There is no Cat... We put a Piece of test pipe in to see what Difference it would make with those Brick Style cats mine had. So far its Great, High Flow Cat is up next. As far as Valve Lash Goes, We set them at every 5000 miles to keep on top of it ( its been done 3 times with in 3000 Miles from noise in the Valve train). I dont wanna buy another head for this thing for a long time. Ill check the timing again to make sure. Thanks Jerry Ill try that and see what that does. Im using Octane Booster on Mid grade for fuel mileage reasons, Its done it before this but its getting a little worse this time around.