Originally Posted by ozinaldo
This is interesting; so when you analyzed the exhaust for the 1M you came up with the conclusion that the downpipes are different and less restrictive than other N54 applications. Can you further comment, to what extend they are less restrictive? Is it still advisable to upgrade to let's say AR 1M down pipes or maybe it is not very cost effective because of minimal gains? I am not only talking about as a requirement for the tune.
The downpipes on the 1M are a different part number than those on the other N54 vehicles. We didn't look at them in depth, but the WGDC was lower when the car was making the same boost as a similarly equipped N54.
With that being said, there are still gains to be had with aftermarket downpipes. I am not saying that the 1M downpipes are ideal, but they do appear to flow better than the 135i/335i downpipes. You will still see good gains with an aftermarket downpipe on the 1M, just maybe a little less than on another N54 vehicle. We mainly offered the Stage 2 for factory downpipes because they do flow slightly better and many 1M owners want a more stealth car with a factory-sounding exhaust.