Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board The what if A65 67hp challenge.

A rough measure on volumes, the stock Lightning port 65cc, with a flow tested with a bell on the port of 112cfm, the head for the sidecar racer filled to the same length from the valve 73cc, (about +45% flow, from an increased volume of 12.3%) my T/bolt head which was seeping water between head and manifold about 79cc (about + 52% flow + 21.5% volume) (If I use flow readings through the carbs for this one, it's an increase of around 60%, stock being 100cfm OKO 34s being 160cfm, this represents an increase in gas speed of 31.68%). 38mm round port with 44.5mm valve 95cc (about +41% flow + 46% volume) Nothing precise about these measurements. 38mm oval port with 44.5mm valve about 95cc (+79% flow) + 46% volume

Dividing flow by volume gives a figure to represent relative speed. The worst being the big round port at 1.66, next worst stock with 1.72 then the big oval port 2.1, my T/Bolt at 2.15 and the sidecar head at 2.19. The last three are pretty close and much more efficient.

The + 46% volume will work on a 654cc engine, or a 750, however with enlarged headers usable power below 5,000rpm can be compromised by reversion, obviously to a lesser extent on a 750, stock headers lessen this greatly but also limit to a degree top end. + 46% volume on an 883cc engine is uncompromised by reversion with enlarged headers, but the poor flowing round port limits power which falls off around 6500rpm. The same 46% bigger oval port with 79% more flow extends available power to 8,000rpm + adding hp.

The volume percentage increases on the smaller oval port T/bolt heads should cause no problem on smaller engines.

Mark,
You have achieved some fantastic flow numbers with your improvements to the A65 heads.

Am I the only one here who would like to see you bolt one of your motors into a stock frame and head to Lake Gairdner in March? You'd have to run in the 750 class unless you de-bore or de-stroke the 654. Surely one of your cronies would give you a hand. I'm quite sure that PrTom would lend you a hand as I would if we could get there. You could take one of your beautiful road bikes, but there is salt.......

Tom

Working on almost zero $ allows me to carve heads that I have, and test them on the vacs, but I haven't got the money to do a race bike though I have sons who'd like me to, but they are paying for houses and raising kids. I ride my bike all the time so don't want to use it. If Tom wanted to try a head then we'd get a measure on how it worked on dyno and track, but even then posting one to the US from here isn't cheap.

My next project is a Lightning head hopefully welded in the pushrod tunnel where it has free area to be wider. I'll try 34mm to start, squashed oval entering the head aimed where I want the port to go, to try to get just one curve that tightens onto the valve as smoothly as possible and see what is possible through that little 42mm valve. An 'optimal' port should have a taper at the entry so I might add some bigger pipe to the 34mm manifold and use a 36 or 38mm carb. Theoretically it should be possible to get 100hp or more from a hot rod 750 that flows 175/180cfm. The smaller the port the more flexible the power delivery. It would also probably need 11.5 or 12-1 compression and very good complementing tuned exhaust. I know I can get the flow with bigger valves, which may be necessary, but maybe it can be done without the high speed section of port needing to go over 34mm if the shape is good enough.



I need the manifold a little low so the whole port can curve over and down, even if it's straight and turns is fine but if it's high to start and has to go down then up that heavy air has to change direction and it doesn't like it, one turn is enough.



If I use countersunk screws in the manifolds it aligns them correctly every time.

Tony, my older brother converted several t140's to 76 deg norton cranks. It's much easier than doing the beezer a65.
The main cost is camshafts and getting a decent set of norton rods or aftermarket ones.
The flywheel is a turning job.

MAP do rods for Norton cranks in Triumphs. But you can cut the std Triumph crank and bolt it up on a new flywheel.

Nick, MAP Cycle in in the USA does sell forged billet 76 degree cranks, Triumph stroke, for about $2200 and use the Triumph rods.Finding a good Norton crank, rods, and having the machine work done would cost north of 1000 bucks around here..I sold the Sportster so I do have the money.....But I am on the look out for an old 544 Volvo project....

Almost have the previous 32mm Lightning head done, the guides are K/lined and seats finished. Low lift flow looks great but something is making it flatline above .300" lift and it's not up with the 34mm T/bolt head. It makes heaps more noise above .300" but simply flows the same. The ports are small and the floor of the port raised more than the T/bolt, testing with more or less test pressure shows the same characteristic. I'm guessing the port floor is too high and restricting it or the air is breaking off it. I'll try adjusting that first, if it persists after that I can open it to 34mm and see if that's the cause. I can use AMAL carb mounts or manifolds that oval at the head. They would probably work about the same but the AMAL manifolds mount the carb closer which has it's advantages.

Even how it is should make around 70hp. A 30mm AMAL on the 32 port flows enough for about 65hp, but the carb is undersize for even the stock valve size according to what is considered optimum. So 34mm is just 1mm under optimum and should suit the 650 displacement.



Ideally I want to use the wide band sensor and air/fuel gauge we have and get these carbs jetted optimally so we know what jets are suitable with this head on an otherwise stock 650.

Mark, is there any way to measure combustion chamber turbulence/tumble using port flow equipment ?

In David Vizard's book there are references to swirl and port shapes and measures used to create it. Swirl has more benefit in his testing at lower rpm, at high rpm he says the charge is substantially agitated, though he says a small amount of swirl is beneficial even at 10,000rpm. The ports I'm doing are not exactly the same either side the guide and not exactly straight so they probably generate some swirl but I don't know how to measure it. Maybe if the cyl under the head was clear and had string or cotton hanging in it you could see the agitation. High swirl needs less ignition timing. Where he tested was 2,500 and 5degees less timing at that point gave best results.

The bias on a port can also increase flow, a key to obtaining high lift flow exceeding that of many 4 valve heads apparently. If the flow curve of this Lightning head goes up at the same angle after .300" as before it would be pretty good. Same with the T/bolt head really, even though it's better, both reach limits where they flow no more no matter how much more lift they have.

Edit; I decreased the height of the raised floor of the worst flowing port on the Lightning head and flow went up by quite a bit, so I did it a little more and lost almost half of the gain showing just how sensitive it is.

Edit edit; I cut the seats and finished one side around the seats on the T/bolt head now that its guides are permanently in and K/lined. This head works great straight away,160 through the carb and 170 with a bell on the port.

The Lightning head is yet to get within 13cfm of it as much as I stuff around with it. I opened it from 32mm to 34mm, oval shape at the head, and gained zero. The best flowing port on the head is the R/h still at 32mm.

Measuring time. Where is the restriction if its not at the entry and it's not air breaking off an edge some where? The main port is now bigger but flow is the same. The L/h port is 34.25mm wide at the guide the R/h 35.5mm, this seems like the culprit, but it's difficult to get at with the guide now fitted. T/bolt head is 38.5mm wide so to get the same flow the Lightning clearly needs to go wider. There's still some metal in the port as I'd originally done this head with a very small port and didn't want the complication of breaking through, but this seems the key area, if the floor is lifted and it needs to be, it's choked at this point and a little metal removed here makes a bigger difference than the actual port size, and may be the key to 180 through a 42mm valve which would be nice to get if its possible with the next head welded in the pushrod tunnel. So will be looking for 43mm+ width on that head.

David Vizard cut a Chevy head to test the flow through sections of port, the greatest restriction in that was past the seat, the next greatest was the turn past the guide. Seeing both these heads have the same valve and similar seats I expect flow past the guide area is the problem.

Finally got the Lightning head pretty much with the Thunderbolt. 168.7 and 169.5 at .350" lift, and the ports are about the same size as the Thunderbolts but a different shape, it would be interesting to see what shortening the Lightnings guides by 3 or 4mm would do. Good thing about the Lightning head is it hasn't broken through into the pushrod tunnel. And I'm wondering which head might perform best. The ports are bigger than stock right through but still reasonably small.

Looking good Mark. How long is the transition from oval at the head opening to the carb?
What material did you use to raise the port floor? I am thinking of using Cotronics' castable ceramics or RK454 machinable aluminum putty.
One possibility is to 3D print the port, insert it into an enlarged port and fill around it. That way the ports would be consistent.
I have a pair of Ei Blue Max 33.8mm flat slide carbs that I can use for testing.

The manifold is just 34mm id alloy tube squashed a bit at one end in a vice with tabs welded on for countersunk screws, the head is helicoiled so screws can be smaller diameter.

I'll get some casting rubber sometime and take some casts so its easier to see the shape. JBweld on the floor.

Good to see your post.
We were a touch on the worried side that you may have fallen victum to the current fires.

We are good near the coast in a nice little gap between fires down toward the r/h bottom, where its lit up the most, in this composite image. I was actually wondering how close they were to you.

That nice little gap. is another way of saying, surrounded by fire, Stay safe , , I really hope it rains for you

Never got closer than 2 km but Shane was very rightly worried about embers lighting up the paddocks
He has heavy wood a lot closer to him than myself but it was still some nervious nights standing near the fire pump for me.
Lots of burned leaves & small branches covered the fields but nothing still burning ( thank heaven ) .
We are not out of the woods yet as the Erskine Creek fire can still rain embers down but the rain has greened the paddocks enough to lessen the risk.
Musky got burned out both house & shed and I am still to chase up the other members down there as the NBN is still patchy.

Sending you all our best regards Trevor.

Is that KOSO carb a Chinese copy Keihin?

Oko Koso are Taiwanese. All the Keihin tuning parts fit.

Hi DM, working on the idea of finding the best practical port shape. I'm experimenting with an old 38mm round port head, with 44.5mm valve, it used to flow around 160cfm, I altered it and widened the port up toward the valve, without breaking out either side and it tests at 186cfm with no bell on the entry and 190-195 with a 38mm carb but at a bad angle. So I'm filling the big main port section to make a better shape and reduce its size to see how small it can be without diminishing the air flow. Whatever that looks like doesn't matter I'll just make a manifold to suit.

(Edit; So what filling the top of the port did was reduce the port area, and it actually increased flow to 196cfm, so the valve and bowl area and past the guide are flowing good and the main port section was bigger than necessary. I'll try making an oval manifold using 34mm pipe welded to 38mm pipe. I can open the 34mm up a little if necessary and try making the port section a little smaller again until it becomes a restriction. Then I can find a more optimum port size and shape)







A friend made me a test plate so I can calibrate easier and get more precise flow figures, the two flow meters I'm using after a certain thing start restricting air flow which means when they are added the main pressure goes up and needs adjusting back to test pressure, but I cannot see that being right. Basically the air going into the port is being measured but the two meters are running out of flow. Using the plate when it gets here should allow
matching readings from it. It has a few different size holes which can be plugged or not to match the main vacuum reading from the head and see what it adds up to.

I bought some acrylic tube to make a cylinder for the flow bench. I am not sure if I can generate enough smoke to see what is happening to the flow going into the port but it should be interesting.

Potassiom permanganate & glyeserol should male sufficient smoke, just don't buy then together from the drug store.

You will have to re-name this thread Mark, 67HP?????????????????

Thunderbolt port and manifold to suit 34mm carb.



It's much easier to see the port shape taking a mould.




34mm Lightning port on the left compared to Thunderbolt.



The Lightning port is straighter, the T/bolt needs to bend a little to separate the two carbs, The T/bolt is possibly marginally better.
These flow well but may be better if wider where they taper and lose vertical height. The problem is; they are good now and going wider may actually make them worse.

For fun; Wallace racing has many engine calculators, the hp from valve size one is interesting, for a 42mm valve in a well optimized engine, (think very hot) they predict 92hp. Going back to predictions based on head flow they have degrees of tune Street/Strip, Race, SuperStock, ProStock/Comp, Mountain Engines. I don't really know what they represent, and they may move into exotic fuels, but Super stock needs 160-165cfm for 92hp, and a 750 would need to spin to a predicted 8,000+. Race engine predicts around 85hp. Street strip 78hp at the same rpm. A 650 would need around 9,000rpm.

Don't leave one of those on your dressing table when the mother-in-law comes over....................