I'm not into karting or carting (the weight differential rule is rarely in effect), but I came across this video of a 115 HP go-cart.

A little bit of oomph is goin on here.

If that's too tame, there is the Jet Kart that is getting ready for a record attempt.

And finally the link to a set of homebrew PulseJet driven karts. This guy coallesces a bunch of interesting projects including a cruise missle that can be built for $5,000.

And now you know what I mean when I say there is not enough time in this life...