Buy something that you can leave totally standard from an engine point of view, but gut it COMPLETELY. I'm thinking about that Honda they did a few years ago where they took a standard Honda Civic (non VTEC I think) and did a 17/18 odd second 1/4 with it, then progressively cut it up and re-ran it, I think it ended up in the 12's without any engine work??!!! I think it ended up being a floorpan/seat and engine.
