Torque converter help

[ROLY239]

Just purchased a 670cc predator engine and I have no idea what torque converter to use. I have been told to use the 40 series but the 40 series is rated up to 18hp and I don’t want to buy belts 24/7. I also have no idea how to install a jack shaft which makes purchasing a torque converter even harder. I’m using 20 inch tires and a 48tooth sprocket. Someone please help me choose a torque converter, Thanks!

 

[KartFab]

Just purchased a 670cc predator engine and I have no idea what torque converter to use. I have been told to use the 40 series but the 40 series is rated up to 18hp and I don’t want to buy belts 24/7. I also have no idea how to install a jack shaft which makes purchasing a torque converter even harder. I’m using 20 inch tires and a 48tooth sprocket. Someone please help me choose a torque converter, Thanks!

48t in the rear is not a lot. You may end up spinning tires and belts with that setup.

Better to go with a 60t or 54t in the rear

here is what you are looking for

https://www.gopowersports.com/40-series-torque-converter-kit-bolt-on-8hp-18hp/

you can drop down to an 8t 40/41/420p type c sprocket on the jackshaft if you like and you MAY be able to get away with that 48t axle sprocket, but still... thats not a lot of teeth.

If you want to get a bigger torque converter, pretty much the only other one that i can think of for a 4 stroke is the comet 780 and you would have to fab up your own jackshaft assembly IIRC.

 

[anickode]

With 20" rear tires you should be looking at a 60 tooth axle sprocket. You don't need to be geared for 55mph at 3600 rpm. And with 22 hp, you'd probably be cooking belts like crazy, even with the proper torque converter.

Comet 780 is rated for that kind of power. No backplate available.

 

[Randy H]

94c is an option as well. About the same price as a 780. They are readily available in 4 stroke tune. 1" shaft. I think 1 1/8“ too don't remember for sure.

Driven clutches usable with both 780 and 94c include, 770D,780D,790D, and 94D in 1 3/16 belt size. Different combos result in different overall ratios and different high vs. low ratios.

I have a chart that lists the different 780 combos, I'll find it if anyone is interested.

The 94c will take more abuse. I don't know if using the 94c with one of the 700 series driven clutches will. I don't know the ratios available when using the 94c with 700 series driven clutches are either. I would like to know.

 

[ROLY239]

I know this sounds kind of silly but I have no idea how to install a jack shaft. Could anyone share a link with a tutorial or some kind of instructions.

 

[KartFab]

I know this sounds kind of silly but I have no idea how to install a jack shaft. Could anyone share a link with a tutorial or some kind of instructions.

So a jackshaft is just a metal round bar that you put the driven unit of a torque converter on and the small sprocket that is connected to the axle with a chain.

What holds the jackshaft and sprocket/torque converter together is either locking collars or nuts threaded into the jackshaft. What holds the jackshaft and let’s it spin are bearings. Usually 2. The bearings can be pillow block which allows for a no-weld installation, just bolt the pillow block bearings to the frame.

A sturdier option is to weld up a motor mount and tube that will hold snap ring bearings that holds the jackshaft.

Or if all that is too complicated to deal with, just get the kit, which has the jackshaft built into the backplate.