Boyesen 645 Reeds for the Yamaha Banshee and RZ. These are the least expensive, while greatest power producing reed system we have ever tested. Reeds do not generally MAKE power, they are simply a check valve for the intake system. but these actually produce a measurable 1hp through their superior reed action control. Pretty good deal! One set is for one cylinder so you need 2 sets for Banshee or RZ (two cylinders)