GrimmSpeed Lightweight Crank Pulley Red 2015-2021 WRX / 2013-2021 BRZ / 2013-2016 FRS / 2017-2021 GT86 / 2014-2018 Forester XT

Your factory crank pulley’s job is straightforward: it transfers rotational energy from the crankshaft to the water pump, A/C compressor, and alternator via the accessory belt. While it performs reliably, the OEM pulley is unnecessarily heavy. This extra mass is largely the result of inexpensive manufacturing methods and the need to dampen minor accessory-drive noise—not because it functions as a harmonic damper (it does not).

The GrimmSpeed Lightweight Crank Pulley dramatically reduces rotational mass, allowing the engine to accelerate and decelerate more freely for noticeably sharper throttle response.

Quick Specs

• 75% reduction in rotating mass — just 1.1 lb vs. the 4.4 lb OEM pulley
• CNC-machined 6061-T6 aluminum for precision, strength, and consistency
• Hard anodized finish for long-lasting corrosion resistance
• Integrated removal-tool mounting for use with the GrimmSpeed Crank Pulley Tool
• Direct factory fitment for an easy, bolt-on installation

Design

The goal was simple: create a pulley that installs like OEM, looks refined, and meaningfully improves performance. Achieving this required more than just reducing mass—the moment of inertia is what truly influences how quickly an engine can change speed.

Moment of inertia depends on both the amount of mass and where that mass is positioned relative to the rotational center. By keeping the minimal remaining mass as close to the axis as possible—without sacrificing structural integrity—we created a pulley that spins with significantly less effort. The result is a lighter, stiffer, and more responsive component that enhances drivability immediately.

From the first drive, you’ll feel smoother acceleration, snappier rev-matching, and a more responsive engine. Datalogs confirm the improvement: when compared to the OEM pulley, the GrimmSpeed unit allows the engine to reach redline faster and return to idle more quickly.

To make installation easier, we incorporated threaded holes compatible with the GrimmSpeed Crank Pulley Removal Tool. This is especially helpful for older chassis, where the crank bolt can become extremely stubborn over time

Performance

Quantifying the benefits of a lightweight crank pulley can be tricky, but the numbers—and the feel—don’t lie. In testing, a stock BRZ equipped with the GrimmSpeed pulley reached redline faster and returned to idle quicker than the same car with the OEM pulley installed. This is a genuine, measurable throttle response improvement that you’ll notice the moment you drive your car.

Fitment

• 2013-2021 Subaru BRZ
• 2013-2016 Scion FRS
• 2017-2021 Toyota GT86
• 2014-2018 Subaru Forester XT
• 2015-2018 Subaru WRX
• 2019-2021 Subaru WRX (Requires GrimmSpeed FA20 Lightweight Crank Pulley Hub)