GFB 13+ Subaru BRZ / 13+ Scion FR-S Lightweight Alternator PulleyIt might be hard to imagine how reducing the mass of a pulley makes a car go faster, but accelerating a heavy factory pulley from say 3000 7000 RPM in a second or two saps a measurable amount of torque. GFB Lightweight Pulleys reduce inertia by up to 85 percent, so most of the torque that used to accelerate the pulley can now be applied to the wheels. This Part Fits: Year Make Model Submodel 2013 2016 Scion FR S Base 2013 2017 Subaru BRZ Limited 2013