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      10-15-2018, 12:25 PM   #1
TheCoolX3
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Air rushing noise from catless downpipe

I installed the VRSF downpipe a few weeks ago and have heard this high pitch air rushing sound since I have installed it. I've listened to videos of other N55s with the same set up (Catless DP & stock cat back) and they do not make the same noise at all. I have replaced the turbo gasket and the Vband clamps are next. What baffles me is that this sound only persists for about 10-20 seconds until the engine revs down from the cold start. It also makes a pretty horrible 'turbo spool' noise while driving under light to medium throttle only in Comfort Mode (may be tune related) then again, I have heard no other N55s make.

Looking for any suggestions/Advice

Video link:


My apologies, I am not sure why the video looks like I recorded it on an Ipod Shuffle
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Last edited by TheCoolX3; 10-15-2018 at 01:10 PM..
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      10-15-2018, 05:51 PM   #2
doodlebro
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On cold start, the wastegate pops open to heat the cat faster. I think you're just hearing that... Shouldn't be any great concern as long as it doesn't get worse/happen at other times.

You can turn cat heating off with bootmod3, but I leave it on cause it sounds great!
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      10-15-2018, 05:53 PM   #3
TheCoolX3
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I experimented with turning it off and it just sounds dumb. Any thoughts on why this is happening to my x3 and not others with the same mods?

Quote:
Originally Posted by doodlebro View Post
On cold start, the wastegate pops open to heat the cat faster. I think you're just hearing that... Shouldn't be any great concern as long as it doesn't get worse/happen at other times.

You can turn cat heating off with bootmod3, but I leave it on cause it sounds great!
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      10-15-2018, 05:58 PM   #4
doodlebro
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I think the other drivers are turning cat heating off.

In a couple of weeks I'm installing my VRSF catless, so I will be able to confirm this.

But I do think it's normal/expected if you just hear it until it revs down. Basically, the car optimizes flow through the cats during startup to get them warmed up quicker. It's an efficiency thing. I think you're just hearing the lack of back-pressure from the primary cats, since you've removed them.
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      10-15-2018, 06:28 PM   #5
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Have you tried/experimented with cold start delete?
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      10-21-2018, 07:41 PM   #6
TheCoolX3
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I believe this sound to be the infamous waste gate rattle that N55 PWGs suffer from. However it does not sound like a rattle or clicking but an air rushing noise.

Was gonna try using heat wrap to quite or kill the sound - Will post back with results.

Will also play with cold start delete.

Any other suggestions?
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      10-23-2018, 01:27 PM   #7
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Sounds like waste gate rattle from the cold start. Do the cold start delete. My car makes this sound, though not as loud, since I still have my cat still
installed.
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      10-23-2018, 02:40 PM   #8
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I am fbo and have the vrsf race cat which sounds just like this. I don’t think there is an issue personally. But videos never do justice when trying to diagnose sounds. GL

Last edited by Victoracer; 10-23-2018 at 04:31 PM..
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