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Old 06-14-2012, 09:13 AM   #259
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Join Date: Jan 2010
Location: Worcester, Ma
Posts: 389
My Ride: 2004 330Ci ZHP
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Originally Posted by diablorojo View Post
Getting a custom exhaust fabricated today. Didn't plan on it, but when I removed the rear section of the muffler and measured the diameter of the dual pipes I learned that it was only 2 inches. I was surprised because it was a full Borla exhaust that I purchased years back. That may even explain some of the choking I was experiencing down low.

So now for the new exhaust. Research is indicating that the max HP on 3 in single is roughly 400 HP. Dual 2.5 is roughly 500 HP. The problem, it has to single into a three inch to feed the turbo. If I dual 2.5 from the header to a 3 in single, say midway, aren't I still limiting the system as if it were a single 3 in exhaust?

If the answer is yes, then I might as well do a single 3 in all the way back.

As of now I'm thinking the best set up would be dual 2.25, yes 2.25, with dual resonators (thinking the resonators will slow the flow as much as a dual 2.5 inch setup will) into the 3 inch. Quiet is king for me. I know this will choke off on high HP for regular turbos but not sure how a rear mount would respond. Also, I'm trying to maintain balance because the less exhaust flow the more lag the turbo would see.

I'll be dropping the current exhaust off this evening so I have a little time to try and figure this out...
I never had a problem making 600+whp on 3" turboback exhausts.
If you go with resonators use the perforated cores versions and not louvered cored as those slow down exhaust velocity.
WARNING: This modification is known to the State of California to cause cancer and birth defects or other reproductive harm due to the extreme G forces once turbo kicks in. ~ Nivo
The rest of my signature is reserved for pointless modification bits like: Halos | window Tint | carbon fiber roundels | short shifter
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