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      03-21-2009, 08:39 AM   #34
My master volume goes to 11
dogears's Avatar

Drives: 2009 Space Gray M3 Sedan M-DCT
Join Date: Dec 2008
Location: Cherry Hill, NJ

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Actually the primary cats are one of the biggest exhaust restrictions. By switching to a higher flow spiral core cat, such as emitec, there is a 8-10 peak hp improvement with more than that gained in the midrange. The trick is finding one that doesn't code.

Originally Posted by J08M3 View Post
Yep, that should make it a bit louder. Probably not much though.

The reason I'm looking to leave my resonators and only delete cats it I want a more aggressive sound that's slightly louder under hard acceleration, but I don't want it to sound to raspy or to drone while cruising around. If you look at the $1,900+ x-pipe AA came out with it's no different than your stock x-pipe with resonators minus the secondary cat. I'm looking to accomplish the same thing for a very small fraction of the price. Plus according to a number of tuners there is almost no gain by switching OEM primary cat to aftermarket High Flow Cat (costing $1.300) By retaining stock primary cat I won't need to re-flash my ECU (another $1,000) Also, I've yet to get any answers regarding what the HFC's are made out of (ceramic or metallic), I've never gotten a CFM comparison between OEM cat or HFC (only way to prove it flows more). I don't want some cheaply made HFC (probably from china) giving me issues in a couple of years. Exhaust shop eliminating secondary cats should only cost a couple hundred dollars at most.