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      08-18-2012, 01:56 PM   #17
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Drives: MR E90 M3
Join Date: Jan 2008
Location: SoFla

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I think people are mixing some terminology. IMO the "oem mod" refers to replacing the two large perforated pipes with straight pipes then closing it back up. The "ACM mod" from what i can tell bypasses the center chamber and is essentially a straight through design.

Sounds like the op is asking for a comparison of the ACM mod to straight pipes which according to most should sound identical.
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