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      06-01-2013, 03:26 AM   #128
First Lieutenant
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Drives: 2008 Alpine White E92 M3
Join Date: Aug 2012
Location: Sacramento, CA

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Originally Posted by epbb View Post
There's a very good chance that if you don't have resonators, and you swap out the primary cats with test pipes, your setup will be very load and raspy.

The primary purpose of test pipes is to replace the primary cats, which restrict air flow through the exhaust. By replacing the primary cats with test pipes, you increase air flow, which increases sound, and also allows the opportunity for increased horsepower provided you take advantage of a software update to match. However, it should be noted that the intent with test pipes, is to keep both the secondary cats and resonators from the stock x-pipe in place, to allow for some sound filtration.

I'm a bit confused with what you mean by Akra cat back. Akra has two different systems. The X-Pipe (Which I suppose could be called cat-back, but isn't usually) and the Slip-On (Axle back). I'm assuming you meant to say you have the Axle back, because I would be very surprised if someone bought the Akra X-Pipe and removed the resonators.

If you really did mean that you have the Akra X-Pipe without resonators, personally, I wouldn't install the test pipes on a resonator-less xpipe. I would double check to see exactly what x-pipe you have, and go from there.

If you do have the Akra slip on (Axle back), then you could try the Test Pipes first, and if you didn't like the sound, get the Akra X-Pipe. It all depends on what setup you actually have.
I have the slip on. The previous owner also deleted the resonator from the stock xpipe...and it already sounds raspy. Looks like I need to consider the Akra pipe... Or maybe pick up a used OEM xpipe and put the test pipes on it.

Just to clarify, can the test pipes be removed and the primary cats reinstalled for smog testing? A pain but it just goes with living in CA.