Top speed on a torque converter?

[Preduhtor_122]

I have a built stage 2 predator with a .265 hot cam and 26 pounds springs. Going from the back sprocket straight to a centrifugal clutch I had a top speed of about 55-57 mph. The sprocket is a 50 tooth 18 inch tires. I’m gonna be switching over to a 30 series TAV2 torque converter because I’ve currently burned through 3 different clutches. I have heard those affect top speed a lot. I was wondering what I should expect as a top speed switching to a TC.

 

[KartFab]

Hmm so what you really mean to say is the following?

Q: Why are you replacing the clutch?
A: Because I keep burning through clutches.

Q: Why do you keep burning through clutches?
A: Because my gear ratio is either 4.1:1 or 5.0:1

Q: Why is your gear ratio like this?
A: Because it was modified beyond the ideal ratio.

Q: Why was it modified beyond the ideal ratio?
A: Because I want to go fast.

Root cause of clutches burning up:
Too few teeth on rear sprocket.

Solution
1) Change rear sprocket to obtain a top speed of 17-25 mph at 3600 rpm

• Pros: will no longer burn up clutches, will accelerate faster.
• Cons: will have a lower top speed

2) change to 30 series torque converter without changing gear ratio

• Pros: none
• Cons: will burn up belts and possibly damage torque converter. spend additional money for nothing

3) change to 30 series torque converter and gear for a maximum speed of 28 mph at 3600 rpm

• pros: will have the ideal gear ratio, and will accelerate 2x-3x faster than clutch upon take-off
• cons: will not be able to rev past ~5500 rpm

4) change to a "juggernaut" torque converter and gear for approx 28 mph at 3600 rpm.

• pros: will be able to rev the full range of the engine's ability, will accelerate very fast, belts will not burn up
• cons: cost, slightly lower "top speed" than buring up your clutches all the time, possible wheelies.

 

[anickode]

You've gotta fix the gearing, IMO.

A tav2 has a 10% overdrive at top speed, so in theory it will go a little faster, however at that gear ratio, you are probably ultimately limited by drag and HP, so slapping a torque converter on it could likely slow it down due to the inherent efficiency losses of a belt drive. Say your engine makes 10hp, with a torque converter, as little as 7 might actually make it to the wheels, which could limit your top speed if 7hp isn't enough to beat the aerodynamic drag at your theoretical top speed. It will accelerate better, but that's it.

It's exactly why race karts don't use them.

 

[Preduhtor_122]

So what would the recommended gearing be? What should I change the back tire sprocket to? At this point top speed isn’t a priority. I just want good acceleration while keeping a decent top speed without to much wear on the torque converter

 

[karl]

4) change to a "juggernaut" torque converter and gear for approx 28 mph at 3600 rpm.

• pros: will be able to rev the full range of the engine's ability, will accelerate very fast, belts will not burn up
• cons: cost, slightly lower "top speed" than buring up your clutches all the time, possible wheelies.

To be honest, I stopped using my juggernaut , the lack of adjustment and different springs , or any replacement parts sucks.

All you have to do is shim the regular 30 series clutch a little bit,

and it removes the 5500rpm ceiling

Just replace the original bronze spacer bushing, with a thicker steel ring. 0 cost. Wider the spacer, less top ratio, and keeps the belt from getting torn up, just like the juggernaut. The monster moto 212 bikes have a shim like this from the factory.

On a built high compression, 7500rpm motor,
works great, does not limit the top speed like a stock clutch,
and actually accelerates way faster than the juggernaut.
Cause if your clutch is not keeping your motor where it produces peak torque,
you are not getting the full pull.
Tuning the torque converter right can make a huge difference.

So what would the recommended gearing be? What should I change the back tire sprocket to? At this point top speed isn’t a priority. I just want good acceleration while keeping a decent top speed without to much wear on the torque converter

My 212cc monster moto is fine with the 50t in the back, I changed the drive sprocket from 10 down to 9, and 19in tires. regular 30 series, no worries, gets out the hole well and hauls. But 12 to 1 compression helps, you may still need more reduction.

 

[Preduhtor_122]

Would this work

 

[karl]

Would this work

How am I supposed to know?

The spacer needs to have a 1.25in OD, and about 1.09in ID

1/4in thick or less.

 

[anickode]

So what would the recommended gearing be? What should I change the back tire sprocket to? At this point top speed isn’t a priority. I just want good acceleration while keeping a decent top speed without to much wear on the torque converter

With 18" tires, I wouldn't run less than a 6:1 ratio. If the kart (and/or you) are on the heavier side, you might want to lean toward a 7:1.

 

[Preduhtor_122]

So what would the recommended gearing be? What should I change the back tire sprocket to? At this point top speed isn’t a priority. I just want good acceleration while keeping a decent top speed without to much wear on the torque converter

With 18" tires, I wouldn't run less than a 6:1 ratio. If the kart (and/or you) are on the heavier side, you might want to lean toward a 7:1.

I’m running the TC on a Coleman BT200x Mimi bike with 18 inch tires and I’m about 155

How am I supposed to know?

The spacer needs to have a 1.25in OD, and about 1.09in ID

1/4in thick or less.

So as long is it fits where the original spacer is and is 1/4 inch thick it should be fine correct?

 

[anickode]

I’m running the TC on a Coleman BT200x Mimi bike with 18 inch tires and I’m about 155



So as long is it fits where the original spacer is and is 1/4 inch thick it should be fine correct?

I guess I missed the mini bike memo somewhere along the way.

Might still want to look at a 6:1 ratio. That thing would be a rocket.

 

[karl]

So as long is it fits where the original spacer is and is 1/4 inch thick it should be fine correct?

The idea is the wall thickness of the spacer is slightly thicker than the original, so the sliding pulley cannot move over it, and locks the clutch out of high ratio. If it does that, then yes.

Might still want to look at a 6:1 ratio. That thing would be a rocket.

Yeah, that should do well.

 

[Preduhtor_122]

I’m hoping it does perform well. At one point running a centrifugal clutch I got it up to 60 but I really do miss the acceleration. As previously stated I would be fine with topping out at atleast 40-45 while gaining a good acceleration and torque

To be honest, I stopped using my juggernaut , the lack of adjustment and different springs , or any replacement parts sucks.

All you have to do is shim the regular 30 series clutch a little bit,

and it removes the 5500rpm ceiling

Just replace the original bronze spacer bushing, with a thicker steel ring. 0 cost. Wider the spacer, less top ratio, and keeps the belt from getting torn up, just like the juggernaut. The monster moto 212 bikes have a shim like this from the factory.

On a built high compression, 7500rpm motor,
works great, does not limit the top speed like a stock clutch,
and actually accelerates way faster than the juggernaut.
Cause if your clutch is not keeping your motor where it produces peak torque,
you are not getting the full pull.
Tuning the torque converter right can make a huge difference.



My 212cc monster moto is fine with the 50t in the back, I changed the drive sprocket from 10 down to 9, and 19in tires. regular 30 series, no worries, gets out the hole well and hauls. But 12 to 1 compression helps, you may still need more reduction.

I’m sorry I was understanding this wrong so the width isn’t what matters it’s the actual thickness of the bearing so as long as it’s slightly thicker than the original (1/4 inch thick) then that should be fine correct?

 

[karl]

I’m sorry I was understanding this wrong so the width isn’t what matters it’s the actual thickness of the bearing so as long as it’s slightly thicker than the original (1/4 inch thick) then that should be fine correct?

I hope this clears things up, this is how monster moto did it, put another spacer ontop the regular brass spacer.

 

[Preduhtor_122]

Okay so just basically placing a Extra spacer on top of the original bushing essentially making the original bushing “thicker” thank you. I think I got it now. I’ll post an update as soon as I get it on

 

[vpd66]

I believe Monster Moto did this for 2 reasons. First they wouldn't sell a mini bike that would flip over on take off, so they used a 5:1 gear ratio to keep the front end down on take off. Then I'm sure there was or is some regulation on top speed. So I think they put the spacer in the drive clutch to keep it from going into overdrive and keep the top speed under 30 mph.

 

[Preduhtor_122]

Update fellas. Installed today and since I also got a riser plate from OMB install was a breeze. The torque is crazy and my top speed is actually impressive. Around 40-42. I still have yet to dry the shimming trick yet. Once I do I’ll post more updates. The thing really is a rocket but I can feel it wanting to give me more but that overdrive really kills it

 

[anickode]

Update fellas. Installed today and since I also got a riser plate from OMB install was a breeze. The torque is crazy and my top speed is actually impressive. Around 40-42. I still have yet to dry the shimming trick yet. Once I do I’ll post more updates. The thing really is a rocket but I can feel it wanting to give me more but that overdrive really kills it

You can rack the driven spring into the tightest position to help keep it in a lower gear longer as well.

 

[bob58o]

I wish someone could convince me about those bushing spacer things. People say that they can’t rev out with a TC. They blame the Overdrive on the TC.

Is it really the TC overdrive? Or is the final drive ratio combined with lost power through the belt drive??

Meaning would 6 :1 sprocket ratio with 0.9 :1 overdrive from the TC perform differently than 5.4 :1 sprocket ratio combined with a 1 :1 ratio from the TC???

Theoretically I don’t really see a difference? Mechanically there might be some things going on. I see the bushing/spacer only as a means to limit the range of the CVT. Like mentioned above, seems like a way to try to keep the front tire down on a mini bike.

If a minibike designer wanted a 30 series TC and 5.4 :1 final drive ratio on the big end, they would use 6 :1sprocket ratio. That would be 16 :1 drive ratio off the line.

With a spacer to limit TC range to 1 :1 when fully shifted, the sprocket ratio could be 5.4 :1. That would give you the same final ratio on the big end, but give 10% less torque off the line.

I see these spacers all over FB. I never needed one. My TCs spun 7-8k+ RPM without a spacer. Just made sure the final ratio was set up to allow my engines to turn. And that gear ratio set up made it hard to not do wheelies off the line. With a spacer, the wheelies would have been 10% less impressive.

 

[wooden]

Here is the discussion about torque converter with 18" tires and 50tooth sprocket so since it is simillar to what I have, I can write my feelings about such configuration.

I have heavy frame - 80 kg, maybe more
4 wheels 19" with big mud thread
sprocket on axle - 52 t
sprocket on torque converter 10 t
212gx engine still with governor


It is able to make about 35 kmh (about 20mph) on gravel with me (more than 100kg) on the board.
It still has a power to take off in deep sand although You feel some lack of the power ;-)

 

[karl]

I wish someone could convince me about those bushing spacer things. People say that they can’t rev out with a TC. They blame the Overdrive on the TC.

I understand , on paper it does not make sense, but hear me out

My monster moto 80, (212 swapped) light bike 16in tires, 60t rear, 10 front. Steep gearing. Camshaft makes power below 6500rpm.

Without the spacer, it cannot rev past about 5k, cannot reach valve float. Dog once the tc hits overdrive.

With the spacer, and a 11 tooth front sprocket, no other changes, it can reach valve float, 6500rpm easy, and gained 15+mph, and just made the bike way better.

Just my experience, do what works for you.

Many people report a similar problem, and yeah, lots are due to poor gearing, but I dont think it's always the case.