Quiet exhaust

[philj]

Needed an exhaust on the S6, wanted it quiet. Can't stand that drone/boom on cruise at peak torque. Also didn't want a 3" exhaust hanging down, the tunnel can't take it nicely. So made a 3" downpipe into a flexi, split that into 2x 2.5" pipes in the hope it wouldn't be such a deep noise, (also have loads of pipe, bends etc still in 2.5", and considering a V8 conversion). First effort was too loud except on boost, this used 2x 4" round by 12" long silencers where the cats were, a 9"x4"x12" middle, and the same rear. Too loud.

I bought a 10"x5"x19" to replace the rear, and 2 3.5"x19" long round silencers to replace the center bits. Probably no lower than stock. Now its alot quieter all round, a touch louder at idle, but still it's a little bit boomy - clearly an aftermarket exhaust.

So my question is, has anyone made a properly quiet performance exhaust? This engine is a loud one. I can't fit anymore silencers in, may be able to get a larger center in, but the whole system would need a rejig.

[AndyP]

Can't offer any advise on the exhaust, but nice work and a great garage!! What's the rat rod?? Any more pics?

[Jamo]

Quiet and performance do really go together as you really need a chamber back box, to this end look at the b5 RS4 back boxes they would give you what you desire

[andy10v]

Did JP not run a big exhaust into a stock backbox for quite a while for good performance and no drone?

[Lloyd]

It took a while and a few iterations to get it sorted, but I run a straight through 3" stainless steel exhaust without any drone. Milltek cat back with a 3" DP and de-cat mini silencer.

1). Try to ensure you keep the original exhaust mounting points in use. This is a bit like using the fret board on a guitar. you don't want a long length of exhaust vibrating freely. Think of the exhuast like a guitar string.
2). Even adding an extra mount can help a lot.
3). If you chop out the cat(s) replace them with a V-Banded straight through mini silencer. This will add back mass to the exhaust at the point where it was set up to be quiet or drone free by the OEM. Effectively dampening down the vibration/drone. The mini silencer will also help a bit to keep general volume levels down.

Chris Tullett recommended this approach and it works great.
Minimal back pressure, nice sound and zero drone or resonance.

[philj]

Tis a great garage, its a friend of mines, the rat rod is a Ford Model (insert letter I can't remember here) He's also done a Hudson which is finished and offends everywhere it goes.

Yeah I did think about a not having straight through boxes, but didn't really want to sacrifice the peformance.

Thanks for the suggestion Lloyd. The exhaust is very well hung, I've got 6 hangers on there. The 2 stock centers, 2 stock rears, and 2 D rubber's which I used to stabilize any vibrations/play, one front under the gearbox, one rear. Definitely not vibrating. All the rubbers are bigger than the old.

My experience with 3" exhausts is they usually have a deeper note and more difficult to silence. Also did not want to sacrifice ground clearance. I've also already did that with the twin 3.5" round 19" long silencers where the cats are.

So you're saying you have a cat back miltek, with an extra silencer where the cat is is drone free? Any pictures of this setup? Rough dimenions of boxes?

[newsh]

Try a labyrinth box instead of a straight through. Or slide some perforated tube up the mid pipes.
Edit: oops cross post

[byd1380]

I worked with my friend and his URS4, he had a 3" system then converted to a 2.7T S4 system, maybe 2x2.25" but was too loud, we tried center boxes, packing back boxes etc. no joy. He managed to buy a Sebring rear box and it shut it up completely.

Ivan

[A1QSHIP]

You might try exhaust tips that angle towards the ground to help with it being too loud.
Chris

[philj]

Cheers, nice to know I'm not on my own. You're both right, I can't really see any other way of making it quieter other than changing the rear box, again. The larger silencers did quiet it down quite a bit but I can't fit enough in to silence it anymore without loosing ground clearance.

Sebring used to make the old AMG exhausts and they always sounded good. I've got a couple AMG backboxes kicking around actually, if not it'll have to be a custom box of 2x2.5", in that size will have an interesting internal design.

[geneandbolly]

i have the OEM audi system on mine and it's completely silent - as in...you have to check the rev counter to make sure it's running!!

[Lloyd]

So you're saying you have a cat back miltek, with an extra silencer where the cat is is drone free? Any pictures of this setup? Rough dimenions of boxes?

Yes, 3" RS2 Miltek catback exhaust -this was cut and fitted properly to the car by Miltek. Out of the box they're a terrible fit around the rear subframe/axle. 3" downpipe with short flexi and V-Band at the end. The DP was originally a forum group buy, but needed several tweaks to get the fit right and allow me to still run the drivers side CV heatshield.

V-Band to either 100 cell race cat (for MOT) or the Chris Tullett re-packable straight through mini silencer. The mini silencer has a bracket which mounts to the original hard rubber/spring gear box mount. I'm only using one side of it as it was originally used for a cat either side. It's then V-Band and 3" pipe directly to the first Milltek box.

The only other thing we added is an additional semi rigid mount about half way under the car. There is a removable bit of narrow folded steel trim which we made into a new additional mount. This is very firm, yet allows the exhuast to expand/contract along it's length - need to find a photo to explain it better.

In short, this setup really does work. Best of both worlds.

[geneandbolly]

any chance of a youtube video to let us hear the new pipes??

[Rusty]

Key to removing the drone is to have a diameter change towards the back axle. I have 3" to rear seats and 2.5" to a single back box and it's silent on a cruise.

[philj]

The Miltek has very large boxes from what I can find, also I don't think the rear is a straight through design.



Will try and get a video.

Cruise noise usually depends on where your peak torque is, if you have a larger turbo, cams etc it'll shift the drone to higher in the rpm range. Which would be fine by me. 2k brraaaa is not. Don't really want to step the size down, but nice to know it works.

Found a few other solutions....







Google - Noise Canceling Chamber/helmholtz resonators/reactive silencer