I use 5w-30 Mobil 1. I also have the Amsoil filter and a K&N drop in filter. The Amsoil filter seems a little large, but is spongy, and you have to cram the top of the OEM air box over it to get it fastened. The K&N fits nice and neat, but may let more dirt in than the Amsoil (as many people have seen the studies online and in magazines).