This power pulley will definitely boost your SC up!This combination of power pulley with a slightly smaller belt, will increase your horsepower and torque.This is specially designed for the Thunderbird Supercoupe and eliminates any slippage that may occur. This pulley is neither a 5% or 10%....somewhere inbetween. The special belt goes great with the stock jackshaft pulley and the 5%Jackshaft. You would need belt adjustment for any other changes. MAKE SURE YOU HAVE AN UNRESTRICTED EXHAUST!!!DO NOT USE WITH STOCK EXHAUST. FOR OFF-ROAD USE ONLY. USE AT YOUR OWN RISK....(and have a great time!)