Your factory crank pulley is responsible for transferring energy from your crankshaft to your water pump, a/c compressor and alternator. It does this by way of a rubber belt and it does its job well. The drawback to the factory pulley is that it's quite heavy. The GrimmSpeed Lightweight Crank Pulley reduces the rotational mass of the system, allowing your engine to accelerate and decelerate the rotating assembly more quickly.
The design process for this pulley ensured that a perfect factory replacement fitment was maintained while performance was maximized. It's a common misconception that the mass of a crank pulley alone determines its effectiveness. The truth is that it's actually the moment of inertia that affects the pulley's ability to improve engine and throttle response. The moment of inertia, in non-engineering terms, is a function of not only the mass of an object, but how that mass is distributed about its rotational axis. A lower moment of inertia means that less torque is required to spin the crank pulley and, in turn, the crankshaft/engine. Our engineers took great care to keep the already minimal mass as close to the center of the pulley as possible without sacrificing its strength.
The result is a pulley that fits well, looks beautifully and works exactly as intended. From the first test drive, you'll notice smoother operation, faster response and a more enjoyable drive.
If you've got a 2008-2014 WRX or 2008+ STI, there's an available stretch belt adapter kit that makes this pulley fully compatible with the stretch-type AC belt. (Other aftermarket pulleys don't offer this!)
Available in black, red, or blue finish. Sold individually.
Fits all EJ-motor Subarus, including 2002-2014 Subaru WRX, 2004-2021 WRX STI, 2005-2011 Legacy, 2003-2013 Forester, and more.