Go Fast Bits Lightweight Crank Pulley Subaru WRX / STI / Legacy GT / Forester XT 2002-2020
Install a GFB light-weight under-drive pulley kit and get better throttle response and more power! How do they do this? 1. Less weight - GFB's pulleys are manufactured on the latest Multi-Axis CNC machines from the highest grade 6061-T6 aluminium billet, making them immensely lighter than their factory steel counterparts. This lower weight yields a large reuction in the rotating inertia of the belt train, allowing the engine to accelerate faster.
The effect is similar to fitting a lightened flywheel and is particularly noticeable in the lower RPM range before the turbo spools up. This is because the power required to accelerate a heavy pulley accounts for a much greater proportion of the available power at low RPM. 2. Under-driving - Additional power increases also come from making the crank pulley smaller, thereby slowing down the accessories and reducing the driven load (particularly at high RPM), without affecting their operation.
2005-2012 Legacy GT
2004-2013 Forester XT