These 50 mm Lower Velocity Stacks with Pivots were developed by Graves Motorsports for your Cross Plane Crank R1. This item is the "Lower" stack assembly ONLY. This stack kit improves power throughout the entire RPM range. The staggered tops allow the cylinders to share the available volume of air in the R1's airbox evenly at low and mid-range RPMs. The shorter than stock lower stacks feed the R1's appetite for big air when the upper stacks raise, thus improving top end power. These stacks developed on the Graves Yamaha Superbike give their riders the drivability needed to win races.