Possible exhaust drone solution...

[merlin's S4]

Stole this link from a discussion on quattroworld.com

http://www.performancetrucks.net/forums/gm-engine-exhaust-performance-21/how-build-exhaust-resonator-tube-eliminate-drone-489463/

Link to quattroworld discussion

http://forums.quattroworld.com/s4s6/msgs/188779.phtml

[Rusty]

My exhaust drops from 3" to 2.5" just before the rear subframe and doesn't drone at all, even though it's a single box system!

[Lloyd]

Exhaust drone (resonance) is often due to a poorly supported or fixed (damped) exhaust system. Think of a guitar string humming.

To reduce the drone (possibly eliminate it) you need to improve or add additional exhaust mounts. For example, you probably have a non OEM exhaust system. Have you continued to use all of the original exhaust mounting points?

If you have, you can stiffen up the existing rubber bungees and even add an additional mount, fix the exhaust to the chassis half way between the longest unsupported run. Think again of that guitar string humming and you then put your finger halfway along the fret board. The note changes right?

As you beef up the mounts and/or add more mounts the rpm that you get the drone will tend to drop lower and lower rpm and get quieter. With luck, the drone will disappear outside of the excitation range.

I've got a 3" DP and Milltek system with a decat pipe. I had to do all of the above and finally add a small straight through silencer in place of the decat pipe to get it quiet.

HTH

[Sleeper_Avant]

leave the car in the garage?

sorted

[driftin jo]

There is already a good solution to exhaust drone, its called WOT.

[Billman]

I have a drone problem with these dual 60mm RS2 exhaust from BN-Pipes. From 2400-2900 it is awful. The rest is great :-D

I used the original mounting points.

[Billman]

I have a drone problem with these dual 60mm RS2 exhaust from BN-Pipes. From 2400-2900 it is awful. The rest is great :-D

I used the original mounting points.

According to this like I need a pipe 76cm long! A bit much for under the car.

And what about performance? Doesn't it cause worse flow?

[Lloyd]

I have a drone problem with these dual 60mm RS2 exhaust from BN-Pipes. From 2400-2900 it is awful. The rest is great :-D

I used the original mounting points.

I bet that's fun in and around town. What flywheel are you running? I had major resonance around that RPM when running a lightweight Spec Aluminium and un-matched (balanced) flywheel. I changed it for an OEM 3B steel flywheel that I had lightened and then balance matched to my OEM Dual Mass flywheel. Resonance now gone. All I have left is what I expected, short bit of gearbox chatter.

Here are some photos of the additional exhaust mount fitted to my car to damp out the resonance... The bracket it's bolted to it already on the avant - it's just part of the prop cover which really was doing nothing in particular. Now it's a handy place to fix the exhaust via some rubber bobbins.

The exhaust is free to move fore and aft within the bracket as it heats up, cools down etc

[Billman]

Town is not a problem! Low speed cruising with closed windows is crap!!!

@Lloyd

does it helped?

[Lloyd]

Town is not a problem! Low speed cruising with closed windows is crap!!!

@Lloyd

does it helped?

What flywheel are you running?

[Billman]

I am using a lightened 7A one balanced to 0 by Aelred. I have a 6 pad sintered clutch and alot of gearbox chatter. but the drone comes after the chatter and had it also before the flywheel/clutch change with the stock adu dual mass.

[Lloyd]

I am using a lightened 7A one balanced to 0 by Aelred. I have a 6 pad sintered clutch and alot of gearbox chatter. but the drone comes after the chatter and had it also before the flywheel/clutch change with the stock adu dual mass.

If the drone was present before the flywheel change, when you were running a dual mass flywheel, I would only suggest you try adding one or more stiffer exhaust mounts.

I found adding the above extra exhaust mount and changing from the Al flywheel to a matched & balanced steel flywheel solved all of my resonance issues. I know how bad it can be so wish you luck in solving it.

[Billman]

BN-pipes was aware of the problem and they offer a service (at extra cost) to change one of the mufflers but you have to send the exhaust back for modification. I am not willing to do it.

[dobbin]

audi rs2

i fitted a 3" down pipe refitted original cat and 3" pipe with one large silencer and 1 small one at the back , but fromm 3000rpm upwards ie on the motor way the noise is
unbearable after a time . been back yesterday to welsh coast customs in newport and he has ordered from the states a 3" resonator pipe which he says will cure this problem.
i will let you know how i get on.

[Tzummie]

I have exactly the same problem with the BN pipes on my (completely standard/bone-stock) RS2; Right between 2.000 and 3.000 RPM the resonance in the cabin is quite unbearable (especially taking the family in the RS2 to Spain for 3200km to/from...); For my profession, I've used the 1/4 wave solution many times, to solve resonance issues in (reflex-loaded) speaker cabinets ("vent muffler"). But here the range is quite wide and not at a specific rpm.

@ Billman: What was the solution BN suggested? What was the cost involved? I have also a small weld problem, as the pipe is not sealed.

thnx.