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Originally Posted by pushrod tom
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.


1955 BSA Bantam D1 Plunger
1956 BSA A10RR Street and LSR Bike
1961 BSA C15S
1966 BSA spitfire
1969 Triumph T100C
1970 Triumph TR6R
1970 Triumph TR6C
1972 BSA Lightning LSR Bike
1974 Triumph T150V
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NickL #848727 05/12/21 6:55 am
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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.

[Linked Image from i.postimg.cc]

[Linked Image from i.postimg.cc]

Last edited by Mark Parker; 05/12/21 6:59 am.

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NickL #848839 05/13/21 11:44 am
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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.


mark
NickL #848888 05/13/21 11:07 pm
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That's a splayed port head, how does a parallel /t'bolt head come up with standard port sizes and valves?
Be interesting to know.

NickL #848900 05/14/21 12:29 am
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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.


mark
NickL #849043 05/16/21 4:25 am
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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.
[Linked Image from i.postimg.cc]

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.
[Linked Image from i.postimg.cc]

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.

Last edited by Mark Parker; 05/16/21 1:28 pm.

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NickL #849116 05/17/21 8:58 am
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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.

[Linked Image from i.postimg.cc]

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.

Last edited by Mark Parker; 05/17/21 9:20 am.

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NickL #849180 05/17/21 11:00 pm
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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.

NickL #849507 05/20/21 11:26 pm
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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.


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NickL #849513 05/21/21 12:26 am
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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.

NickL #849523 05/21/21 2:06 am
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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.


mark
NickL #849685 05/22/21 11:47 pm
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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.

NickL #849928 05/25/21 4:48 am
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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.


mark
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Cheers Mark, will keep you posted.

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.

NickL #850564 06/03/21 10:19 am
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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.

[Linked Image from i.postimg.cc]


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NickL #850626 06/04/21 1:48 am
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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.

[Linked Image from i.postimg.cc]

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?

Last edited by Mark Parker; 06/04/21 11:47 pm.

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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?

Last edited by NickL; 06/04/21 11:20 am.
NickL #850712 06/05/21 12:15 am
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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.


mark
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From memory the rocker ratio is around 1-1.1.
Don't hold me to that though.......
For the t'bolt head, the tubes would need to be crushed quite a lot.

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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,

[Linked Image from i.postimg.cc]

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.

[Linked Image from i.postimg.cc]

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.

Last edited by Mark Parker; 06/05/21 11:33 pm.

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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.

[Linked Image from i.postimg.cc]

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.

[Linked Image from i.postimg.cc]

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.

Last edited by Mark Parker; 06/09/21 8:36 am.

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NickL #851445 06/12/21 11:57 am
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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.

[Linked Image from i.postimg.cc]

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.


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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.

Last edited by Mark Parker; 06/15/21 7:13 am.

mark
NickL #852278 06/24/21 1:15 am
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Well, ran the old thing up on Sunday with the 650 motor fitted and the head i modified
fitted with the weber. Seems good and sounds lovely, all ready for the 'Big-Chill' meeting
in July.

I've told him to take care of my gearbox............lol.

Last edited by NickL; 06/24/21 1:34 am.
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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.

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