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      03-28-2013, 12:35 AM   #39
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Drives: 2013 E93 M3, Jerez Black
Join Date: Jun 2007
Location: Bay Area, CA

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Originally Posted by s4play View Post
Is there any major difference in the ActiveAuto X-pipe vs. the Akra one or Challenge X-pipe from GTM?
They completely change the sound.

I said this over on the Engine / etc forum, but I'll say it again here... the thin Akrapovic X-pipes change the sound. Once they are warmed up most of the tinniness goes away, but I still prefer steel x pipes... and the factory X pipe with it's 200 cell secondary cats actually flows very well, my Turner Test pipes with Akrapovic rear section were within less than 10 hp of my Akrapovic Evolution.

The AA x-pipe and the Challenge sound the same if you get them catless. (the Challenge can also be had without resonators, which I wouldn't recommend as it increases the rasp by a bunch) The AA high flow cats, are in the stock primary location, which isn't as good for scavenging and make it much quieter. The Challenge Race is catless with a resonator, Race + is with no resonators, and the Sport has high flow cats where the Akrapovic has them (past the secondary 02 sensors, so you need a tune or something to deal with the check engine light, which could just be patience and a blind eye) The Challenge street pipe goes after the factory primary cats and does pretty close to zero for power. (I consider anything less than 10hp "close to zero"

Anyway, they all sound different. The Turner test pipes (the ones I recommend because I've used them and they were the first to market, although $400 for a 2' piece of steel with 02 sensor bungs is a little silly) are my current favorite for sound and budget. (they do require cutting the stock x-pipe but it is easier reversible for anyone with a welder)