These are the Boyesen 645 Reeds for the Yamaha Banshee and RZ-350.
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 1 hp 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).