update? I just picked up a fiat 500 and debating what route to go.
Well depending on what you want it for then the following are all what i thought of when i was deciding .
1= Renault 5 Gordini turbo engine and transaxle . 200-250bhp
2= Hayabusa engine and Hayabusa sequenetial box . 170bhp or 300+bhp with a turbo .
3= 20v 1.8 turbo vw/audi engine with vw passat/audi transaxle . 200-350bhp
4= 2.3 race vw beetle engine and rancho gearbox . 210-230bhp .
5= subaru turbo engine onto subaru gearbox converted to 2 wheel drive . 250-400bhp
6= cosworth sierra turbo engine onto renault un1 transaxle . 250-500bhp
options 1,2,3,4 and 5 will all fit easyish but 6 is too long and sticks out the back too much . Also the rotary motor is cheaper to get high power from and very small so that\'s why i picked it . Decisions decisions