little or nothing. ther just spark plugs. if you wanted some serious HP gains, then look into turbo, supercharger with the usual additional items like BOV, and intercooler.with the popularity of NOS in recent movies, i recommend not to get NOS. please do not use it on you car.. your more than free and more than welcomed to use it if you want to see engine parts flying out from under the hood or really mess up the combustion chambers. sure, it boost HP like crazy, but at the same time, messes up your engine each time you hit the NOS button and NOS is used..i do not care if its dry NOS or wet NOS, still messes up engine.