well i had the back end off the 08 yz450f this morning, and i thought id shine a torch inside the header and see if its lean/rich. to my amazement the powerbomb on the stock header has a pipe inside welded in so its literally a straight through pipe!!!!! this to me is a complete con. you think your getting a nice good header so you go out and buy just a slip on silencer - and in reality your not getting exactly what you thought you were!!! how dissapointing. so i now have a white bros slip on for sale - as my full akrapovic system is on it's way! mark.