If you wanted to keep the normal look, consider getting a small turbo unit fitted to your current car, these can be shoe horned into the engine bay with the battery being relocated to the boot.
You should then look at a gearbox/clutch upgrade to handle the extra power.
I wouldn't want to ram a big engine in.... imaging the turn-in with all that weight up front!
...as with anything though, by the time you have done all that you could have just bought the S. |