I just read a great C&D article on the mad scientists of LeMons racing and I have to tell you, I must find more space and time to build a free asylum ticket. Pictured (from the article) is a Honda Z600 with a 1000cc bike engine riding passenger connected to a front jeep axle in the back. (dafuq?) It works(?) and its nutso fast when not on two wheels. What would your choice be for an underdog track car? How would you take down all those GT3 Porsches and new fat M3's?
Mine? well I did spend some time on the swiftnets forum which is both a power finding and economy finding forum at the same time, also where you can buy turbo systems for your 3 cylinder metro and do 150mph in the standing mile...yeah. The article mentioned a SHO powered metro mid-mounted, as well as other bike engined specials of Miatas and lightweight east German cars. I would have to look at a tiny lightweight car and work out the best way possible to stuff power in it like all the other guys here. I thought a metro would probably be just fine, but stuffing a nice lightweight V6 in the back seat would be a good time no matter how you look at it.
EDIT: heres a vid of a geo metro with a bike engine.