Fairly sure the 4 cylinders use a smaller diameter exhaust, could be wrong though. I don't really know what affects running a more restrictive than stock exhaust could have on the engine but I doubt it could be anything good, with excessive back pressure and such. Might not cause any serious damage but would certainly atleast steal a lot of power. If the piping is the same size then it should be fine I would imagine. I'm no expert by any means though so could be well and truly wrong and will be the first to admit it if someone brings out some facts, but I know there's no way I'd be putting an exhaust smaller than standard on any of my cars