[RedBarchetta]

I suppose that with the small gap there is the possibility of exhaust gas reversion occuring, and arguably at lower rpms. The power loss would be negligible (though I'm no flow scientist). I believe if it were a bigger issue there would have been more talked about it here at CC.

There is actually more power robbing occurring further downstream, mainly the 2" ID factory mufflers and the 4-1 collector (which from a flow standpoint is a mess). Many here (including myself) have performed upgrades on the ID of the mufflers with good results, but few (Buckshot Fabrication comes to mind) have tackled the 4-1 problem. The factory SB header is also restrictive and the factory now offers an improved design for those running the big inch Roush motors. Check with your dealer.

-Dean