Gear Ratio?

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D_dog556

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So I am building myself an offroad kart and I was wondering what gear ratio I should use with my kart. The engine I have is 15 hp Honda clone. It is rated at 3600 rpm and has 22.5lbs of torque. I have 18" balloon tires for it as well. I think that the engine is large enough that I could use a relatively low gear ratio. Say maybe 4:1. I would like to confirm this with the experts though.

BTW: The kart and I will way about 450lbs and larger tires are easy to come by.

I am open to any suggestions and I want lots of speed with decent take off.

Thanks,
D_dog556.
 
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D_dog556

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Alright sounds good. Would an 18" tire be ok for this setup or should I go bigger? I intend on taking it through the fields and on the makeshift track we have in our one horse town.
 
Nodroz

Nodroz

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I have 18" tires and they're just perfect for my buggy. Personally, I wouldn't go much bigger. Remember, the bigger you take your tires, the harder it will be for the engine to pull (less torque - more speed). If you're going to take 22" tires, I would increase the ratio to 6 or even 7:1.
 
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D_dog556

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Ok. Thanks very much.

I was wondering about removing the governor from my engine. What would I expect my rpm gain to be?
 
spyder1968

spyder1968

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if you are truly going to be using this kart "offroad" then i would strongly suggest at least a 6 to 1 ratio with 18" tires !! otherwise i think you will find it lacking torque when in sand, mud, climbing hills etc. this will cause premature belt failure.
what torque converter will you be using?
 
spyder1968

spyder1968

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i would highly recommend a comet 40 series or the next one up...which i think is called a 500 series. i have been using a 40 series for a few years with no real problems whatsoever! due to the hp engine you are running i don't think anything smaller would hold up it. my current setup......is an ungoverned 16hp clone w/ header and a tillotson carb...10t on driver and a 70t on the axle....=7 to 1. also i am running 22" rear tires.
while i find that it performs very well, i am a bit of a torque loving freak ! LOL ! i would still like a bit more torque but i do not want to increase the axle sprocket size ( for ground clearance) and i very rarely ever get to use the current top speed so the next change i am going to make is to try the 44magnum driven for the 40 series. it is 8.5" diameter instead of the stock 7.5" diameter. this should give me a noticeable gain in torque without changing any sprockets. i will lose some of the top end, but that is ok with me.
also note.......the 500 series CAN be found a bit cheaper than the 40 series ( this would require a little bit of hunting around and buying parts from different places) but i don't think there is a "magnum" version of the driven if you ever want to upgrade !
there is more information on " frankenstein" ( my kart) on my blog page below if you are interested.
 
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D_dog556

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That sounds great. A forty series sounds good. Now this 44magnum you are talking about. Is it like a 2 minute change or does it take some time. The reason I would like to know this is because if you gain the torque you say it does then I may want to swap them depending on what I am doing.
 
spyder1968

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it would be a 5 minute deal to change it....but....you would most likely need a bigger belt also. unless you already had a fairly long belt AND you had plenty of room to adjust the jackshaft. if you can get away with the same belt by adjusting the jackshaft, you would only need to shorten the chain a bit.
 
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