NOS has been found to be extremely effective, but makes tuning a nightmare, since you want one tune for when the NOS is on, and another for when it's off. These are still in development.

I don't think a turbo is really feasible, but I've often wondered why there are no superchargers. I think basically, the answer is that a 6 hp top of the line engine already puts out too much power for most of our cars to stand, so there's actually no need to add more.

One of our members, Monaroman, did some testing on a DIY NOS system, and posted videos, quite effective.

http://www.youtube.com/watch?v=QaSjoo6uKPU
http://www.youtube.com/watch?v=iIhK_UlJ6nY