HPS. I have tried a lot of cans over the years, HPS and GGB Trail are the only ones that didn't make a lot of noise and run horribly. HPS actually makes a few horse and is snappier than stock. RPMs don't lie. And not obnoxious loud. GGB is cheap and runs like stock but a rusty mess after half a season. Gotta pay for HPS, but worth it. Second year on both of mine. And I don't get any kind of a discount, they are over $450 each by the time they get here after tax and shipping.