Quote:
Originally Posted by Sidewinderpb
That's because nobody wants to pay money to throw their car on the dyno twice, just to see the same numbers each time.
Let me just throw up a disclaimer before I break it down for you:
I am not an engineer; nor have I ever aspired to become one. I am also not a BMW guru; just an enthusiast.
That being said - the reason that you see noticeable gains when replacing the downpipe, is that you are removing a restrictive catalytic converter. Doing so, allows the exhaust to flow much more freely - thus the gains.
When replacing the already free-flowing stock catback, with and equally (slightly more) free-flowing aftermarket catback - you are not really removing anything restrictive. Hence, you will see negligible gains.
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Exactly, I can't see there being much resistance over the distance from DP to exhaust tips (with that muffler mod) enough to add up and restrict the turbo and necessitate the upgrade (2.5" pipes for $1K-3K).
I figured I was asking a lot to see data, I certainly don't want to pay for research (multiple dyno runs).