I look at it this way, each little increase adds up to a lot. Pulleys 3-5 hp, K&N air with silencer removal 3-5 hp, increase timing to 14 degrees 3-5 hp, shorty headers 5-10 hp, synthetic oil in engine, trans and diff 3-5 hp. Pretty soon you have an increase of 17 to 30 more hp. each one...