Need to adjust the boost on your Whipple equipped Shelby GT500? Then look no further as Whipple manufactures these high quality pulleys in several different sizes, ranging from 2.75" all the way up to 4.75" in .125" (1/8") increments. A rule of thumb is that each 1/8" of pulley diameter is about 1 psi in boost change. The pulleys are machined from billet aluminum and then black anodized. No special tools required for installation as they are secured with the same 4 allen head bolts used to mount the original pulley.