Jackshaft Primary Ratios

my motor makes peak torque at 10.8, which is why I want my engagement to be that high. It is a Vortex RoK TT with a sudam stroker crank, big bore and on dual alky carbs at 143cc. One off custom piece built by Mike Collins and Judges Performance.
I'd love to see that HP curve print out.
 
just remember that when your engine drops below 10800rpm it's going to slip. start's suck at that high of a rpm. Your constantly engaging and disengaging the clutch on the starts and restarts. Been there done that! That's how I know.
 
just remember that when your engine drops below 10800rpm it's going to slip. start's suck at that high of a rpm. Your constantly engaging and disengaging the clutch on the starts and restarts. Been there done that! That's how I know.
Sounds more like a carburetor problem to me. Could be something else, but I'm pretty sure it doesn't tell you where peak torque is.
 
I would engage on the higher end of torque band like 9800-10000. Adjust the carbs as needed and and let her carry you into the sunset. With duel carbs you should surpass the torque and be into the hp quickly. If it’s not enough then I would definitely think about a longer carb space to reduce the high torque band range a bit to make it more user friendly. Also remover what a jackshaft is...It is a toque enhancer. Which means you won’t loose torque and certainly won’t need all the torque that the motor can produce. Basically it will also help spool the engine to where you want it to be.
 
We have a similar set up for our Unlimited - 131, duels on methanol and a Birkey. Our primary is 2.5. I adjust the secondary ratio based on the track size.

We had a learning experience a few weekends ago on a tight D shaped asphalt oval. My thinking was that I would need lots of gear - I.e. a high ratio number for the track. I was so wrong... the motor had way more torque than the tires could deal with at a high ratio number. I pulled the equivalent of 8 teeth off and he went a second faster. Not only did the LF stay on the ground, the drive off the corner was straighter and faster. I mention all of that so you don’t make the same mistake I made with the initial set-up.
 
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Chris correct me if I'm wrong the Birky comes off the primary side and the bully comes off the secondary side right or wrong more or less. Think about it Later Chuck.
 
There’s an old post from years ago that talked about belt and clutch life and how it directly correlates to primary ratios that I can’t seem to find. We all know that coveted 2.71 primary ratio (21 engine, 57 pulley) is pretty much the standard for two cycles with a minimum of a 21 driver on the dry clutch. The post I can no longer find talked about how that primary ratio getting bigger eats up belts and is hard on clutches because you actually lower the engagement significantly to match up to the much higher jackshaft speed you’ve created by downsizing the engine driver, say an 18 or 19 Instead of a 21. Can anyone school me a little on this subject and tell me why I should or shouldn’t put an 18 on my engine so I can keep my 21 driver on my clutch and not have to run a 70 on the rear gear for the very small indoor tracks where I need a 9.5-10.0 final ratio? OR what’s stopping me from leaving said 21/57 and just putting on an 18 or 19T on my clutch instead? Isn’t the whole point of a jackshaft to begin with to keep heat off the crank and rear gears out of the dirt no matter what final ratio you need?

Call Kermit Buller , hear it from him that's his setup

... :) It is NOT Kermit's setup nor was it my idea that originally Kermit learned about it from ME at the last WKA dirt oval race behind Charlette.

The simple of it is in MY theory that a smaller diameter clutch gear puts less stress on the clutch and gear transferring stress to the Axle gear.

The two extents of the theory were first tested by Donald Rati and me. The original idea came from a racer who used it many many years ago with a noram clutch. Our first experience with it(Donald and I) was with a noram Gas and Oil KT100 racing on dirt at Goodhope speedway.
Donald used larger gears(not remembering in total but say around 17,18,19) on the clutch with regular size gears on the axle and I used small gears on my clutch say 13,14,15 with mini gears on the axle.

My setup with smaller gears and mini gears on the axle was better ... :) and we never had a failure.
Hortsman MDC is what we used before Buller ever had a clutch.
I think one main incentive for Buller go get into clutch manufacturing was to put is on a jackshaft as I explained to him I did.

He acknowledged to me my input to him years later at a Hickory Moosefest and it made me feel very good that my idea thrived with him.
I'm honored he felt what I presented to him at Charlette was an ok idea for he has knowledge, ideas and the skill and experience most none of us will every have. .

By the way I think at one time Kermit made jackshafts with two different tube lengths.
I have one of each and used the long tube with our K30 and the short tube with our yammi.

old fun info to remember and write about now ... :)
 
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