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Even the factory ran 34s, probably on 750s though. But I guess it's a stock class. I might try putting a 32carb on a 34 manifold and see how much it still has. I need an email possibly, I tried to share the Exel file on here but it would not. It depends on power spread but 3 to 4th is great, just buzz 2nd a bit.

Are you allowed to add material to reshape the port?

Ok an update with some testing.
A 34mm port head with 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 vaccs pull 35"w. through it. 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 33.6" 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.

The 32mm Mikuni that has a blended entry 35" 153cfm 305fps and 350 fps. I cannot measure velocity down the port past the needle very easy.

If the figures are right the calculator for hp from a race prepared motor with 32s is 79engine hp at around 8500+. Or 72hp for a street engine if either are possible.

[Linked Image from i.postimg.cc]

Last edited by Mark Parker; 09/22/21 4:48 am.

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A standard box will be heaps better than the crazy set-up you've been using.
In effect you had a lower 2nd than standard and if you were using a close 1st
then you nearly had a 2 speed gearbox! 1-2 massive hole 3-4.
All my comments are related to track use not dirt so how you would fair with
the close 1st and 2nd i don't know but i would suck it and see.
My 2c

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Hi

Mark
So complicated. There are three types of people in the world, those good at maths and those that aren't.

I'll try again: This has the John Hill PES 5speed as well. This looks like a spread sheet I made up.

I had it so that you change primary and secondary gearing, wheel Dia and change speeds and everything else would change for you.

Semper
This site is rubbish as far as trying to add photo's or spread sheet. If you want to send me an email I'll send you the sheet. My email is [email protected]

John

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Yea it's great. I have no idea how these things work but they are very interesting.

I imagine dirt would be wheel spin. I just looked this up. If the clutch was decent and you didn't hit the rev limiter, which in this case may be mechanical.

http://motoaus.com/race/drag-racing/beginners-guide-to-drag-racing-a-motorcycle/

Launching with a high 1st may be possible, some Nortons doing this used wheel spin. Once going the C/r 1st and 2nd could really work for you. I have also seen a guy leaving a half lap after the pack in a 3 lapper and win the race. It was much better to watch than had he left at the same time.


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Originally Posted by JER.Hill
Hi

Mark
So complicated. There are three types of people in the world, those good at maths and those that aren't.

grin

Email on the way.

Mark - I have polished intake port envy!

Last edited by Semper Gumby; 09/22/21 2:41 pm.
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Probably a question about porting is; are you allowed to add material to ports? Some rules are restricted to just removing?

I was studying Vizard's book on porting, a little bit about raising the floor of the port as it gets to the short side turn. What happens is the air wants to go straight, it's heavy and moving fast. So filling that slow or dead area and making it flat makes little difference except it can raise flow a little and raise speed.

On these heads the floor needs lifting to allow the air to turn better and use more valve area. The bowl is the obstacle that turns intake onto the valve.

Speed in the port is hp and torque. Not only a punchier engine but stronger top end because of high speed ramming, especially if you have volume.

So although the thread is about gearing, punch can make quite a difference to getting off the line and what is needed with gears.


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Originally Posted by Mark Parker
Probably a question about porting is; are you allowed to add material to ports? Some rules are restricted to just removing?

(snip)

Most of the rules for this class involve using original materials for components. For example an Alloy barrel would be Verboten. Porting is not restricted.

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Nice seeing Pushrod Tom at Barber.

Okay.

What I did:

Sent the inner gears to Ed V and he back cut them. That solved the box popping out of third. I had no problems shifting or with speed of shifting.

Ed said shim the layshaft to 10 to 12 thousands. I shimmed it to 10 and the box didn't bind.

As previously mentioned I replaced the shift forks as mine were quite worn/bent.

Unfortunately I had a problem with the swing arm that affected handling. I didn't find it until I had to back to the pits after one lap on Sunday when it became a big problem.

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Originally Posted by Semper Gumby
Ed said shim the layshaft to 10 to 12 thousands. I shimmed it to 10 and the box didn't bind.
So, is that the definition of, "Barely perceptible?"


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Originally Posted by DavidP
Originally Posted by Semper Gumby
Ed said shim the layshaft to 10 to 12 thousands. I shimmed it to 10 and the box didn't bind.
So, is that the definition of, "Barely perceptible?"

Being back cut the gears should hold in by themselves (as I understand it) by having the added endfloat this allows enough movement on the lay shaft to prevent overloading the selector forks. On a standard box the selector forks are keeping the gears engaged so you then need as little permissible end float as you can get away with.

Course, I could be talking crap but it sounds plausible. Ive never had an back cut box jump out of gear.


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Semper, did the gears get re-heat treated after the back cut?


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Originally Posted by Allan G
Semper, did the gears get re-heat treated after the back cut?

I don't think he did Allan. The gears came back pretty quickly. Interesting to see how long it lasts.

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Originally Posted by Semper Gumby
Originally Posted by Allan G
Semper, did the gears get re-heat treated after the back cut?

I don't think he did Allan. The gears came back pretty quickly. Interesting to see how long it lasts.


Nick L might be a good one to answer, the CR Box I got from him was spot on, that had backcut gears, I dont know if they were re-heat treated but it works well. To be honest, Im just curious as some of my aquired gears are a little worn and they would benefit from being cleaned up and better still back cut.


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Nick seemed to think that heat treating would require some fettling afterwards to get them to work on the shafts. So perhaps considering the time element I'm lucky.

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What gear combination did you end up using Semper?


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I asked for STD 1st CR 2nd STD 3rd and 4th.

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Anybody know somebody who can cut gears here in the US. Not getting responses from the guy in England.

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[email protected] in the UK. Or did you try them?


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I think I did. I'll try again. I have this vision of the perfect 4 speed BSA gear box. I think I know what it looks like.

Yep that's the address I used. Crickets. Must be busy.

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With a splined shaft smile It could be possibly fettled in the cam track to make neutral selection easier but the 5speed is the business for perfect ratios, nothing like the ratios Quaife chose, for reasons beyond me. And it's already back cut. The ratios Triumph owners dream of.


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If you are after close gears i know someone who has some.

OR, talk to Dave Madigan he can get them cut/hobbed. The shell and male gears will
be very expensive in small batches though. I've already been down that path.

Allan, the 'box i supplied you did not have raked gears, they were just all new and the
box was setup properly.

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Yes Nick. I need another close ratio 2nd. But I need to cut a different set for first. John recommended someone in England. EDv the same guy. Tried the email but no response. Might be a bit distracted for some reason...

Is there someone else that can cut some gears? Dave is also in the quite busy crowd but ill ask.

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Ahh sorry Nick, my mistake. Still a nice sweet box though.


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There is a firm here that i went to years ago for making me some 2nd gear pairs.
The bloke's actual comment was ' if they wanted to make gears bloody awkward
to manufacture, these are them.' He quoted me about $350 per gear, that was
back in about 2000. In 10 off lots.
The 1st gear pair are quite straightforward though, they shouldn't be too bad.
i suspect you are looking for something between close and standard ratio wise.


Anyway Bill at KRS racing here has the 2nd's he ended up with that last load of
a65 gear that came out of the 'states, from baxters was it? I don't know how much
but i know they are not cheap.

Maybe you should have bought that close box i offered you ages ago eh?
It's working well in Matt's 650 spare engine on his outfit.

As i've said they are ok until you start putting a lot more torque through them
then they just dissolve dogs and break layshaft top gears,etc..

Nick

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I'd use what you have and just give it some hp. The factory had a 654 race engine with 66hp, in 1970, equivalent to 58hp at the wheel. A stock CB750 maxed at 54rwhp at 8000. My long post on the competition board has a chart comparing hp. My copy of Hailwood to Vincent came today it's so interesting. Lots of stuff on outfits. They said they bent mainshafts and wrecked selectors and jumped out of gear. But outfits are hard on gears. It's hard to be an A65 owner and not laugh at many of the stories on them being raced. The obvious is that vibration needed addressing.


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