Turning the supercharger at a faster rpm produces more boost and more real horsepower! Pulleys are made from AISI/ASE 1144 Stressproof round bar (medium carbon steel) for great machinability and durability. Measurable boost is dependant on many factors, including but not limited to; modifications such as air intake, exhaust, cam, temperature, barometric pressure and altitude etc. We suggest at the minimum to install a custom air intake and a boost gage when running any overdrive supercharger pulley. The ?2.4" pulley will produce 9 to 11 PSI. RPM levels--?2.4" = 13750 sc rpm @ 5500 engine rpm.