OK here we have Dyno run on the same top end with some adjustments still with the FMF Pipe
(RED)with a 39PWK and Closed Air Box No Lid, and a Q Modified Pipe
(GREEN) with 41 PWK, Adjusted power valve spring, No air box, 9" K&N, The
(BLUE) was the same pipe but....we had a 39PWK closed air box with an open lid, plus we found out the Power Valve Spring was over tightened and collapsed <--Note A good idea to keep a spare Power Valve Spring in the Jet Box!