The only gain is made by removing restrictions (the air filter AND tubing) thats max gain until You can get unheated and unrestricted air into the engine. Anything below 200mph just doesn't add more than 2%. (On our engines thats 4hp) claims to the contrary are just that, claims !!! Turbo's and superchargers increase air flow by forcing air into the engine under pressure.Super duper Air filters and all the super tubing in the world won't change Flow dynamics. As much as you would like to believe it does won't change that.