NOTE: IF YOU OWN A 19-21 WRX, YOU WILL NEED THE ADAPTER HUB FOR THIS PART TO WORK, LINKED HERE,or OEM part number 12339AA010. Please contact us if you have any questions.

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 it’s job well. The drawback to the factory pulley is that it’s quite heavy. Reasons for this include less expensive manufacturing and using the pulley’s mass to smooth out ‘noise’ in the accessory system (NOT to be confused with functioning as a harmonic dampener, which it does not). The GrimmSpeed Lightweight Crank Pulley reduces the rotational mass of the system, allowing your engine to accelerate and decelerate the rotating assembly more quickly.

Quick Specs

• 75% Reduction in Rotating Mass – weighs 1.1lb vs the 4.4lb OEM pulley
• Machined 6061 T6 Aluminum – high quality, precision construction
• Hard-Anodized Finish – ensures a durable finish and resists corrosion
• Removal Tool Mounting – allows the use of the GrimmSpeed Crank Pulley Tool
• Factory Fitment – direct replacement for easy installation

Design

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 it’s 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 beautiful and works exactly as intended. From the first test drive, you’ll notice smoother operation, faster response and a more enjoyable drive. Much of this is difficult to quantify, but you can see from the datalogs below that when compared to the OEM pulley, the GrimmSpeed Crank Pulley quantitatively improved throttle response.

Another major improvement made is that you’ll find the necessary threaded holes to use our Crank Pulley Removal Tool for safe and easy installation and removal. On newer vehicles, cars can simply be put into a high gear to break the crank pulley bolt loose, but as with older chassis vehicles, this bolt will likely become quite stubborn with time. The use of the GrimmSpeed Removal Tool will make removal quick and easy.

Materials
Like any GrimmSpeed product, these pulleys are built to last. Using locally sourced 6061 T6 aluminum billet, the pulleys are machined and measured to verify critical dimensions before being anodized. The bright dip anodizing process that we use ensures a durable finish that will protect the pulley from corrosion. Lastly, each pulley is laser etched with a sharp GrimmSpeed logo.

Performance
Proven performance from a crank pulley can be difficult to quantify, but when you’re pulley is meticulously engineered, the results are there. Below is a chart showing the free revving of a stock BRZ equipped with a stock pulley and then a GrimmSpeed pulley. It’s easy to see that the engine reaches redline faster and drops to idle faster with the GrimmSpeed Lightweight Crank Pulley installed. That’s improved throttle response that you’ll appreciate immediately.