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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N54 Turbo Engine / Drivetrain / Exhaust Modifications - 335i > why 2.5" how come not 3"



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      12-12-2006, 05:51 PM   #1
denverlicious
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why 2.5" how come not 3"

so im coming from an evo and hoping to get a 335. im just trying to understand why all these exhaust companies are making 2.5" exhausts? From my experience back pressure for turbos arent the greatest thing. Usually a 3" on a turboed car is standard. why is it that the 335er's are using 2.5"

let me know? thanks!
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      12-12-2006, 06:14 PM   #2
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cause were talking about a true dual exhaust from the turbo back, not a single exhaust with a x pipe, or just daul tips. were talking basically 7 square inches of exhaust space in a 3 inch to about 5 inches per 2.5 inch pipe, so 10 inches of space.

Cliffnotes, a dual 2.5" exhaust has about 40% more exhaust flow than a single 3"
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      12-12-2006, 06:45 PM   #3
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yeah but a dual 3" will flow even more!!!!
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      12-12-2006, 06:55 PM   #4
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rule of diminishing returns....larger doesn't always equal any more performance...typically for most turbo cars...a free flowing 2.5 inch piping exhaust seems to do the job of maximizing performance.....plus you have to take into consideration the sound...you want to maximize performance matched with the best sound or tone to the exhaust......
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      12-13-2006, 12:32 AM   #5
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for back pressure, which makes torque.
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      12-13-2006, 03:59 PM   #6
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by your defintion, a 10" exhaust tip will be awesome, like BMW_E90 said, you need some back pressure for torque
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Originally Posted by jgannonloans
yeah but a dual 3" will flow even more!!!!
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      12-13-2006, 09:44 PM   #7
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      12-14-2006, 02:20 AM   #8
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i got a 3" custom piping
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      12-14-2006, 03:28 AM   #9
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Quote:
Originally Posted by cm3rc
i got a 3" custom piping
dude post some vid clips yo !
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      12-14-2006, 12:13 PM   #10
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Quote:
Originally Posted by cm3rc
i got a 3" custom piping

umm? why would you need custom 3" piping arent the 325's NA? for NA cars i know you need smaller piping for backpressure and torque. Your probably losing power. Usually turbo cars need the bigger exhausts due to the volume of air and pressure being forced out from the turbo.
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      12-14-2006, 12:40 PM   #11
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I'm interested in seeing who and how someone will tackle upgrading the downpipes on the 335, I read that a BMW designer said that one of the problem points of a 335 with more power would be that the DP (downpipe) is more prone to overheating and cracking as a result of the greater heat.

From my experience with a turbo car, having a 3" DP is very beneficial, even if it feeds into a 2.5" system. I'd say the DP is a greater priority worrying who's is bigger.

I'd also be interested in seeing an upgraded TIP (turbo inlet pipe) and LIP (lower-intercooler pipe) from the pictures I saw it looks like the stock ones are pretty nice, doesn't seem like there are any "pancake pipes" like there was on the 1.8T. But it's always nice to get the most that you can out of what you have.
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      12-14-2006, 01:02 PM   #12
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turbosquid is right on the money with the downpipe. From my experiences with my evo, the downpipe made the biggest difference in terms of a turbo back.

im not to familiar with the layout of the 335i's engine so i can really say about the LICP and the turbo inlet pipe. But for sure a 3" dp into a 2.5" exhaust doesnt sound to bad.
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