Interesting concept, but I agree with 84corvetteC4, don't do it.

 

Maybe get 15-20 hp, but blow the motor in under 100k. hmmm.............
sounds litke the most expensive 20hp I have ever heard of.


And for racing, you would be better suited to fully build the engine, not just swap cylinders. And, if you wanna race on the cheap, forge the 20 hp and remove everything that does not make you go and stop. all the interior save the drivers seat, the side windows (plexy). If you lighten the car by 2-4 hundred pounds You will notice a lot more than 20hp, and your motor will last longer. And, well, taking stuff out of a car you plan on racing is free!