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      01-26-2013, 04:54 PM   #18
Major General

Drives: 08 E90 M3, 99 E36 M3 Turbo
Join Date: Feb 2011
Location: Concord, NH

iTrader: (3)

Do you have a dyno showing that test pipes on a stock x-pipe yield the same gains as a catless x-pipe? I was under the impression the primary cats were the greater restriction, but that the rear cats still posed some restriction.

A catless x-pipe is initially stinky, but after some driving, the ECU adapts and the smell is not really very noticeable anymore. It is still illegal, but so are test pipes though you may feel better about them since they preserve the secondary cats.