Need to adjust the boost on your Whipple equipped 05-06 GT Supercar? Then look no further as Whipple manufactures these high quality pulleys in several different sizes, ranging from 2.75" all the way up to 4.00" 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.