Depends on what you mean and what kind of racing you're talking about.
OK, your engine is complete and at a fixed power level.
If you're talking about drag racing then you're talking quicker (e.t.) rather than faster (mph). You need to concentrate on getting your existing power to the ground. That means chassis and suspension work will have much more benefit than taking 20 pounds out of your car.
Someone earlier said 20 lbs. is 2 tenths. Actually, I think it would be closer to 2 hundredths rather than 2 tenths.
Take that $500 and put it into your suspension and get your chassis working effectively and you'll be better off IMO.