Let's talk about drone and custom exhausts

[epiphanyray]

So, I have been meaning to post this for a few days now...

I had received my new-to-me 2013 M5. Loved everything about it, except the sound. I am coming from 2003 M5 with Dinan Exhaust and love everything about it.

So, I spoke to a friend who has done some exhaust work for other F10 m5s. He told me he would make a custom exhaust for me that would make the car sound A LOT better yet not obnoxious at all.

So, he cleanly cut the OEM exhaust, and put in what seems to be some sort of resonator instead. Don't get me wrong, the car sounds AMAZING. Not obnoxious at all, and absolutely PERFECT. Everything I wanted. it sounds like a TRUE M Car and 4 inch exhaust tips just like I wanted.

THE PROBLEM:

Simple. The Car drones at 1500-1900 RPM. If I am cruising on the highway doing 70-80mph at 7th gear, I find myself going into 6th gear on purpose, just to keep the RPM right above 1900. Anything outside 1500-1900 RPM is dead Silent like stock.

I dont know much about this, but the simple question is... Can I keep the sound as is and somehow LOSE this drone? The wife hates it, and I am growing sick of it. I've heard about sound deadning material between exhaust and chassis / rear trunk (DYNAMAT? )

I really don't want to go back to my OEM exhaust....

Thoughts?

Here are a few pics of the OEM exhaust as it was cut, and the new setup.

[brad850csi]

Have you disconnected the ASD box?

[epiphanyray]

Originally Posted by brad850csi

Have you disconnected the ASD box?

Yes I disabled ASD via coding a couple weeks ago.

[mister2d]

Originally Posted by epiphanyray

...I had received my new-to-me 2013 M5. Loved everything about it, except the sound. I am coming from 2003 M5 with Dinan Exhaust and love everything about it.

Funny. I came from the same E39 with Dinan Exhaust. That exhaust was underrated from a sound standpoint. It was absolutely perfect for that car.

Originally Posted by epiphanyray

THE PROBLEM:
...
Anything outside 1500-1900 RPM is dead Silent like stock.

I disabled ASD and took out the stock resonators to replace it with 3-inch pipes. With the windows up my car sounds almost dead silent as stock too. This is the only thing frustrating with this car. My 4L twin turbo AMG had WAY more rumble and organic noise with no drone. What did BMW do to these cars?

[epiphanyray]

Originally Posted by mister2d

Funny. I came from the same E39 with Dinan Exhaust. That exhaust was underrated from a sound standpoint. It was absolutely perfect for that car.




I disabled ASD and took out the stock resonators to replace it with 3-inch pipes. With the windows up my car sounds almost dead silent as stock too. This is the only thing frustrating with this car. My 4L twin turbo AMG had WAY more rumble and organic noise with no drone. What did BMW do to these cars?

NO IDEA... Im super frustrated with this drone in that RPM Range! Do you still have the e39?

[apexlocator]

Here's the simple solution that you may not want to hear...get rid of that setup. Been there, done that (Turner deletes). Yes, the drone is not bad if its not your daily driver and you dont drive family around. Yes, it sounds amazingly awesome outside of that RPM range, but cruising speeds will almost always end up in that drone zone....highways, parking lots, etc. It will gnaw away at your patience little by little, but worse, at your wife's patience lol.

[epiphanyray]

Originally Posted by apexlocator

Here's the simple solution that you may not want to hear...get rid of that setup. Been there, done that (Turner deletes). Yes, the drone is not bad if its not your daily driver and you dont drive family around. Yes, it sounds amazingly awesome outside of that RPM range, but cruising speeds will almost always end up in that drone zone....highways, parking lots, etc. It will gnaw away at your patience little by little, but worse, at your wife's patience lol.

Been dreading that response.... But I had a feeling.

So,I guess modify oem exhaust to fit my tips and be done with it? Maybe keep valves open to keep a little bit of that Rumble?

[josec70]

If you want some more rumble and no drone there are many axle-back / cat-back options that will provide a deeper exhaust note with zero drone (Akra, AWE, Eisenmann etc.). Not the best bang for your buck but you can certainly attain nice exhaust tone w/o drone. Some nice systems for sale on the classifieds.

[mister2d]

Originally Posted by epiphanyray

Been dreading that response.... But I had a feeling.

So,I guess modify oem exhaust to fit my tips and be done with it? Maybe keep valves open to keep a little bit of that Rumble?

Depends on the oem modification. I get drone with no resonators, the valves open, and windows down in that rpm range. Nauseating.

I'll consider AWE or Magnaflow the next time I revisit the exhaust. For now, those valves are back to not being forced open and everything is fine.

[apexlocator]

I had settled on the AWE catback when a used set of Corsa/Turner mufflers listed in the classifieds....cant go wrong with those. I thought it too quiet at first, but it does open the ears in the high RPMs, and since going catless, its just right at lower RPMs, but with that crackling roar at high RPMs, characteristic of a catless setup.

[epiphanyray]

Originally Posted by mister2d

Depends on the oem modification. I get drone with no resonators, the valves open, and windows down in that rpm range. Nauseating.

I'll consider AWE or Magnaflow the next time I revisit the exhaust. For now, those valves are back to not being forced open and everything is fine.

So if I put the oEM exhaust back on, and keep the valves open, I will still experience drone?

So I guess the valves are the ones that keep this under control?

[mister2d]

Originally Posted by epiphanyray

So if I put the oEM exhaust back on, and keep the valves open, I will still experience drone?

So I guess the valves are the ones that keep this under control?

I'm unsure about that. I don't have the stock resonators any more that's why it drones for me. Sounds like you still have them. You might be just fine.

[allmotor_2000]

if you want to eliminate the drone, you need 1/4-wave resonators. I designed this on my previous car... full straight-thru system

[epiphanyray]

Originally Posted by allmotor_2000

if you want to eliminate the drone, you need 1/4-wave resonators. I designed this on my previous car... full straight-thru system

OK... Soo pleaseee tell me more.

1/4 wave resonators? Where to buy? How should they be welded on to current pipes... Does it matter where they are welded on?

Excuse my ignorance, but im super interested

[allmotor_2000]

Originally Posted by epiphanyray

OK... Soo pleaseee tell me more.

1/4 wave resonators? Where to buy? How should they be welded on to current pipes... Does it matter where they are welded on?

Excuse my ignorance, but im super interested

Yes - you have to cancel out the drone frequencies by installing a capped tube (per bank). The length of the tube depends on the frequency (based on RPM) of the drone. The tube needs to come off the main exhaust path at 90-degrees. Lower the drone RPM, longer the tube...

They are just capped tubes... so you don't buy them. Need a fabricator to make them.

I had calculated this for various RPM's and the resulting tube length.

[epiphanyray]

Originally Posted by allmotor_2000

Yes - you have to cancel out the drone frequencies by installing a capped tube (per bank). The length of the tube depends on the frequency (based on RPM) of the drone. The tube needs to come off the main exhaust path at 90-degrees. Lower the drone RPM, longer the tube...

They are just capped tubes... so you don't buy them. Need a fabricator to make them.

I had calculated this for various RPM's and the resulting tube length.

Why do you have two sets of data? One for BANK 1 and the other for Bank 2? If my drone happens mostly between 1600-1900 RPM, does this mean that I should make two tubes (1tube = 32.8inches and the other 28.1 inches)?

Shouldn't both tubes be the same length?

[allmotor_2000]

Originally Posted by epiphanyray

Why do you have two sets of data? One for BANK 1 and the other for Bank 2? If my drone happens mostly between 1600-1900 RPM, does this mean that I should make two tubes (1tube = 32.8inches and the other 28.1 inches)?

Shouldn't both tubes be the same length?

Only difference is the speed of sound value. Exhaust is hotter so speed of sound increases over temp. Use the higher value (top table). Same on both sides....

[apexlocator]

Those look like helmholtz resonators employed by some aftermarket exhaust systems. I see them mostly in the JDM market...

[epiphanyray]

Originally Posted by allmotor_2000

Only difference is the speed of sound value. Exhaust is hotter so speed of sound increases over temp. Use the higher value (top table). Same on both sides....

So two 32.8 inch long, sealed on both ends, hollow pipes. I make a hole in the main pipe (bank 1 and 2), and weld this on there at a 90 degree angle? like this (view crappy drawing) and image.

what diameter should these pipes be? 3? 4 inches?

[evilb]

This is really cool info. Subbing.

[epiphanyray]

So I found this:

and this:

Pretty much exactly what allmotor_2000 is saying.

[epiphanyray]

The video states to make sure the resonators are as close to the engine as possible so that it cancels the frequency as quickly as possible.