CVT Setup With 100-135cc Two Cycle (Sudam, reedjet etc)


Not sure if it's legal in UAS, but I'm asking more from a general outlaw standpoint.
Has anyone run a CVT setup? If so what did you use?


New member
I haven't seen it done but ask UAS administrator for your area . I can't see why not . UAS is about innovation , but check with the bylaws just in case.


Road Dog

Jack, CVT = continuously variable transmission
I don't think it's any different from a torque converter. Some cars are using them, such as the Toyota Prius.

RadialFin, to the best of my knowledge CVT's ARE legal in UAS racing. I have never seen one run in person.
Thanks, I should've known that because 1 Candy Co. that I worked at and some European machinery that used a, " P I V." or "PVI" transmission that had a crank and a tach. on it, inside were 2 sets of pulleys with radial slots on both sides, then in the middle was a link belt about 20 links wide with side lugs that fit inside the radial slots, belt had fixed length, so as one was squeezed or opened up the out put r.p.m.'s would change. Some how I think that if such a unit small enough to be used on a Kart, it would be not heavy enough to hold up, and there is no way it could be manipulated on the track, we have seen M'cycle engines in the 125c.c. size try to use a std. bike tranny and shift while racing, NFG, won't even keep up with the slowest Sudam 125.
Last edited:


A 4 cycle guy (hotrob) was experimenting with such an arrangement - don't think it worked as well as needed. Not sure what issues he had with it.


I wouldn't be running it in UAS or an oval, but you guys are a smart, experimental bunch so I thought I would askl. Yeah the weight is a concern if this thing ends up being huge. Any ideas what kind of sled/CVT setups I could look at?
It's very different to a torque converter.

thinking it would be cool to build a bad ass rotary valve with a narrow powerband and utilize a CVT to make it usable. There was a CVT was designed for rotax max, worth a second a lap apparently. But the cost was over $1400!

Jack what you mentioned is exactly what I am talking about. Basically you set a fixed RPM and the ratio dynamically changes (within a range) to stay at that RPM.


The belt tends to lose a lot of energy due to slippage. You have a very large pulley that you have to rotate so the rotating mass is pretty high on the primary side. An engine that makes 50 hp but only puts 40 to the ground is not going to get it (80% efficiency). Not to mention, a good kart doesn't require that wide of a powerband.
I have a Shockwave off of a Jr Dragster also another one that is in pieces (taken apart for rebuild but never got to it) and MANY extra parts. I would take $900 for it all
Going back a few yrs. to the old Pine Brook Speedway in N.J., where they ran T.Q. Midgets on Fri. nites, they had then a 500c.c. engine limit, one guy had a 4 cyl. Yamaha bike engine that he sleeved 2 cyls. down from the 600c.c.'s to 500c.c.'s, he ran it with a torque clutch and it couldn't pass anyone, but if he started on pole, no one could pass him. IMHO, the AMTQRA was the best and largest group in the country.


$900 is way more than I would spend to be honest. Good points on parasitic power loss. I guess I will try and find something suitable from a snowmobile to try as a proof of concept and go from there. Hard to know if the power loss would be offset by having peak power, on demand at any speed without testing on the track.
I can understand a CVT not being much help on an oval, but again I'm running on a sprint track with a low speed of 28mph and top of 70+

Azracr do you have any ideas on where I could start looking for junior dragster CVTs? I'll search of course, but its always good to have a reccomendation from someone. I'm thinking of using this with the 100cc rotary I have. Open up the valve, squeeze the head and pump some meth through there. Let'r buck at 13,500 or wherever peak HP ends up.


OK so found out more about the shockwave stuff, and well, their factory is like 40mins away from me....
Things just got interesting.
I think it is odd that people say they loose power through the belt. I have a Polaris Scrambler 400 4x4 2 stroke for a quad with this setup on it and will light up all 4 tires with my fat butt riding it.
I had a Polaris 200 it had torque converter set up bad fast. It would out run a Yamaha blaster with no problems. Plus you can change spring setup in the primary and secondary clutches. You can even set the clutch to come in at the desires rpm.


I looked in to this awhile back. It would be fast as hell, but tuning it wont be for the new guy. Experience would be a must. Haddock ltd builds them for Jr dragsters. They also have a great website to check them out. I will have to recheck out their site to see if more info is available. Could be a fun build, I wasnt sure if the Jr drag versions would be durable enough. I also think snowmobile clutches would be too big and heavy, I dont know if you could get the weights and springs for the smaller engines? My sled is a 900 that makes 150hp compared to my kart having 216cc and about 60-70hp.