In so many forums, I have read that if you replace the rear muffler on a Z4 M series with a strait pipe, then it has been stated that the low end of the power band is greatly reduced. I am probably wrong, but with the header cats, resonators and the 2nd set of cats, there would be a great deal of back pressure. If there is still back pressure needed, then what size rear pipe could be used ilo the muffler to create the necessary amount of back pressure to have good low end?
