Lightweight Crank Pulleys reduce parasitic drag placed on the crankshaft by underdriving the accesories such as Alternator, Power Steering and Air Conditioning. Underdriving slows down the accessories to use less energy from the crankshaft but doesn't slow them down to the point the accessory operation becomes effected. Under 8 seconds: Most of the power gains are produced from the lightened weight of the crank pulley. Tests show that an average of 2.7 HP is gained from every pound of weight that is reduced from the crankshaft. Installation instruction and belt or belt sizes are included in the package.