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BMW 3-Series (E90 E92) Forum > BMW E90/E92/E93 3-series General Forums > Regional Forums > UK > UK Technical Forum > N/A Muffler and/or cat delete question



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      10-19-2019, 10:01 AM   #1
Mikey77T
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N/A Muffler and/or cat delete question

New member here,

Sorry if this question has been answered, I did find a few threads on this but no final answer hence the question!

I have a E93 325i and was wondering whether a Muffler delete decreases performance or has no adverse effect?

The BMW performance muffler is too expensive for my budget, but from the looks of it its a straight pipe muffler with perforations to resonate the sound!

So, my line of thinking is a muffler delete would be cheaper (louder) and same performance etc as a BMW performance muffler if any.
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      10-19-2019, 12:14 PM   #2
aaronblack
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Muffler delete for a N/A should be fine. You may go down on torque at low rpm but overall nothing adverse could happen. Even a expensive 1k performance muffler wouldn't do anything tops maybe 10bhp for a N/A!

If you want the sound delete the muffler and the secondary cats and nox, then remap your 325i to 330i and you'll have it all.
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      10-20-2019, 01:09 PM   #3
Mikey77T
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Thanks for the reply,

So apart from the noise etc, am i correct thinking the performance muffler is a straight through?

Just trying to see why BMW would make our mufflers so restrictive? is it purely for noise pollution or does the restriction also create pressure etc. to help with power/torque?

And if it is for power/torque, why would they make the performance one straight through!

My point being is either the restrictive one is good or the performance muffler! or neither of them actually make that much of a difference on power/torque and are just for less or more noise!
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      10-20-2019, 06:08 PM   #4
therealdb1
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You cannot over simplify the exhaust system on any mass produced car to that extent. All exhausts are a compromise and a balancing act between flow, noise, what is good for the engine and how much it costs to produce. The latter is becoming increasingly important these days as the number of serious recalls due to using "cheap" parts in the initial build demonstrates.

BMW, along with every other major motor manufacturer, build cars to make a profit which they do by selling as many as possible in as many different markets as possible.

By consequence, they have to satisfy many differing legislative requirements whilst appealing to everyone from "boy racer" to "little old lady" no stereotyping or sexism intended.

You might be prepared to put up with racing volume exhaust notes, rock hard suspension that is so low you cannot get over speed ramps, carlos fandango wheels or matt black bonnets but there are many content BMW owners who would not.

BMW produce a car that is competent in all areas and good in others that appeals to the widest audience but if you want to buy one and change parts being prepared to live with the side effects that come with those changes that is up to you.

If you want a bespoke car from the factory you might need to chat with someone like Bentley or Aston Martin but their cars will make a BMW performance exhaust look like loose change in your pocket!
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      10-21-2019, 04:04 PM   #5
Mikey77T
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Appreciate the write up, and i understand how manufacturers have to target all domestics with one product/design etc.

But my question is, is a performance muffler pretty much a straight through pipe with no baffles etc.?
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      10-21-2019, 04:45 PM   #6
therealdb1
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Quote:
Originally Posted by Mikey77T View Post
Appreciate the write up, and i understand how manufacturers have to target all domestics with one product/design etc.

But my question is, is a performance muffler pretty much a straight through pipe with no baffles etc.?
Depends who makes it. It can be but there are all sorts of possibilities. Gas flow behaviour is a whole science subject in itself. I've worked in the gas measurement industry for over 20 years and I'm still learning things!

You need to decide "what do you want from changing the exhaust?"
If you just want to make more noise you would be better changing the back box.
If you are looking for improved performance you need to look at the whole system as there is little point in changing the front boxes and cats if the gas reaches the rear axle and then gets blocked by a load of baffles and fibre material in the back box.

As aaronblack says you might get a small improvement through the change you suggest but it is unlikely to be noticeable on the road.

You would probably gain more by improving the inlet flow and a remap, for example, giving you more power and the car will feel more driveable and possibly more economical too!
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