PLEASE NOTE: IT IS STRONGLY RECOMMENDED THAT CARS WITH CATLESS (STRAIGHT-THROUGH) DOWNPIPES USE THE RESONATOR OPTION FOR THE EQUAL LENGTH MIDPIPE.
The Active Autowerke Equal Length Mid Pipe was specifically designed to create equal length exhaust pipes adjusting for the difference between the front and rear banks of the F80 M3 and F82 M4 downpipes before mixing in an X-pipe and creating an exhaust note different from the normal "S55 sound". Engineered for an exact fit on both the F80 M3 and F82 M4, the difference in sound with this mid pipe will be noticeable the first time with an open throttle!
Inline 6 engines naturally have an evenly spaced exhaust pulses which results in a smooth and full sounding exhaust note. The S55 is a bit of an exception though. While the twin turbo system is great at producing power, the unequal length of the downpipes creates an exhaust note that sounds like 2 turbo 3 cylinders. The massive difference in length of the 2 downpipes create exhaust flow and therefore sound issues in pretty much any system configuration. After much research and testing (from many BMW experts) it was determined that equalizing the length of the exhaust pipes before mixing was a solution to this sound problem.
Active Autowerke decided to leverage their expertise in having already developed a single mid-pipe system for the F-series M cars and devoted their R&D resources into developing this mid-pipe solution. While resolving the issues would have been easier in the rear section of the exhaust, Active Autowerke understood most owners don't want to switch out their expensive rear section. Using a patented solution of a crossover with sinusoidal pipes allowed Active Autowerke to correct the downpipe length variance before mixing the sounds giving the expected 6 cylinder sports car exhaust notes.
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