Unorthodox Racing Ultra Street lightened underdrive pulleys are CNC-machined from lightweight 6061-T6 aluminum billet. Premium 6061-T6 aluminum billet ensures the consistency of the material's strength and balance. Tolerances are held to within .001", and numerous machining steps are used to ensure the lightest possible design. In addition to fit, finish is just as important and each piece is representative of this. Power Gains Unorthodox Racing pulleys can provide gains of 5 to 12 HP and 4 to 8 ft.-lbs. on normally aspirated engines and 8 to 16 HP and 8 to 18 ft.-lbs. on forced induction engines. These are average gains. Gains as high as 37 HP and 45 ft.-lbs. have been realized on modified forced induction engines. These gains are obtained in two ways. First, and most important, is the weight loss. An average of 2.7 HP is gained from every pound lost off the crank shaft. 85% of our gains are from weight loss. The rest of the gains are from underdriving, which accounts for about 15% of the total gains. Unorthodox Racing does not push underdriving for two main reasons. Our main reason is to keep charging systems, air conditioning, power steering, and water pumps moving fast enough for every day driving. Second, not much horsepower is gained from extreme underdriving. All of our underdriving is done with the crank pulley, not the accessory pulleys. This is done so maximum weight loss can be achieved at the crank where most of the horsepower gains are found. Please note: Belt(s) not included. Instructions provided with underdrive pulley will give recommended belt sizes. Belt(s) can be purchased at your local auto parts store. Applications 2004-2006 Scion xA 2004-2006 Scion xB