Iowa Chapter Director
Join Date: Jul 2002
Location: Ames, Iowa
I have ASP and I have just the underdrive crank pulley. I guess I noticed a small gain, but anything under 10hp is hard to feel anyway. Theoretically yes, it will improve gas mileage. It takes stress off the motor by removing some of the parasitic drag from spinning the accessories. I never really documented mine, or payed attention so I couldn't tell you from experience.
1988 Notch Mustang: - 438W, direct port n2o, t56
2003 SVT Focus: - SCT X3 tuner