Need some help with Engine/Axle configuration

[TaderzNgravy]

Whats up guys, I just picked up a nascar style go cart for my little brother. The original plan was to swap out the 3.5hp briggs for a 13hp honda from my old powerwasher. Once we got the go kart home we realized that the frame is twisted pretty bad... which brings us to the new plan.

Were going to build a square stock frame salvaging what we can from the old frame as far as steering parts etc. and were going to upgrade to a live rear axle and disc brake.

What gears would be the best for the 13hp motor for decent acceleration/ top speed. Id like to stick with a centrifical clutch since we may be swapping in a snowmobile engine in a year or two. I think we're going to use a #40 chain since it seems to be pretty strong. The cart has 12x6 - 6 tires.

 

[jpowers]

best gear ratio that i like for speed and acceleration is a 6:1 at the sprocket, and a 12 inch tire your top speed will prolly be around 40 miles an hour(give or take a fue) mind that for every 33% increase in power you have a 10% increase in speed to.

 

[anderkart]

13hp honda
decent acceleration/ top speed.#40 chain
12x6 - 6 tires.

Hey Tad, this is the best deal I've found on a 1" bore/#40 clutch rated for use on 13hp engines: http://cgi.ebay.com/Racing-Go-Kart-.../140495301866?pt=Go_Karts&hash=item20b62c2cea

Assuming your rear tires are actually 12" tall and your leaving the engines governor all hooked up for 3600rpm: You could use that 14 tooth clutch with a 52 tooth axle sprocket and end up with around a 35mph top speed.

With that engine I think you'd still have pretty good acceleration on flat terrain unless the kart or driver was big and heavy.

If you wanna experiment with some other gearing combinations, here's a link to our speed calculator: http://www.diygokarts.com/speed-calculator.html

 

[anderkart]

Hey your engines output shaft has a 1/4" wide x 1/8" deep keyway and looks like this pic right?

 

[TaderzNgravy]

Yep it does. 35mph doesnt seem too fast, id like to see around 50mph if possible.

The motor is a honda gx390

 

[redsox985]

When you're inches off the ground, I feel that 35 MPH is plenty fast. How about you try that gear ratio anderkart suggested, then, if you want more, remove the governor and allow the motor to reach higher RPMs. The centrifugal clutch requires a gear ratio low enough not to cause it to smoke and burn up. Usually no higher than 5:1. Your small tires aren't helping at all either.

 

[Doc Sprocket]

I agree with the above. Mine will do 45 on a long stretch which is more than enough. Actually, kinda scary on a gravelly, pothole-infested road. If I wasn't about to do a major engine swap, I'd actually gear down some more. In my experience, rubber-roasting torque is a lot more fun than top speed. I suppose it depends on your use, too, but most of us aren't doing Bonneville runs with a radar gun...

 

[anderkart]

How about you try that gear ratio anderkart suggested, then, if you want more, remove the governor and allow the motor to reach higher RPMs.

After removing your Governor your engine would have the ability to spin up to 5000rpm and could reach around a 50 mph top speed with the same gearing I suggested above.

Here's some info about removing your Governor:
(your GX390 would be very similar to that GX200/6.5 clone)
http://www.affordablegokarts.com/govenor-removal.php

And here's more info about hooking your throttle cable back up afterwords: http://www.affordablegokarts.com/throttle-linkage.php

 

[TaderzNgravy]

With the gears ander suggested would it spin the tires? They're slicks.

 

[TaderzNgravy]

After removing your Governor your engine would have the ability to spin up to 5000rpm and could reach around a 50 mph top speed with the same gearing I suggested above.

Here's some info about removing your Governor:
(your GX390 would be very similar to that GX200/6.5 clone) http://www.affordablegokarts.com/govenor-removal.php

And here's more info about hooking throttle cable back up afterwords: http://www.affordablegokarts.com/throttle-linkage.php

Yea i was on agk's website last night, its amazing there are so many performance parts for these engines.

 

[anderkart]

With the gears ander suggested would it spin the tires? They're slicks.

I've got a 10hp Honda on one of my karts with a similar gear ratio. It'll spin the tires while taking off on loose dirt, gravel or grass, but not pavement. I weigh 235 but my kart isnt heavy.

 

[TaderzNgravy]

The go cart will probably be around 200 ish with a 100lb driver