1". I have K&Ns and that is how it is with mine. No problem. David Lylis 69 TR6 CC26160L 60 TR3A TS74461LO **************You Rock! One month of free movies delivered by mail from blockbuster.com (http://pr.atwola.com/promoclk/100000075x1212639737x1200784900/aol?redir=https://www.blockbuster.com/signup/y/reg/p.26978/r.email_footer)