SRT6_Roadster is right... If it is all aluminum you will lose the function of the harmonic balancer, which is important as you could risk a broken crank. All you are doing here is lightening the rotating assembly which could make it seem to rev faster in nuetral. You could actually hurt your performance in a drag race. In drag racing we would try to run lighter flywheels which is the same basic effect you will have here. If we went too light the car bogged and didn't launch like it should. You actually need some momentum of the rotating assembly to get the car moving from a dead stop.