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When so much is good, can more be better? Or can less be better? There is possibly a happy place. More flow means always more grunt from the vaccs to maintain test pressure. Engines have that, but don't change it without rpm or changes in exhausts, cams or compression or displacement. Though various performance cams are likely similar.

Flow is really measuring how easily air can enter an engine, how it can go through a port, but that is half the story because hp depends on how fast it goes. It's probably worth trying to ascertain speed at various lower test pressures. I've tested a head at half test pressure 14"w and was surprised that the speed was still quite high. It may actually mean something worth while.

A small port in itself doesn't particularly make speed because it can be hard for air to go through a small port at 28"w and it may not flow as fast nor have the obvious quantity of flow of a bigger port at 14"W probably an exaggerated example, but any degree of that would translate to quite a difference in performance. And may be the thing to test for.

This 1st head has bigger inlets to suits a bigger displacement, as flow is probably beyond what a smaller engine can even use. I guess big flow works on a smaller engine if you can get it into the cylinder without having to use impossible rpm. But there will be a point where that rpm increase is unavoidable without a blower. Or it never reaches it at all.

Hp calculators go off CFM, to be more accurate they really need port speed as well. Vizard's porting book show how you can make less hp with a head that flows more. Mainly because it's too big for the engine size.

Is a prediction of 82-85hp from a 750 going to net a higher output than one that predicts 93+ with more flow? And how are those power curves going to compare? Maybe it would be better to test the bigger head at the same pressure setting that obtains flow on the smaller at 28"w and not adjust that vacuum but check flow and speed, if the flow is the same and speed less we can expect a loss at what ever rpm provides that.

[Linked Image from i.postimg.cc]

With the same carb speed there should be effected but near the valve may be more crucial as it's closer to where combustion happens.

[Linked Image from i.postimg.cc]

Last edited by Mark Parker; 09/21/21 3:20 am.

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An update with some testing.

A head with 34mm oval port and 42mm valve.

Calibrating off a plate with 162.4cfm hole. Which reads close to the same each time but is comparative, not necessarily highly accurate with this gear.

Flat out 4 vacs pull 35"w. through the hole. The less vacuum the easier air is going through. It is weird though as the 32mm carb pulled the same 35" but not the same flow through the meters?

The port with radiused entry pulled 33.6"w and measures around 170cfm @ 28" (how ever real that is?)320fps about 1" in the centre of the port and around 450fps toward the valve. I tried this at 14"w for 320-340fps down near the guide and valve. It's still high, as an F1 style head is 380-420fps though some go to around 600fps

Through the 34PWK 34.5" around 160cfm 305fps in the centre about 1" in and 340fps at the needle.

If the figures are right the calculator for hp from a race prepared 650 motor is around 80 engine hp at around 8500+. Or 72hp for a street engine if either are possible. Testing theoretical against actual needs a dyno.

I then compared that to the new 34port 44.5mm valve cylinder head, which is an old one fixed up. The bigger valve means it's closer to the cylinder wall, with an 80mm bore it's less shrouded and additional displacement will help it.

With radiused entry, no carb; 30"w, 188cfm with over 410fps about 1" in the centre of the port, further in it pulled 53"w on the probe, the conversion graph only goes to 400fps or 38"w. So that 53" compares with 46" of the 42mm valve.

I also was curios what the valve did so I took it and the stem out, just blocked the guide. It flowed a little less, 183cfm.

You can see on this photo I lowered the port entry into the head. I had to fill the port anyway, so moved it down.
This old head actually had a 38mm port and the same valve and maximum flow was 158cfm

[Linked Image from i.postimg.cc]

With the 34pwk 30.4" and 175.6cfm, 1" in 340fps at the needle 385fps. At half test pressure with vacuum of 14"w speeds were 300 and 325fps, still very decent. This means it will work at lower rpm and vacuum. Just what that power curve may be like needs testing. This engine has long curved runners that go oval, so a little bit complicated to make.

This is full std lift .385".

[Linked Image from i.postimg.cc]


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If you wonder; why go to a smaller port head that may flow a little less? It's all about exploiting gas speed. Increasing gas speed increases punch. It can also increase top end with the ram effect of speed. Why it's a delicate balance. That makes an engine very willing and nice.

Triumph's late model 8 valve head flows close to the same cfm, but they are not the same, and hopefully this will deliver the strong punch we are after.


[Linked Image from i.postimg.cc]


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Mark, you don't design ant piston the head squish into you engine's?


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I have, but using B44 pistons with domes don't fit. I had tubbed one in when using T140 lower comp pistons years ago giving 11-1 but I improved the ports on an open head with less comp and it was better, not that that was that great but better. It would be an idea if using a flatter piston but the B44 allows an easy 11-1 or more and works well. It's a shallower chamber than a Triumph. A flatter piston and tubbing would be interesting to do. I could mess with that old head and see how it could flow, I was thinking of that, it would be a bit expensive to get pistons though I imagine.

I'm just looking at the best easiest way to improve the basic thing. I was really surprised how the otherwise stock Firebird engine performs. With the 34mm head with 42mm valves. Though vibration is an issue.


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Mark, at the risk of saying what you may think is basic stuff....

A given flow through a port creates a pressure resistance to that flow, as the flow increases the resistance consequently increases as a square.
As you detail, flow as a(ny) number is meaningless for 'a' port, as a huge flow at a low velocity is useless to a carburettor - especially an AMAL which is dependant upon intake velocity to create the pressure depression at the spray tube in order to lift the fuel from the level at the float, that is why for 'a' port, it is possible for a lower CFM at the correct velocity to out perfom a greater CFM at the wrong velocity, because the velocity at the spray tube hugely affects the fuel take up and consequent mixing and also cylinder filling, and is also why GPs need work doing to them to make them work properly.

CFM is also affected by the external static (positive, hopefully) pressure, turbulence and temperature just prior to the carb intake, on an unfaired bike it is perfectly possible for 'a' carb intake to sit within a negative pressure 'balloon' area (even at speed) giving poor results for no obvious explanation.

Last edited by Twin Pot Phil; 09/24/21 9:02 pm.
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I understand pressure difference. And yes still air boxes work even on a bench, it affects it. I can put my hand near the side of the bell-mouth and get more flow on one side. A box must change something and when you add air going past or turbulence or heat it makes a difference. I had an air box on the 883 fed from the front it made no discernable difference, who knows how right it was? You would need to dyno. I have a data logger but it didn't pick the difference. It would need better testing and experimentation.

The old tubbed in head I cleaned up and tried flows around 155cfm, speed is pretty good. But carb would be 38mm and valve 44.5 so down by 33cfm on this head. I think I replaced it with something around 160cfm with less compression for better top end. And that 5cfm was noticeable. The tubbing doesn't seem to hurt it. I don't know that it's worth working on that head though. I took away some of the guide boss and the exhaust valves started sticking. When you backed off down a hill the tappets would get really embarrassingly noisy, hammer away, everyone in the street would turn, mothers rush children to safety, open the throttle and gas pressure pushed them in, and it stopped, which puzzled them. Compression-o-dromic valve actuation I guess. Riding around trying not to back off!!

If the head was tubbed in you could use something close to a flat top piston with less weight and better flame travel, higher compression, so it probably is the ultimate you could do. It would be fun if the port was the best it could be. The 750 Yamaha twin had a tubbed in head it probably went ok for its day. But it was no rocket ship.

[Linked Image from i.postimg.cc]

[Linked Image from i.postimg.cc]

I have no idea what or if I was thinking doing those ports, looks like I finished them with a brick once I had the shape wrong enough. The big valve was a noticeable improvement all the same, and I didn't understand what it was doing. And stuff I was looking at on porting was like holding a pencil in a Norton port and improving flow a bit, and that's my memory from that library book I borrowed years ago.

Last edited by Mark Parker; 09/25/21 4:32 am.

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" I had an air box on the 883 fed from the front it made no discernable difference, who knows how right it was? You would need to dyno. I have a data logger but it didn't pick the difference. It would need better testing and experimentation."

An airbox fed from an opening at the front can have the opening masked (even fully) by airflow (there is factory history on this). The airbox needs to have a certain volume and be connected to the carb inlet correctly (3 x the engine intake volume at max RPM) and the air needs to as unturbulent as possible. Many have tried to log the positive static pressure in the airbox and failed, it needs a very sensitive instrument to detect this. GP sidecars have used airboxes for a while now - despite having loads of frontal area to choose an intake, they have a column that sticks up into the air behind the driver, illustrating how difficult it is to get good air delivery!

Interested in the 'tubbing' as this is what I did to my engine in 1983 along with twin plugs, used the lands for squishing. I wanted to reduce the combustion distance (84mm bore on a hemi chamber) and boost turbulence. The porting was good but left something to be desired, something I planned to sort out later (still planning!!).
I always focussed on port velocity as I was using modified monoblocks (unable to obtain TTs or use GPs at the time), next time I am using Gardners as they are not fussy on port velocity and I can concentrate on cylinder filling.

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It does get very complex.

The tubbing would be interesting to pursue but it would need pistons. Low comp A65 still have some dome from memory though not much. And the work to the advantage ratio might not be that rewarding. I guess until you had noticeably more hp, which would change everything I expect. I wonder what is possible once vibration and durability is addressed. The valve gear will go over 9,000 and possibly to 10,000 but it still needs over rev margin.


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Starting on another good little 42mm inlet, std exhaust valve head, pointless using the stock inlet, they cost the same and flow less.

I need to fix a couple of fins. I bought a few MAP guides. They can be shortened for seals but I doubt much oil goes through there. They machine easy compared to normal bronze.

The couple of 44.5valves I have have a reduced stem toward the head and I don't see the point of the end of the guide never touching the stem even at full lift, so trimmed about 3mm off, reshaped and polished.

Fibreglass side covers may have space for the carbs to move back into the cut outs using the manifolds and spigot mounts. OIFs have heaps of space with no airbox or side covers fitted.

The Spitfire head may be interesting for someone using original GPs. As it's still 30mm but flowing much more. I imagine it would make it very responsive.

This is the 34mm pwk that works so nicely, if the balance can be improved for smoother rpm. A 90 can fix it best, but is a lot of work.

[Linked Image from i.postimg.cc]


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This is interesting, I've done one side of the new head and have odd numbers from it. Did the whole thing then tested. 42mm inlet valve, I'll have to compare it directly with another head.
It's a different shape but not by much?

I think I can see the supple difference, back to back with another one, it's better by 4.5cfm through a carb. In the scheme of things it makes probably no discernable difference on a 650, but may be noticeable on a 744. The calculator predicts over 80 at the wheel Nick, provided I can match it on the other side frown 8,500 seems ok on this engine size with a 90. If that was necessary. And this one should go hard early. Just need a T/bolt casting doing the same.

I think this is how the air hits the valve and is directed and where it's coming from, as silly as that sounds, is dependent on the aim of the port I think and where it takes it. It must make it hit the back of the valve better. I didn't try to do this, it was dark last night and hard to see what I was doing.

Matching it may be a nightmare. I'll hack it out and start measuring. I'm ticking this box at the bottom thinking, I need a robot.

Later... and waiting for JB to set. Pretty radical difference widening it to 39mm, lucky there is metal, a little more metal would be safer but so far so good. Finish and test in the morning, and weld manifolds if the gas doesn't run out. Soda blast and try replacing missing fins.

Last edited by Mark Parker; 10/05/21 9:06 am.

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The left port is pretty much a match and doing manifolds properly means the best flow reading (what ever it actually is) so far through this valve size. The width is a bit daunting to cut, but should kick butt especially on a big bore 750. So this small port small valve head is flowing around 22cfm more than the big valve tubbed in head and at much higher speed. Fitted new inlet guides but the head crushed them and closed them up, so I ordered a 5/16 hone frown

[Linked Image from i.postimg.cc]


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I honed the guides with what I had. Why I prefer K/liners they are very precise.

Even though the guides are full length the flow is just as good. I guess when you widen it for air to go around the valve and guide, taking either away is zero advantage. As with narrower stems I expect.

[Linked Image from i.postimg.cc]

This is as short a manifold I can make for fitting on a BSA frame. This is through the 34mm carb to the 42mm valve that is ready made and easily available. And reading around 168cfm however close that actually is. Everything depends on the calibration hole of the Helgesen plate which is so fast to test. This is excellent for this set up and a 744 I'm sure would be very nice.


[Linked Image from i.postimg.cc]

So this is 8.5" from this end of the 34mm carb to the 44.5mm valve. Through a curved manifold to fit carbs in an RGV frame. And reading around 180cfm.

You can see even though this is a semi-flat slide and works beautifully it's not exactly smooth bore and it knocks back flow on both heads by around 10cfm.
Air filters or gauze does far more to diminish flow. I just want to bolt them on a mule engine and see what they do. And in the real world the little one that is so much less aggravation may be as good or better depending on how midrange would compare.

[Linked Image from i.postimg.cc]

The new one, this looks a bit funny in places but obviously works. That fin needs a piece of alloy gluing on, I've done two up on the top side. They probably stay on ok if you don't straighten them a bit with a little hammer.

It will be interesting how the guide hone works when it gets here. What happens with virtually all the new guides that are perfectly machined is that cooled and fitted into a hot head they crush in, so they are narrow in the middle and that's where they need honing. This Kw hone is a flex hone with balls for this stem size. A K/liner has the guide bored in the head a thin bronze sleeve pressed in and broached and sized very exactly and parallel.


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Interesting discussing this with the guys on the Norish/Westlake site. And it seems the same weird thing. Some of the guys putting the 8v heads on their bikes report more power right from idle, better response as well as top end. One even shared a dyno graph.

I say weird because theory is also quoted, not by someone actually testing, but by conventional wisdom and what's taught. And those with actual experience are correcting him. It's obviously more complex. But basically confirming what I experienced. One guy fitted the Rickman kit to a 650, it made it a bit bigger but he had a clutch that would not now hold the extra power. The exact same thing with a 650 Firebird. Conventional wisdom would say two 34mm carbs will give less low down torque than a single 28mm, but reality seems to have that being far from the truth.

This graph is a Rickman Triumph rear wheel hp. This is up quite a bit on a std 2v per cyl 650 Triumph. It's not revving high but see the lovely flat torque curve. BSA quoted 39.4ftlb from a Lightning in '71, this has 45.65ftlb and it's close to that for a long time.

[Linked Image from i.postimg.cc]

Last edited by Mark Parker; 10/16/21 5:14 am.

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Originally Posted by Mark Parker
I think this is how the air hits the valve and is directed and where it's coming from, as silly as that sounds, is dependent on the aim of the port I think and where it takes it. It must make it hit the back of the valve better.

That's interesting Mark, my tuning mentor (ace sidecar driver Martin Davenport) advised that his porting (non BSA) deepened the port behind the far face of the valve to the guide forcing the charge to turn down more (compared to standard) onto the back face of the valve as it resulted in better cylinder filling (less out the ex port) and better 'grunt' (better turbulence for a burn). I followed this advice and was really pleased with the outcome when I raced (non BSA), all I want now is to flowbech test it to find out how much better.
I'll see if I can clean the heads up suitable for an image (tubbed head) for a comparison.
Cheers

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Looking at that Rickman 683cc power graph comparing to one of Tom's earlier graphs on his hot 650, at 5,500 the Rickman is at 46hp compared to 40hp with Tom's, it's actually up everywhere up to those rpm where either it dies or they back off. Tom's makes power to 8,000 and a considerable amount. And it is smaller displacement. We always look at the bottom line, maximum hp. But the curves are telling a story worth looking at. What if we can get that hp up earlier, as well as pushing hard to 8,000 or more. If you have 40rwhp and you suddenly add 6hp that is 15% and that would be very noticeable, a different animal. We can look at heaps of differences, bore and stroke, cam, pipes compression etc, but what if it's how the air flows?

How it compares to stock might be more to the point, but a number of graphs overlaid would be an interesting exercise. When the BSA factory tested engines they drew the graphs onto the same graph paper. It took them quite a while to get the three to the hp level they had from the 760cc twin. It's on an engine dyno and maybe we can convert it to rear wheel, which would be around 69.2rwhp, a couple more than a 73 F750 Commando and about the same as a 70 F750 3cyl @ 8,300+. A hotted big bore XS750 tested 46hp @ 5,500 like the Rickman, but pulled to almost 64rwhp @ 7,500. All different bores and strokes, cams exhausts etc, but is the difference just how hard the the mixture is pushing the piston because of how much charge goes into the cylinder? And what if it's the nature of how easily the flow enters and how much force the speed is driving it in?


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Interesting, my 650 Triumph land speed race made 55 rwhp at 7000 rpm and 46 ft lbs at 5100 rpm . At 7000 rpm the engine still had 39 ft lbs... Dyno comparisons aren't often equal, this was on a Superflow dyno at 80F , 800 ft elevation..
Later I retimed the cams, shortened the pipes by a few inches and the speed increased to 133 mph, a 4 mph increase that added perhaps 3-5 hp?
The engine has 10.5 pistons with tight squish, moderate Sifton 390 cams. The conservative head work done by Rob Hall....The engine idles at 900 rpm and start one firm kick..
I have the dyno charts here somewhere..


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Originally Posted by Twin Pot Phil
Originally Posted by Mark Parker
I think this is how the air hits the valve and is directed and where it's coming from, as silly as that sounds, is dependent on the aim of the port I think and where it takes it. It must make it hit the back of the valve better.

That's interesting Mark, my tuning mentor (ace sidecar driver Martin Davenport) advised that his porting (non BSA) deepened the port behind the far face of the valve to the guide forcing the charge to turn down more (compared to standard) onto the back face of the valve as it resulted in better cylinder filling (less out the ex port) and better 'grunt' (better turbulence for a burn). I followed this advice and was really pleased with the outcome when I raced (non BSA), all I want now is to flowbech test it to find out how much better.
I'll see if I can clean the heads up suitable for an image (tubbed head) for a comparison.
Cheers
I remember an article on the giant-killing Mead and Tomkinson B50 endurance racers, although I can't find it at the moment, I recall that they described that the most powerful cylinder head they had was a machine shop scrap head from BSA where the form cutter for the bowl had gone too deep. The thinking was that the extra volume behind the valve head brought about an improvement in volumetric efficiency. I can't see how a steady-state flow bench can measure this phenomenon?


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There may be stuff that doesn't get measured or the improvement doesn't gradually appear but suddenly. Because where it needs to go is sort of the opposite of what the factory did and you tend to think how could this be right? You think they are making a venturi to speed it up, but actually it's just strangulation, it may venturi but air to the valve is... blocked! Making it the same but bigger gives more and it's top end, but the bigness is in so many places where it's not helping the blockage.

I was calculating against my 883. It has flow on my readings around 200cfm through a 38mm Lectron but they flow amazing and it uses TMs. So possibly 193-5cfm, with it running lean with guessed timing 85-83rwhp. Transposing that to a 650 it would mean 62.9rwhp with a flow of 143.6cfm. But the 34mm head with 42mm valves is around 160cfm. A 744 would be 71.5rwhp and need 163.4cfm. And the latest 42mm valve head is a little more. But I have a 34mm head with big valve reading 182cfm, what would that do? It would be like the 883 having 216cfm. But how it does it then kicks in. Size to flow is quality or efficiency or punch. And it is speed and ease of flow. Heaps of air moving fast at lower test pressure or vacuum. 216cfm with the same size port is that much more speed and midrange punch, if you can get it. 744 seems like the fun size to mess with. And changing that dynamic slightly could be significant in hp right across the range.

How it works on a 650cc if like the 883 output, then 62.9rwhp = 71hp needing 143.6cfm which predicts 74hp in a calculator, 160cfm, which we have easily, predicts 80+ if you could get it. Just my cfm numbers that may not match other proper benches, but they relate to each other.
744 71.5rwhp=81hp and needs 160cfm which predicts 82hp but the little head can get more cfm, predicting 86hp, the big valve can get 180cfm which predicts 93hp. If it actually works better on the motor and you can get it without sacrificing punch. But the smaller one predicting 86hp may drive better. That's as a race engine, but like the 883 would be very streetable and nice because it should have much better power or punch at low rpm. The 883 is hard to kick, a 744 isn't.

The predictions are for 'race' motors in the calculator. The factory called the Spitfire cam 'full race'. BSA were leaders with cams, the Repco Brabham F1 winning open wheeler, used BSA profiles. What the A65 lacks is a bit of compression, has air filters and not exactly tuned exhaust, but it needs durability and smoothness, both of which can be addressed.

The deepness and curve of the bowl on that B50 is what the charge hits rushing down the inlet. That's what turns it and the better the turn onto the back of the valve the better the flow. It's being pulled in but both are in play. When you lift the floor it's blocking the port and you cannot go very high so you loose the flow you gained, or you can remove floor you just fitted and gain cfm back, or you can go wide, very wide compared to stock. The charge doesn't care it just wants to get through. It will conform to where it's pushed by where is easy. And it's aimed back at the valve. Then the numbers start climbing. Even if it stayed the same flow without the floor it's smaller and faster and very different with it.

What that column of fast air does not handle is to aim down and then go back up, the reason is below it where it wants to go straight ahead there isn't a solid port wall forcing a turn, but space so it goes straight on and interferes with lower moving air. What goes around the walls is directed or forced in the curve, when that comes together it can go down through the valve and the air over the top of the port is driving that. It goes straight and then over in one big curve.

Last edited by Mark Parker; 10/18/21 3:39 am.

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A chart, I just multiplied rwhp x 1.1343 to estimate engine hp. So I could better compare them, though lots of different dynos, so grain of salt. BSA tests are engine hp so not converted. But if you have 36.8hp @ 4,000 rather than 31hp that's what the Rickman 8v does. And the more you have from 3000 the nicer it is.

rpm - Factory 654 - Rickman - Factory A65 760 - Factory 3 - A65 883 - Stock CB 750 - Stock 750 triple



3,500 ------------------ 30.6

4,500 ------------------ 43

5,000 ------------------ 45.3 ---------52 ------------------- 43---- -----------63-----------36.2 -----------------42

5,500 -------54---------52------------66 --------------------49 ---------------77-----------40 -------------------47.6

6,000 -------58-------------------------71---------------------55---------------82-----------45.3 -----------------53.3

6500 -------62 ------------------------76---------------------60---------------86 -----------49.9------------------60.1

7000 -------65-------------------------78---------------------67---------------90------------54---------------------62.9

7500 -------66-------------------------76---------------------70.5-------------93------------59---------------------66.6

8000 ------------------------------------------------------------73.5-------------91------------61.25----------------65.56

8500 ------------------------------------------------------------77-------------------------------60.1

9000 -------------------------------------------------------------69

9500 -------------------------------------------------------------57

The 3cyl was the best peak hp of 3 graphs (1970), it had 30mm carbs and 3 into 1 and they were trying different header lengths. Other lengths were boosting bottom end and loosing top end. The 760 used 34mm carbs. The 654 it doesn't say. They are tuning race engines so not bothering with lower rpm but the triple would have to stay over 7000 to have an advantage on the 654. And the A70 configuration would likely have it. A John Hill 5speed in the 760 would make it almost impossible for the three until they developed it more. And did nothing to the twin.

You might say what happened to the CB750's claimed 67hp? It's basically not getting to the back wheel, where the max was 54rwhp @ 8000. The conversion is based on a F750 Commando where they tested both engine and rear wheel hp. The Honda has a different transmission that could eat more hp.

The factory race 654 would eat the stock Honda. But not like the 760. So rubber mount a bullet proof A70 with 34mm carbs, or an 80x74 90 degree with 34mm carbs. And get it smooth. Add 5speed or C/ratio 1st and 2nd for a super sport. All that management needed to say to the engineers.

Ducati supplied SS900s with additional 40mm carbs and loud mufflers, buyers just swapped them over. BSA could have done the same with mufflers and jets. Just said it was a production race bike, with race parts, and they were not responsible for what owners might do.

[Linked Image from i.postimg.cc]

The more powerful '71 model Rob North three.

Last edited by Mark Parker; 10/18/21 11:53 am.

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Testing at 28"w allows you to see what's happening through a port but in an engine vacuum can reach 100"w on overlap and 50"w with a piston going down. From memory I had a std port at 28" it was easy to pull more vac, more inches, but I cannot remember exactly how many, but the result was very little additional flow. I'd like to compare that. Without plumbing in 4 more more vacs.

So 100"w doesn't pull a lineal quantity of air. And probably the limitation of the port is having a profound effect. I don't have a std head here at the moment. But tested two I'd done. I checked flow at 24" then at 12" where one was 69.5% and the other 70.5% I don't know which is the better way for it to be. The std head was stuck down in low numbers, not getting the flow of either by having more than double the vacuum. One was 124 and one 132 at half vacuum. I doubt the std one got that even with over 30". If a port pulls 135 at high vac and another pulls toward 200 at that millisecond of high vac its a massive gulp and shifting of air to where it will burn with more packing or filling energy in the movement, providing the port size stays similar.

Both the std HD883 Sportster and Norton 750 Commando are no match for the hot A65 654 after 5,500. The Norton peaks at 55.6hp the Harley 883 at 58hp.
By 3,500 Chris's LSR A65 750 dominates all the '70s superbikes tested. With 60.1 @ 5,000 to the Sportster's 54hp, by 6,000 it's 68hp to 55hp. With only the very potent triple getting near its peak power, 1.4hp behind. But it's been way ahead from 4,000. Why we are interested to see a new dyno sheet from that bike.

Last edited by Mark Parker; 10/19/21 7:41 am.

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