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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > NA Engine (non-turbo) / Drivetrain / Exhaust Modifications > Res Del for x pipe, 2nd cat Del, stk muffler



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      11-14-2012, 01:03 PM   #1
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Res Del for x pipe, 2nd cat Del, stk muffler

well im picking up my 325i this weekend. Getting a few mods done to it asap. The exhaust being one.

But with all the searches ive done i cant really get a solid answer on this ?


I plan to delete the res, put in a x pipe in place of it. delete the 2nd cat as well. If its not too much money id also like to do 2.5 inch piping all the way back from the headers.


Does anyone have a sound clip of res delete & 2nd cat delete?? Or better yet, res delete w/ x pipe + 2nd cat delete?? with the stock muffler?

From what ive read here it shouldnt be too loud, or raspy. the x pipe should help quite a bit with keeping down the rasp.


i looked in the sticky exhaust thread too. I am not going for sound here, just air flow.
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      11-16-2012, 03:00 AM   #2
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Be careful removing all the restrictions and opening up exhaust size (greatly reducing factory built-in backpressure) - on the NA cars it actually has a detrimental effect and you LOSE low end power.

Cars were designed to run in optimum condition with a certain amount of backpressure.

Do a Search on here and do some reading 1st...
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      11-16-2012, 03:12 AM   #3
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Quote:
Originally Posted by 1QuikWS6 View Post
Be careful removing all the restrictions and opening up exhaust size (greatly reducing factory built-in backpressure) - on the NA cars it actually has a detrimental effect and you LOSE low end power.

Cars were designed to run in optimum condition with a certain amount of backpressure.

Do a Search on here and do some reading 1st...
I read about backpressure on the forums last week, I can't remember which one but it's not backpressure that we're losing. The guy made sense that it is the exhaust velocity being too slow. That's why we feel it being slow or laggy. He went on to go about it and I really thought in backpressure too until I read that last week. So now I think it's slow exhaust velocity.

OP I'm running on a 3inch midpipe from headers, no res, no 2nd cat with eisenmann race muffler, and x and h-pipe are for 335. 325, 28, 30i's use Y. BUT someone did say x pipe to reduce rasp. Just never been done yet or shown here.
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      11-16-2012, 09:08 AM   #4
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Quote:
Originally Posted by 1QuikWS6 View Post
Be careful removing all the restrictions and opening up exhaust size (greatly reducing factory built-in backpressure) - on the NA cars it actually has a detrimental effect and you LOSE low end power.

Cars were designed to run in optimum condition with a certain amount of backpressure.

Do a Search on here and do some reading 1st...
ive done 20 searches. no solid answers on this, hence the question.
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      11-16-2012, 09:15 AM   #5
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I know there have been recent posts regarding this - both from a vendor that admitted after dyno tests that the addition of their product would result in slightly lower power in the low rpm's, & members that have dynoed their cars after certain exhaust modifications that also saw a loss...

Don't really want to mention again who these vendors are, but apparently the possibility exists.

And I use the word 'backpressure' loosely - not near enough space to go into gas flow theory (and no one would read it anyway)

Whether or not this loss can actually be felt?
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