Pushing past the limits

[rdenis]

I want to build a cart that has lots of torque (don't care about top end) to do donuts and make the back end power slide in the cul de sac. If I can smoke tires, even better.

Was going to build the frame out of 1" angle, 6.5HP clone.

Need someone to do the math to give me a gear ratio and engine speed to make this happen - proabbaly running 4 inch rims with some cheap slicks.

Oh yeah, driver is pushing 300+ lbs.

Do I need to break the laws of physics for this to happen? Not even sure I could dump the clutch at a high enough RPM to spin the tires in these curcumstances.

 

[modelengineer]

Unfortunately, there is no dumping of the clutch with 6.5hp clones. Only bike engines (which I highly recommend instead of the clone).

To spin slicks on pavement, a 6.5 clone isn't going to cut it. You'll want at least a 250cc motorbike engine, or a sled engine.

 

[1992suburban]

72 tooth sprocket and the lowest # you can afford on the driver (clutch)
add some TQ mods like high compression head, a tq cam. ect ect should be fun.. the slicks will help but will be difficult

be ready for the BIKE ENGINE everyone will push on you

 

[1992suburban]

see.. motor bike engine/sled engine reccomendation while I was posting LOL

 

[modelengineer]

hahaha, well you know its a good idea. Also can be cheaper than modding a clone, and you get gears.

 

[Rotore]

Or a big engine like my 44cubic inch kohler and gear for 6:1-5:1 theres enough torque to burn cheap tires

 

[anderkart]

Without the benefit of a super high torque engine you'd be down to just high ratio gearing and purposely reducing the traction of your rear tires.

Installing the hardest, narrowest and shortest rear tires you can find would be a good start towards your goal. So would designing your kart to cary most of your weight on the front wheels. (you could extend the frame way past the front wheels to get a seating position thats drastically biased forward)

You could also build a 3 wheeled reverse trike design to further reduce rear traction.

Using a torque converter would help a bunch but they cost more than many high quality clutches and can be difficult to locate for sale now. (I've also noticed serveral reports of maintenance issues with converters here on this forum)

Installing a jack shaft geared for a top speed of like meyby 10 or 15 mph would be a fairly low cost option to also consider. Here's a Jack shaft gearing calculator to figure out what gears to select with your rear tire height and engine rpm.:http://www.compgoparts.com/TechnicalResources/JackshaftRatioCalculator.asp (if you'd be leaving the engine stock, enter 3600 rpm)

You can use these calculators to explore your gearing options w/o installing a jackshaft:
http://www.diygokarts.com/speed-calculator.html
http://www.gokartracing.org/Calculate.htm

How large of a rear sprocket you can run will depend on the height of your rear tires. The chain will add an extra 1/2" or so to the overal size. You'll want it all to be at least be a little shorter than your rear tires so the chain isn't touching the ground on flat level surfaces. Heres a chart with the outside measurements of #35 sprockets so you'll know how large you could select: http://www.azusaeng.com/Sprockets/AzSDno35.pdf

If you choose to run 40/41 sized chain and sprockets, you'll find a diamitor chart for those here: http://www.ablproducts.com/40-chain-sprocket.html

 

[ted andkilde]

My son's fun kart with a TAV2 setup, a bone stock governed 6.5hp clone, hard narrow slicks (Cheng Shin 3.5") and a 12/60t rear sprocket drifts nicely on clean dry pavement. It has a fairly long wheelbase and seat positioned forward for a ten y.o. so weight distribution is pretty even compared to a short kart. We're running a 12/45t sprocket right now which is fine for a 100lb rider and a bit too tall a gear for an adult, it bogs a bit for me.

With the 60t sprocket it drifts remarkably well with my 100lb son, endless donuts in its own length, nice opposite lock "chuckability". My weight is pretty close to your target, it will still drift for me but is a little twitchy and when it bites I'm up on two wheels pretty quickly.

For a strictly drift machine I'd recommend a 72t or larger tooth sprocket, short narrow slicks, start with your torque converter secondary set to 3 or perhaps try a yellow spring -- higher settings on the secondary, or a stiffer spring, keeps it at the high torque output range longer. Also yank the governor if possible, hitting the surge point while drifting equals instant traction, which can hurt . If you set your kart up so you can move weight forwards off the driven wheels it'll be much easier to initiate and maintain drifts. You'll need to disconnect the low oil sensor as well or you'll have constant stalling issues.

t

 

[rdenis]

Man I'm an idiot - I forgot to come back to this thread - must be old age setting in....

Anyways, cool ideas from all of you, thanks!

I just got some new toys to play with (Miller 180 Mig, Miller 375 Plasma, King 6" Bandsaw, Chinese 3 in 1 lathe/drill/milling machine combo) - so I will probably cut my own sprockets which means sky's the limit! If I don't go with a M/C engine I'll build a heavy duty torque converter to pull my sorry *** around.

I like the idea of a M/C engine if I can find a 250cc for cheap I'll do that - I can rebuild/make my own parts if need be.

What about upping the HP on the clone? I can get a 13HP clone for around $289 - double the weight and double the HP but not gonna ever rev like a M/C engine. So how much would any of you pay for a 250cc M/C engine in running order?

 

[mike75925]

i pay as little as possible for all my stuff. some junkyards will let whole bikes go for $50. atv engines are also a good idea. most shifter karts run between 80 and 125cc twostroke d/b engines. at least thats what i've seen.