Well it was all the rage many decades ago when engineers discovered large gains in reducing case volume. HP went up, RPM too, they went a bit mad with this single minded theory which led to a 3cylinder 50cc 2T bike putting out some ridiculous amount of HP like 30, reved out to 20k RPM. Only problem was it needed about 15 gears to ride and had a wafer thin power band. Basically nobody could ride it. Can you increase power by reducing case volume....sure. Is it the only way or best way to do it, not necessarily.