Just installed the NM engineering downpipe back exhaust on my 2012 Cooper S hatchback.

This exhaust is everything one would would expect as far a fitment, quality, etc., very well made. Absolutely simple and straight forward to install. Bolts right up with no fitment issues. Overall sound and disposition of the exhaust is perfect, other than what is mentioned below. I really want this exhaust to work, I like it that much!

The only major issue has been this horrible whistle-like resonance upon hard acceleration (see video link).

Just some background info: I have installed and removed probably 20+ exhausts from MINI's over the last 10 years, so I kind of know how to do it. Even with that experience, I re-installed this NM system three times to make sure I wasn't missing anything that would cause this loud whistle resonance.
I am confident the exhaust is correctly installed.

Of course, I will chat with NM Engineering once the holidays have past and see if there is an easy resolve, but for now I would like to see if anyone else is dealing with this issue and also give a good video example of the problem for comparison.

I am concerned it is an issue with the muffler design itself because I did find one other post with the same issue, but he had the Cat back only design, which would mean the down pipe attachment joint/seal never came into play: https://www.northamericanmotoring.co...t-5k-rpms.html
I also pulled the rear NM muffler section and just ran the first section pipe that attaches to the stock down pipe and did NOT get the whistle resonance, so that leads me to believe noise is in the muffler section then resonates through the whole system. However the car is freaking loud when run straight pipe and back pressures have changed, etc. so not sure how conclusive that can be. Anyway hoping for an easy fix.

VIDEO: http://www.youtube.com/watch?v=hW9ZU2EU53M

 

I posted a thread about this a while ago and found no real answers. The local MINI club calls my car the Whistler and it pretty much stuck.

You can read about my experiences here:

https://www.northamericanmotoring.co...ml#post3426398

My car sounds exactly like yours in the video at 5300 RPM. I had three MINI Techs drive my car and we found no reason for the sound. All the flanges were tight, rechecked and tightened again.

NM claimed they never heard of that before, yet yours is the 4th video I have seen of it. NM speculated that due to it only occurring at WOT (in my car) that it must be air rushing past a corner or burr inside the muffler acting like a whistle.

I actually have grown to like the whistle as it is my calling card. When we were at a couple club runs we went through a long tunnel and I had that baby screaming through there. I have been told it is very loud outside the car when I am ripping up the road.

 

I've never heard that on the NM exhaust, but I have heard that exact same sound on the Quicksilver exhaust.
I've also thought this sound could be from the flanges/joints not lined up exactly straight. It's easy to move around the flanges and see if it changes.

 

Yeah, hence the three re-installs, trying to move things around a bit. No change whatsoever. Fact is, the darn thing lines up so easily it is hard to mess it up. I have dealt with exhausts that are complete fitment nightmares from the get go, this one is easy. I am hoping it is just a one or two off problem and we don't see further issues. Dig the exhaust overall, but definitely not going have it whistling away like is does now.

 

That sound would drive me nuts. I don't think I would be satisfied with that as obviously you are not.

I hope you can eventually find the cure. It's quite easy to hear and does not sound "normal".

 

lol my suspission is since this only happens with dp back exhausts is that the aftermarket flange lip creates the whistling.

 

My car has the cat back system and it has done it from day one. After we went to the Dragon and came back with about 1500 miles on the exhaust it has so much pop and burble while coasting its insane. To the OP....wait till it breaks in and sounds really deep and throaty and see how many heads it turns. I understand you may hate the whistle, but mine only does it when I mash the gas pedal all the way to the floor and hold it there past 5300 RPM, which I hardly ever do during normal driving. I can make it whistle at will, so I just live with it.

 

DP back is the specifics here. Do you have a DP back from cut from the second cat?

 

My car has the muffler that installs by cutting the pipe just in front of the cat that is under the rear of the car. I didn't buy the more expensive kit that replaces the down pipe from the engine down, and then goes all the way back.

 

You wont hear what the OP is talking about here are examples im sure.


Listen at hi rpm you will hear the high pitch squeal


http://www.youtube.com/watch?v=qB1lPWpvCI0

http://www.youtube.com/watch?v=OaXKQe-0UVU

 

BigPrfed.....I am confused by your post. I DO hear what the OP showed in his video and I was explaining my car does the EXACT same thing. I dont have any videos of it but I can try to post some this weekend. If you look up to my original response there is link to a thread where I documented all my experiences with trying to figure this out.

It is a distinct loud marmonic resonating sound that is similar to a loud whistler....hence my cars name.

My car sounds nothing like those two videos....mine is like a train whistle and can be heard from over 100 yards away, as described by my neighbors.

 

lol touche... i posted in that thread too hahaha dummy me. My apologies i should have read more. I thought he was referring to the high pitched squeal

 

I have an NM cat back on my 2011 MCS. It has the same whistle/scream as the others. I have taken it back to the installer looking for leaks and to the dealer. Nothing is wrong. Like our other NC native, Whistler, I have come to enjoy the scream. Our 2011s do "over boost". Could it be the blowoff valve?

 

its not blow off, two seperate systems.

 

Here is a follow up video with the third, most rearward muffler section, of the exhaust removed.

You will notice no whistling at all. Being that the whistle noise is in the cat back and down pipe back versions of this exhaust, I am highly confident the muffler section is causing the problem.

NM Engineering has been super helpful, and ultimately will take care of any concerns about this whistle noise, but because it is such a promising exhaust (not many down pipe back solutions out there), I thought I would kick in some effort and see if we can find solution, so we are working on that now. More to come...

VIDEO: http://www.youtube.com/watch?v=jrSzdIyy-lk

 

Would like to hear from NM on this as their exhaust was on my short list until now. That whistle would drive me bonkers.

 

That is odd. I just installed my NM DP back system back in November. I haven't heard anything like that. Did you use the included gasket on between the second and third piece? hmmmmm?

 

Gasket used and no leaks. What is interesting is the only ones with scream/whistle are 2011 and 2012 MCS including the OP.

 

Mine on my 2011 MCS is still behaving....been tryin' to make it squeal. I even yell at it....SQUEAL! Squeal like a ..that's enough.

 

So I built a new third section for the NM engineering down pipe back exhaust system, which I had planned to do anyway, before this whole "whistle" issue came up.

This new third section is just a straight pipe, without the muffler, for use on the track. I used the same flange and gasket the came with the NM system, so everything the same minus the muffler. Absolutely no whistle at all with the new set up. I am 99.9% sure that the problem lies within the muffler section at this point. I don't know if some mufflers manifest it and others don't, or if is is related to the newer cars in combination with the muffler, etc. etc. But what I do know, is when I get rid of that third section, the whistle is GONE.


VIDEO: https://www.youtube.com/watch?v=gntN...eature=related

 

Glad to see this info. Had plans to order the cat back version today for my 2008. The cat back was out of production/stock for a while until just recently. Wonder if NM did some sort of fix or redesign. I'll have to give them a shout in the am.

 

How can you do an exhaust video without letting us hear the exhaust?

 

I have yet to shoot the video, of course...

Here is one inside the garage with the muffler delete, in sport mode, burbling and crackling away. The sound is over emphasized in the confines of a closed garage, so it is not totally realistic, I shot this video mainly for fun, so don't take it too seriously. It actually sounds pretty good when driving... perfect for hearing the shifts/rpms with a helmet on for the track. I'll post some driving footage soon.


Video: http://www.youtube.com/watch?v=P13zGkH9xr4

 

Just a note on NM engineering: they have been nothing but fantastic in working with me on this issue. The exhaust is top notch and really well made. You have no worries if there ends up being a legitimate issue, which in my opinion, is the case...

 

I wonder if you put some thin wire right before the muffler to disrupt the air flow a tiny bit would help at all? Obviously this would just be a band aid and not a real fix. This defiantly leads me to believe that it's the baffle design of the muffler.

Very detailed right up and I hope it works out, the car sounded great.