I'm guessing here but me thinks you might have some warranty issues with replacement headers, ie if you cooked the valves say. The benefit of the AKRA slip on is that BMW offer it as an approved accessory.
From what Ive read what you fancy doing in practice is very common but the important bit i picked up was you really need to include a power commander in the set up or get the ecu remapped.
Well he will defo have warranty issues if he remaps or fits a PC III. And you will defo not cook any valves by removing a baffle, also if the exhaust system header change cannot be dealt with by the fuel injection system shame on BMW for make such a crap and inflexable unit. The engine will not be flowing an significant amount more air than with standard headers. The problem with this site is that everbody seems to think that the engine is balanced on a knife edge re fuel injection, BMW do not and would not manufacture a motor that could not cope with a very small change to air/ fuel ratio, honestly you could get the same net effect with a change of air temperature of 10-15 C. All this shoite about weak running and dropped valves is just that SHOITE! The valve issues I have seen is down to bad manufacture of a valve, bad lubrication, badly set valve clearances or a malfunction in the fuel injection system. BMW make very good motorcycle engines very occassionally something can go wrong but it would not be down to changing the exhaust system headers. Just my opinion tho'
10 pager now , there's a shedload of information on here if you use search function.
