/\/\ Just a word of advice on the adaptor, THAT adaptor wont work because it will disturb air flow to the Karman vortex and buck like crazy under boost from the improper flow. The "mistubishi" adaptor if you look at it carefully transitions the air from a circular flow to square flow, via the change in shape in the bore and the chanels in the corner of the adaptor to flow air to the full grid of the Karman vortex. And so what if its 4"? Thats why the 4-3 couple is included, I do hope they included it. Lately there at Weapon R it seemed they didnt know what parts went in with their own kits. It had to end up being 4" in order to get an adaptor that flows the air CORRECTLY to the Karman Vortex. This was indeed a carefully engineered and designed product for functionality, and thats how had to be