40 series torque converter setup

[davidfro]

I have a go kart frame that I want to install a stock predator 420cc engine onto. Planning on 20-22" tires, currently has 21" tires. The frame already has a 45 tooth count sprocket on the axle. The engine has a 40 series torque converter (gopowersports.com) attached to it with a 10 tooth output sprocket. Two questions. First, would this setup work fine as is, or am I going to run into problems with these sprocket sizes? Second, what do you think the ideal drive sprocket tooth count would be for this setup? Am I fine not using a jack shaft in this setup? I believe with the frame and engine the kart will weigh in at around 400 lbs, and it's a two seater intended for two adults. I've been playing with app.kartcalc.net, and it seems to think the gear ratio as is is too high and it will burn the belt. I'd love to hear how you would approach this setup for the best experience. I'm fairly new to this.

 

[JoeWiater]

I would upgrade to a 62 or 72 tooth sprocket on the axle. You will have much better acceleration. I have a light gokart with a 72 tooth sprocket and a 30 series torque converter and it has amazing acceleration. With 2 adults and a frame weighing 400lbs I definitely would not keep the 45 tooth sprocket. The 10 tooth sprocket on the torque converter driving the the sprocket on the axle should be just fine. How are you planning to not use a jackshaft?

 

[davidfro]

I should clarify about the jackshaft. What I meant by that was a jackshaft in addition to the torque converter jackshaft, something to help keep the axle sprocket smaller. Probably not really necessary with 20"+ tires.

 

[madprofessor]

Can't go wrong with a jackshaft separate from the TC's built-in jackshaft, if you're willing to spend money for parts, and enjoy the fun of building it to the kart. Increasing the size of your axle sprocket should be done with a sprocket hub and split sprockets. That way you can change sprocket sizes for only about $15 each time, and can swap them out in 5 minutes flat.
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Increasing your axle sprocket size decreases your sprocket's ground clearance. That's when a jackshaft really helps out. You can change your final ratio any way you like, and never change your axle sprocket.

 

[Denny]

You want a 60 tooth sprocket on the axle. I myself do not care for aluminum sprockets especially for off road. They get eaten up quickly in dirt or mud. And will taco easily under shock loads.
You will want atleast a 6:1 ratio with that tire size.

 

[panchothedog]

If you use 20" tires and a 60 tooth sprocket you will be O.K. Any bigger and the gearing will be too tall. The 48 you have on there now is too small, and for the
40 series I think the 10 tooth is as small as there is. I am going to disagree with
MAD . I would much rather change to a bigger sprocket than install a second
Jack shaft and run two chains. Too many moving parts. I run 5 karts in the Southern California desert. Every one of them is a two seater, roll cage equipped mini buggy type kart. They all have 60 tooth sprockets on live axles
and 3 have 18" tires, one has 19's and the other has 20" . I can't remember a single situation ground clearance was a problem.

 

[Denny]

Adding more chains and sprocket adds more complexity and more drag and uses more power and more fuel. It’s Mores law run amok I tell ya.

 

[Joe-405]

You want at least a 60 tooth. I have the exact same setup on my trike. It runs 50mph but it's alot lighter. You will burn through belts I would guess with anything smaller.

 

[madprofessor]

I cede the facts of physics to Pancho and Denny. An extra chain is definitely more complex, gives more stuff to care for and possibly fail, causes extra drag between engine and tires. My main appreciation for dual chains is all about ground clearance of the axle sprocket. A lesser consideration is the chance to use sprockets with more than just 9 or 10 teeth in between. Not much more I can toot about the dual chains, it's just my own style for a given application.