Off-road go cart..need help.

[MotoRacer]

I have a real junked up go cart that i was given a few years ago in my quad shed. I am thinking of fixing it up and having some fun with it back on the trail. What is the best kind of engine to use in it? I want a powerful engine with a lot of torque. Are there any web-sites that I should see that specialize in off-road go-carts and engines for them? What should I do to it to make it a quick go cart to have a lot of fun with? Thanks for your time.

Kye