My buddy built a 400 ex go cart and it beat or friends 250r quad it is a cool toy with alot of power and half the lbs. of a quad snowmobile disc brake helps stop this beast.

 

Me and a friend built a CB450 powered go cart in school. That thing would FLY!!! He had an oddessy that we tried putting a 580 twin rotax from a sea-do. Couldn't come up with a cooling system that would support the water tuned pipe.

We also built a minibike that came with a 1.5 HP engine. We dropped a CB360 twin 6-speed in it. had the battery and everything ready to ride. Never got the rear sprocket mounted though.

 

My friend bryan has a 880 cc ski do rotax engine in a gocart. It needless to say, flys...

-nick