[max_330i]

Last week, a local muffler shop chopped my factory muffler and welded in a straight pipe with a set of 3.5 inch dual tips. The car sounds amazing at most speeds around town, however when I go WOT above 4500 RPM or so, I'm getting a strange whistling noise from the rear of the car. Reference videos in this thread for an example of the sound: http://www.e90post.com/forums/showthread.php?t=309325

When I first noticed this I immediately checked all the welds, and found nothing to complain about; the muffler shop did a nice job. But I think the issue is the tips. My stock 330i muffler had two exhaust tips coming off the muffler, but my straight pipe has a Y-pipe style dual tip, basically like this:



Those of you with muffler deletes, have you encountered this kind of problem? My gut feeling is that air hits the Y-pipe dual tips at an awkward angle, causing the sound. I'm thinking of going back to the shop and asking the guys to chop the dual tips and weld in a larger single tip to see if that fixes it. If there's something else I should consider before the nuclear option, I would appreciate the insight.

[terryd5150]

I have muffler delete on an E92 335i; it does not make a whistling sound.

[Welcome to NBA Jam]

[mike-y]

first thing that popped in my head when I read the title of the thread.


"..and the whistles go WOOOOOOOOOO"

[djh2]

Originally Posted by mike-y

first thing that popped in my head when I read the title of the thread.


"..and the whistles go WOOOOOOOOOO"

I thought the same thing and considered linking a video.

OP - When you say you checked the welds, you mean on the inside of the pipe, correct? Or did you just look for holes. I am suspicious that there may be a sharp edge or burr on the inside.

Another thing you could try is temporarily plugging one side of the tip. This would change the flow pattern and might show the issue

[max_330i]

Originally Posted by Welcome to NBA Jam

I knew this was coming eventually.

Originally Posted by djh2

I thought the same thing and considered linking a video.

OP - When you say you checked the welds, you mean on the inside of the pipe, correct? Or did you just look for holes. I am suspicious that there may be a sharp edge or burr on the inside.

Another thing you could try is temporarily plugging one side of the tip. This would change the flow pattern and might show the issue

I tried something I read online. I sprayed some soapy water on the areas where the pipes were welded and had somebody else rev the car while I looked under, and didn't see any bubbles coming from the welds, so I figured there is no exhaust leak. How do I look for a sharp edge on the inside?

I will have to block one of the tips and see if it makes a difference.

[matt@supremepower]

Had this happen to me back when I had a 328i. Its not the outside welds, but the inside of the tips. Where the tip is welded onto the exhaust, but on the inside. Hard to explain but have them weld the area INSIDE the pipes where the single exit side of the tips meet the exhaust piping.

To test it, have the muffler shop cut the tip off and see if the whistling continues. If it goes away, they just need to weld the inside of the tips then reinstall the tips.

[Eddien123]

Same thing I did to my car. axel back is straight piped. 3.5 inch dual tips. No whistle.