port very good, better than ever, but not the other. It's deeper so I'll try matching it. It's about 3mm shallow. I've been chasing this around trying to match theory to reality. It's about 7 or 8cfm different. Big plenum effect on it probably 8cfm if you could get that right on an outfit and jet for it. None on the std head or at low lifts. The plenum effect pulls the main vac down, so it increases flow.
This is the best port so far.
The two black dots represent the biggest difference. I'll see what a couple of mill more depth does on the right one but nothing is guaranteed. I also need to open the seat a little as it's a bit wide still. Just the curves or little lumps make a difference. Left to right is 174 and 167 with the radiused edge on the port and that plenum effect. If you were a manufacturer, developing a plenum would be worth doing.
Pictures show how different it is.
I've been reading some interesting stuff. The ideal valve size for a Hemi intake is .57% of the bore size. So for a 650 or 750 A65 with stock bore the 42mm is .56%.
For an 80mm bore 44.5mm is .556%. Then there is air speed in the port. For a 750 with 44.5mm valve it needs rpm because it needs the speed.
@ .637mach the volumetric efficiency is 127% @ .55mach it's 121%
300fps is ideal. Though 614fps is possible with a good flowing port.
A late closing inlet makes best use of this flow speed 60-80degrees abdc they say, other valve timings events are less important. Std is pretty good at 68degrees,but retarded a little is still in that range and the 473 gives better piston to valve clearance retarded. The more speed in the port the more it can use that later closing, gaining hp not loosing. As, if it is shut with more air under high kinetic energy trying to force in, it's wasting hp. Hotter grinds can have that later closing. Though exactly where that is is probably by experiment. That piston to valve clearance is important because it needs more to breath than to just miss.
A map Nick. But the timing side needs to be leading, so drive side crankpin is retarded 90 degrees. Then the SRM cams suit. The first crank has an oil slot the second a wide groove, like the one I'm doing. The counterweights are bolted on which isn't on this drawing. I think the f/wheel is the same dia as the std crank. I think we used 8mm bolts not 9mm.
To quote Gary; 'The 90 crank engine will produce insane torque for its size, well worth doing.'
Ben's is dynamically balanced around 50%. High rpm may be smoother if its around 47% but I haven't tried it.
Yes, thanks Mark, i like the 90 deg standard crank approach as it is strong and would give plenty of poke with an 80mm bore. In all honesty, the bike would struggle with much more power than that anyway. I still think 75 at the back wheel is the aiming point. We can then work on getting corner speeds up etc knowing we have a reliable engine package. I obtained a 32 tooth duplex sprocket the other day so will start to sort that. The crank outrigger may be a bit strange though, i'm thinking of just bolting it through the front, top, bottom of the actual case rather than standing it up from the base of the case. I think that will be stronger and less flexing.
It would be interesting to know what hp the A65 has now. They run a 920 Norton on methanol in a NZ outfit measuring 98hp at the wheel? Is that one up there not breathing well? It obviously may not have that output but it must have a good bit. The BSA possibly needs 7500 to give it's best in a catch 22 situation. The extra bearing may help but it's really an unknown. If you use one on a 90 you can use a cheaper NKIS30 in the timing side. You can get them in a C3.
We'll never be up at that Mark. To get those nortons that big etc they use nothing which is norton virtually. The cases are about an inch thick, corrillo's, 1 piece special cranks, fullauto heads etc etc. It was a bit like we were chasing weslakes, you may get there sometimes but not often. Plus the attrician and wear rate is very high as are costs of doing it. I'm adamant about the rev limit with the A10 crank, 6850 is it, no more. Piston speed becomes an issue much beyond that as well as the actual crank strength. The thing is going well and he gets heaps of fun out of it as a reliable (except for the gearbox) bike. If he wins the lottery things may change but i've enough experience of stretching these things to know where the feasible limits are. The 740 engine uses a standard needle race 30x 47x 22mm not the nkib The 650 uses the nk1b. He will be running the 650 at the next meeting so it is 'run-in' as his spare for the titles. That will give me a chance to get the 740 ready, outrigger, bigger sprocket new rings, gearbox etc. It would be great to do some dyno time but finding one that will run an outfit is hard.
That comment is in relationship to what the BSA may already produce. If you can beat a 920. Not suggesting he uses 7500, it needs to be reliable, but just that it may make more power there if he could. And why a big bore may be more usable. You can see that graph of Chris's, his similar configuration makes massive power at mid rpm, that's very valuable. You could possibly have that with more up top I would speculate. And I'd for sure use a 650 and see how that went. A 650 can easily grow to 744.
The reason I drew Chris's power curve on the graph is just how good it is. It's not what people expect. I had my 883 on one side of a car dyno. We have had a Toyota turbo diesel on it with about the same.
At the moment i would take a guess that it's chasing 68hp at the back wheel. It was down on that when it last ran as it was smoking and compression was a little down. Yes the 650 can grow to 750, we are looking at a crank at the moment for cutting. I am seeing Matt today so i'll go through a few things with him. Ask about dyno time etc.
If you are bolting the crank I found a long philips head, the correct dia, through the 3 sections can be lined up with the crank, you can put it through a couple of holes and it trues it as it gives leverage. Just get it in line with the ends of the crank.
The 73 works Nortons were 67 at the wheel and 76 at the crank as they tested on both engine and rear wheel dynos. The best works 3 tested in the states was 73 at the wheel. But that is a peaky engine, not like these twins.
Just buttoned up his 650, put a needle race on the gearchange shaft and it's excellent. Have made a rounded chisel shaped index plunger for the 740 motor am going to experiment with that for the fun of it..... Not bothered about light gearchange action, just want the damn thing to stay in gears when selected. Especially on this one as it's my gearbox he's going to use. It's funny really as the inner cover is about a 1/16 out of line with the actual gearbox end plate, no wonder the change is so crap on the early ones. we trued it up when machining for the needle race and drilled the outer cover to 15mm to get clearance. Should be a nice little motor with all the odds and sods we've done.
Looking at it and reading on this wet afternoon the std dia exhaust valve may be good with the bigger inlets. The more compression it has the smaller the exhaust valve can be in relationship as well. I have an old head I might experiment with and close down the inlet port to 34mm using a 44.5mm valve and see what it does. Or can do. The bigger valve diameter will give greater low lift flow. And may rip a bit more air through a 34mm carb if I can make the little port work. Suiting an 80X74 engine. The 42mm works great in a 75-76mm bore. I could cut an old valve down to 43.5mm (SRM have good ones that size but they are 61pound a pair) and see but I don't want to stuff a good head. Then again I have a 71 with a broken rocker shaft post.
I'll buy some tube and test gas speed in the port as well.
High comp pistons in the 75mm chamber can mask valves more so than a big bore. Vizard blends the lip of the valve cut out so it doesn't block flow at TDC toward the cylinder wall. I usually blend that to take the sharp edge off. A bigger bore and or a longer stroke can leave a more open chamber. And 12-1 is not unrealistic maybe.
This seems about the limit through a 34mm carb and port at the moment with the 42mm valve. So a bigger valve may improve on it. And getting an idea of speed would be good. It can be that a large port is so much slower the engine doesn't even get as much air. Or you wait forever for it to kick in.
So with the 34mm manifold and pwk carb on a big 44.5mm valve head, flow maxes out at 177cfm. This manifold doesn't fit right as the top of it is blocked. It's just a matter of doing a head where it lines up properly and making the port all the correct size and shape. At the moment through that 34mm manifold with radiused entry it's 191.3cfm, a bigger carb will not loose so much but a bigger port loses response.
It looks like making a head with the 44.5mm inlet and 34mm port could be lots of fun, if it can retain the midrange response, and I do not see why not. Low lift flow isn't quite there yet but the seat and port can be better. I need 4 vacs going to test this and higher test pressure. It's just flow calculated from testing a std head. The smaller valves are perfect for stock sized or long stroke motors, but this may be the thing for a big bore 750 race motor when you want strong midrange drive and don't want to exceed 9,000 particularly. It might actually be that carb and port size do not give much more flow than smaller which increases speed and power. I've run my 883 on the dyno once and had a best of 85hp at the wheel and lots of pulls around 83hp but adjusted nothing because the main jets were so lean. So I don't really know what is possible for that big motor, in Vizard's book he talks about getting a motor to finally give 145hp on a dyno and then spending 3hrs fiddling with it to get 170hp. So maybe 95 at the rear wheel is possible with the 883 set up right, if it stayed together and if there was any point.
Problem is I only have a couple of good valves. Which are cut down nitrided Jaguar that I don't seem to be able to get any more. Valve seats need to be central to get these to fit as well, but I think it's worth doing on a 750big bore with lots of compression and a cam. The idea is to make good hp to 7500 and be able to use more at higher rpm if necessary.
Just to add later T/bolts with 40.5mm valves have larger inlet seats so don't need the expense of fitting new seats.
Edit; looking at the seat it's very ordinary but making a better fitting manifold gives a better idea of what is possible. Through the carb at .428" 180.5 .385 178 .350 174 .300 162 if that stays close and is anywhere near accurate, on a finished 34mm port it would be devastating. A 38mm carb and port is only 184 so unless that was increased it's no advantage probably a loss.
The valve is holding the 34mm tube that is squashed oval at the head in place jammed against the cap screws. This head on an RGV needs curved manifolds so Ben is looking for a good Thunderbolt head.
From Vizard's book a std 35.8mm exhaust valve is a close match to a 44.5mm inlet in a 9.5 to 12-1 engine for best power. MAP have 2X B50 44.45mm black diamond swirl valves $40us each.
Do you know what lift @ the valve the SRM cam has Nick?
I clocked it at around 410 thou at standard clearances maybe a little more. The cam is around 370 over base. Timing figures actually line up quite well with their spec in 45-78 ex 81-45. @20 clearance. The cam in this 650 has less lift around 340 over base, gives around 370 at valve. in 50-70 ex 80-40 @20. I suspect it's a little worn now but still works well. Maybe could be retarded a fraction. There is bags of piston clearance compared to my old outfit with both cams. How much crush on the inlet tubes?
The inlet tubes need to be lower and lined up with the port and squashed at where they meet the head so they are about 30mm high and about 37mm wide or whatever. If they are high they aim down when they need to be straight or curve over rather than go back up. It's only a slight difference and making them oval helps. The std port is 27mm so that may also be ok. The port at the top needs to go straight then over and down, it's compromised if it goes down and up to clear the spring area.
I'm excited about this, I didn't know this was possible with the 44.5 valve. SRM's 43.5 would be good as well. I have 3 good heads done for 42mm valves and am tempted to do one to the bigger valve. But I think I'll just fill the bigger port to match the 34 manifold properly and try not to lose anything.
The stock cam lifts the valve .385" the rockers are offset.
This is my one it ended up a little wider I think but if you can get some weld down that thin edge it would be good. 30X37 or so,
This head I'm messing with I started filling the big port tying to get 200 out of a smaller port but was having a lack of success and left it. But with the smaller carb and manifold it becomes something quite different. I measured the port volume to the gasket face to compare to the 42mm valve port even though I will be filling this more, it's 75cc, the 42mm valve port is 68cc 10% different.
About 70% more air through the carb than the stock head rather than 50% for the 42. The stock port I think is 63cc, I'll have to measure one. I'd guess fixed the big one will be 71-72cc. So around 16% larger port with 70% more flow. And so much more speed when it does it. Generally flow increases are not on that scale nor without big increases in port size.
This is from Vizard's porting book. He used a small port Dart head he ported and fitted a bigger intake valve + 4% the flow was up 8% and port volume +3% it's the redline. They also tested a bigger port Dart head with that bigger valve, against stock and std small Dart head. The bigger port isn't winning because it's slower and would be better on a bigger engine. He also gave it more compression. From about 9 to 10-1.
This is a really good illustration, the black line is the exact same engine with stock breathing heads, what's changed is cfm through ports and a little extra compression on the red trace. And it's not even a Hemi with its much higher potential. The A65 doesn't need a different casting.
The graph shows the relationships of flow with different ports and valves, the numbers might not translate exactly, but is the comparison. The red trace is through a 34mm PWK and 34 manifold transitioning to oval and 44.5mm valve. It's likely more flow than needed for a 650, but may be good on a 744 or bigger. I may yet be able to improve it a bit but it gives a basic achievable level. It's not a go for broke port because it's hoping to boost gas speed and midrange as well as top end, and not break through. It measures the same replacing the carb with a radiused entry up until .200" valve lift, then it's the black line.
The green line is with 42mm valve through the same 34mm carb.
The std port without carb, then with a 30mm Amal is down the page.
Flow through a 34 Lectron would not lose so much as the PWK, but price difference is major.
Port volume looks around 74cc. It's bigger but it flows more per it's volume increase than the smaller, if the engine creates the vacuum. Both should push rpm of respective engines to 9,000 or more if required.
Time to set up a manometer to measure speed in the ports. Even a comparison would be good. Because speed is energy and cylinder packing.
I have the stuff to make up a manometer to measure air velocity in the port. But need the test pressure right on 28"w. Then you put the tube of the velocity manometer in the port and see what vac it pulls. That vac then converts into feet per second. It should be interesting with stock, then the two 34mm ports.
This shows how small the entry is with the 44.5mm valve cylinder head. The fill is in the top and bottom and you can see the port is made lower from where the cap screws are. It's going to be fast through the carb and manifold.
This old head has big exhaust valves. From what I read they are over optimum size. That relates to compression and cam timing, higher comp and longer exhaust timing goes together with a smaller exhaust valve. I might get some new seats in it and go smaller. Especially as I then can just buy good valves.
The speed is hard to measure consistently, but speed without volume isn't great. It obviously needs adequate speed with adequate volume to get the best. Measuring mid port it seems around 42" with the 44.5mm valve and 46" with the 42mm valve. Both over 400fps but the big one is shifting more air 183cfm to 163 both through the carb. According to the 4 vacs.
The conversion graph curves more as it gets higher so 42" to 46" is probably 420 to 445fps. If I divide flow by 60 I get cubic foot per second. If I multiply by fps readings the big one is 1281 and the 42 is 1208 being related to the quantity going in per second. The thing is, doing the same arithmetic, using the stock port flow multiplied by its speed gets 690 units of air to burn in comparison. The air quantity has weight the more weight the more force to oppose the rising piston before the valve shuts abdc.
So I imagine the fastest port flowing the highest cfm for its size, does it best till the speed exceeds a limiting point. Further in these ports near the valve and guide are faster so all I can get is a general idea on the floor half way to the guide.
What's critical seems getting air turned and past the valve the way valves flow best. I doubt BSA understood what they had. You could copy the latest 4v Triumph head for less maximum flow on a big bore engine. I don't know how that compares really, as 4valves are usually good in low lift flow.
Well, just got back from a chilly meeting. (for us soft Queenslanders anyway!) 3 races Saturday, 2 wins and a second. 3 races Sunday 1 win 1 3rd and one did not finish, he broke his lanyard and the motor obviously died. He was struggling as the motor was only the 650 and he was up against the big norton and the triumph again. Also found the battery was flat after his 3rd finish. Had fitted a new rear tyre which was way to big in overall diameter and it upset the bikes geometry by a mile. Still, he is happy with the baby engine as his lap times were only 0.6sec slower than the 740. It will make a very usable spare engine. Gearbox was spot-on too. Would have been nice to have time to have set the carb up properly as it was fluffing at lower rpm, i think the acc pump jets are a bit small. Seems a bit more difficult to get it right with this engine than the larger one. State titles at Morgan Park in early September next up. Found a dyno not too far away and are booking some time, hoo-bloody-rayyyyy finally.
Still going in the winter down there? Must be northern Aus? Good going with the wins. Always a good feeling to get one over on a bigger bike. Says a lot about the rider. I'm gearing up to leave in about 2 weeks for a 10 day, 2 race weekend in Michigan and Illinois late July/ early August. The Triumph is in good shape, waiting on a couple items for the B50 after it's skid across the track last month. If it's not ready, I'll bump the 650 into BEARS and see what happens....
Queensland Mike, although the piddly little circuit we were on is up in the Qld/NSW border ranges. Was -1 deg on Sunday morning until about 8am. After living here for over 20 years i have lost my pommie cold weather hardness................. Best of luck with yours. Nick