My Setup.... advice...

[ericspants]

Hi, So im super new and im looking for some advice.
I have an older carter 1 seater with a Honda GX240 8 Horse.
Torque converter and a 72 tooth drive sproket and an 11 tooth on the converter.... it has 22 inch rear tires and a #40 Chain.
Im looking for more top end speed but dont want to lose any low end torque... is my gear ratio good?
Im looking into getting a GX340 or GX390 honda but will the extra weight be worth the extra power? would i have to upgrade my axle or framing?
And last but not least would smaller tires make me go faster? as long as they have clearance... the 72 tooth sproket is big....

 

[fowler]

the weight doesnt change much and u get 5 more horse power (gx390) the cart shoud be built to be stronger than requied but i am not sure as i dont known what the kart looks like
or just get a bike engine

 

[Doc Sprocket]

An increase in maximum RPM would increase your top speed without altering any characteristics. Maybe look at altering or defeating your governer (assuming it's currently unaltered). Many here will say that valve float will then limit you safely around 5-6000 RPM. I can't comment, never done it.

As speed is a function of wheel RPM, you can address the following- 1) Engine RPM- See above. 2)Gear ratios- You can regear, but as you know top speed and takeoff are a trade, and at the top end of things, the engine has to have enough power more on that later 3) Tire Circumference- See regearing. Smaller tires give you faster accelleration, at the expense of top end. Smaller tires will NOT let you go faster, they'll just likely achieve thier own top speed faster.

The MORE part- I recently managed to get more top end by gearing lower. You read that right. Lower. I changed my final drive ratio from 4:1 to 4.8:1 and picked up a couple miles an hour. How?
I was feeling and hearing my engine lug at top end, didn't seem like I was hitting my governed 3600 RPM. Means the engine's under too much load. Not having a tach meant doing this by the seat of my pants. My GPS confirmed an increase in top speed. Anyhow, I figured if I ligtened the load my engine was seeing, It could spin up to 3600, and if the gear ratio wasn't too deep, I might actually increase top end. A delicate balance for sure. Anyhow, the long and short of it was that it worked. My tires are about 18" diameter, my kart weighs well over 300lbs WITHOUT my weight (145) added to it.

That said, let's look at your numbers. Your final ratio is 6:54:1. I'm assuming you're governed to 3600, with 22" tires. My favorite speed calc says you're good for 36MPH, assuming your engine has the grunt. Since you have a torque convertor /CVT, I think you're safe to gear a little higher to achieve a higher top speed, the CVT should help compensate in the bottom end. Try 5.5:1 or 6:1. Any higher, and I think you'll run outta horsepower. For 6:1 your sprockets need to be 10T and 72T, or 11T and 66T. Change whichever sprocket you want. For 5.5:1, you'll need 10T and 55T, or 11T and 60T (actually 5.45:1) change whichever you prefer. If you go much higher than that, you may not have enough engine, and your torque convertor may start stressing at the bottom end. Cheers!
PS_ Speedcalc says 43MPH for 5.45:1

 

[ericspants]

Wow, very detailed answer thanks! You helped more than you know!

 

[Doc Sprocket]

Glad to be of service!