1M drone fix with mid pipe swap?

[werman]

Hello to all! I purchased a 1M a few weeks ago and love it.

I think the stock exhaust system sounds great with the exception of significant drone in 6th gear on the highway.

One of the threads I've perused has pictures which suggest that the resonator on the stock 1M mid pipe is hollow (thus non-functional) and that this might explain the droning.

What I'm thinking of doing is swapping my stock 1M mid pipe for a N54 mid pipe harvested from a 135i. My research suggests that the resonator is functional on the 135i mid pipe and that this might help with the problem.

I've considered the N55 mid pipe but the comments regarding unpleasant odors and very loud start-up volume are steering me away from this swap.

I would be interested in comments on my proposed plan or other suggestions regarding reducing/eliminating drone. I've upgraded the "flat storage compartment" (under the hard trunk liner in front of the battery compartment) with some Dynamat and Luxury Liner Pro and it has helped a bit but the drone persists.

Thanks and I'm excited and happy to be a member of the 1M community!

[iDontRemember]

I have the N55 midpipe, I don’t notice any extra smell.

Slightly louder upon cold start.
The drone has moved to the 3k RPMs area and is a different tone.
The exhaust note is improved.
Power delivery is smoother.
Small weight savings.

Overall a great change except the DP to midpipe bolts all snapped off and I had to drill them all out.

[nachob]

Originally Posted by werman

Hello to all! I purchased a 1M a few weeks ago and love it.

I think the stock exhaust system sounds great with the exception of significant drone in 6th gear on the highway.

One of the threads I've perused has pictures which suggest that the resonator on the stock 1M mid pipe is hollow (thus non-functional) and that this might explain the droning.

What I'm thinking of doing is swapping my stock 1M mid pipe for a N54 mid pipe harvested from a 135i. My research suggests that the resonator is functional on the 135i mid pipe and that this might help with the problem.

I've considered the N55 mid pipe but the comments regarding unpleasant odors and very loud start-up volume are steering me away from this swap.

I would be interested in comments on my proposed plan or other suggestions regarding reducing/eliminating drone. I've upgraded the "flat storage compartment" (under the hard trunk liner in front of the battery compartment) with some Dynamat and Luxury Liner Pro and it has helped a bit but the drone persists.

Thanks and I'm excited and happy to be a member of the 1M community!

Welcome. IDontRemember does a lot of work on his car and is a great resource. I wish you were closer so I could listen to your drone. I have heard of such a thing. I have owned two 1M coupes, one brand new since .3 miles to a used one starting at 9K miles. I have test driven countless ones and there is a slight "drone" but I never heard a stock one that was objectionable though I have heard about it for years. Are you sure yours is all stock and it hasn't been modified? It could also be that the "drone" just isn't uncomfortable to me too. I know certain sharp sounds are painful to me. Sometimes my daughter even cackles laughing and it can hurt so I can see that certain frequencies can affect people differently but anyway, since you got yours used, just wonder if it really is all stock? Some of these cars have gone through 3-5 owners and one might not even realize it.

Welcome and best of luck.

[MechE]

From new, my stock 1M had a drone around 2,100 rpm at part throttle. It spanned a region of approximately 400 rpm and could become annoying on long gradual uphill sections of road. The n55 mid-pipe slightly reduced the volume of the drone and reduced its rpm band to approximately 200 rpm. With stock down pipes, the n55 mid-pipe did not create any unpleasant odors. Installing a Dinan axle back exhaust with the n55 pipe basically eliminated the drone. I now have the full Akrapovic Evolution exhaust, which has no drone. Furthermore, in quiet mode the Akra. exhaust is arguably quieter than stock.

Welcome to the 1M community...

[CarJunkie]

My MadDad midpipe also reduced the drone's relative volume and narrowed the rpm band. Addition of Lightweight Ti rear section took it away almost completely, but I still hear it occasionally on long uphill sections.

[ayao]

My experience was:
-the stock midpipe drones at highway speed
-N55 midpipe drones a little bit less but you will notice it if you are sensitive to these things -- MechE's description above is spot-on
-Maddad midpipe and Remus axleback does not drone, but it is noticeably louder than the stock setup

[werman]

Thanks to all for the insight! All of the comments are helpful.

I'm still leaning towards harvesting a stock N54 mid pipe from a 135i if i can find one, assuming that it will have a functional resonator. I don't see any complaints about drone from owners with the 135i performance exhaust and my hope is that this could be a cost-effective solution.

If I can't find one of these, I might purchase the N55 mid pipe after reviewing the information from the above posts. I could always consider grafting my 1M catalytic converters to the N55 mid pipe if I find the volume or smell objectionable but it sounds like I might be OK.

I will definitely let the group know of the results. I'm still open to other suggestions and comments. Thanks again! This community is fantastic!

[ayao]

Originally Posted by iDontRemember

I have the N55 midpipe, I don’t notice any extra smell.

Slightly louder upon cold start.
The drone has moved to the 3k RPMs area and is a different tone.
The exhaust note is improved.
Power delivery is smoother.
Small weight savings.

Overall a great change except the DP to midpipe bolts all snapped off and I had to drill them all out.

While I hope it never happens to me, how did you manage to get anything substantive in there to drill out the studs / bolts?

[FIRSTM]

Originally Posted by MechE

From new, my stock 1M had a drone around 2,100 rpm at part throttle. It spanned a region of approximately 400 rpm and could become annoying on long gradual uphill sections of road. The n55 mid-pipe slightly reduced the volume of the drone and reduced its rpm band to approximately 200 rpm. With stock down pipes, the n55 mid-pipe did not create any unpleasant odors. Installing a Dinan axle back exhaust with the n55 pipe basically eliminated the drone. I now have the full Akrapovic Evolution exhaust, which has no drone. Furthermore, in quiet mode the Akra. exhaust is arguably quieter than stock.

Welcome to the 1M community...

I agree, drone around 21-2500 rpm, with n55 mid drone mostly gone, I love the cold start with it and no smell so far, installed it about 9 years ago.

[iDontRemember]

Originally Posted by werman

. If I can't find one of these, I might purchase the N55 mid pipe after reviewing the information from the above posts. I could always consider grafting my 1M catalytic converters to the N55 mid pipe if I find the volume or smell objectionable but it sounds like I might be OK.

This would be bordering on pointless.. the secondary cats are the big difference between what you have, the n54 midpipe and the n55 midpipe.. You'd essentially be making another n54 midpipe. the n55 has a small resonator in the Y second before the muffler.

Originally Posted by ayao

While I hope it never happens to me, how did you manage to get anything substantive in there to drill out the studs / bolts?

Once you remove the midpipe, the downpipe studs are easily accessible.

[werman]

Originally Posted by iDontRemember

This would be bordering on pointless.. the secondary cats are the big difference between what you have, the n54 midpipe and the n55 midpipe.. You'd essentially be making another n54 midpipe. the n55 has a small resonator in the Y second before the muffler.

I appreciate the experienced help with this potential project.

My thinking is that the only difference between the mid pipe on the 135i (no drone) and the one on my 1M (which drones) is the fact that the 135I has a functional resonator. If the N55 mid pipe has a functional resonator then I'm essentially duplicating the mid pipe on the N54 135i by grafting the functional resonator of the N55 mid pipe to my 1M mid pipe catalytic converters.

PLEASE correct me if I'm faulty on any of this reasoning as I really don't want to embark on a fruitless endeavor.

Again, a sincere thanks to all for helping me with this!

[iDontRemember]

Originally Posted by werman

I appreciate the experienced help with this potential project.

My thinking is that the only difference between the mid pipe on the 135i (no drone) and the one on my 1M (which drones) is the fact that the 135I has a functional resonator. If the N55 mid pipe has a functional resonator then I'm essentially duplicating the mid pipe on the N54 135i by grafting the functional resonator of the N55 mid pipe to my 1M mid pipe catalytic converters.

PLEASE correct me if I'm faulty on any of this reasoning as I really don't want to embark on a fruitless endeavor.

Again, a sincere thanks to all for helping me with this!

Possibly, you also have to consider that the muffler design is totally different on both and i'm sure some "extra sound" was engineered in on the 1m.

I've considered getting a couple of inline resonators but that would involve me not being lazy. Not only that, the sound during acceleration and WOT is music to my ears

[Em/1]

I agree with moderate drone stock at 2100-2500, part throttle. Much better after catless DP; no smell cuz still have the midpipe. No codes with Cobb at least; passes inspection no prob in IL. Did I mention the extra HP and mild increase in volume (mostly at start-up, which I happen to like!)

[werman]

I did it! I purchased an OEM lightly used mid pipe off of a 135i with the N54 engine. I swapped my OEM 1M mid pipe for it. The 135i mid pipe has the secondary catalytic converters and what I'm assuming is a functional resonator. The drone is pretty much gone. Start-up is a bit less noisy, too. I really don't notice any difference in the character or volume of the exhaust note while actually driving the car and I don't notice any difference in the power band either.