Looking for drone-free solution for my 1.8TQ Avant with GTRS

[eljay]

So, I am looking for a permanent solution for my exhaust that has two issues in my books:
- bad drone at 3k on highway (hard to even have a conversation in the car and rear passengers are complaining)
- the flexpipe is the lowest point under the car (looks like it's about 4"-5" off the ground). Plus the flex joint looks like it will need to be replaced soon.

It's a custom exhaust done by the previous owner, not my doing. Here's the setup:
3" test pipe into a 3" downpipe into a Magnaflow cat (2.5" in/ dual 2.25" out) then into 2.5" pipes with a resonator on each into a Magnaflow muffler with a 4" tip on each side.

The exhaust used to have a big center muffler (droned just as bad with it) and when it developed a hole, I replaced it with the cat, which I found out is pointless since I don't have SAI and the Maestro tune has the emissions tuned out as I don't have a CEL.
I don't want to be spending money on it, but it's driving me nuts.
Is there a "simple" solution for the drone? I've read some success with a side resonator (helm-holtz). Or should I just stop patching the issue and get something like the OBX catback exhaust and replace the whole thing? I've read that it does not drone.
Please don't tease me with Milltek or APR as they are too much for me. I can barely afford the OBX if that's a solution.

Thank you for any pointers. GTRS owners' input would be great.

Added pics of the setup:

[Fast4esT]

I'm really surprised you are having a drone issue, I have the same setup as you basically but I have a test pipe and magna flow mufflers, no car, no resonators. Mine drones at 55 some, it's very bassy, but at 60 it's quiets down a lot. I also noticed it get quieter when I added the frankenturbo exhaust manifold.
Have you confirmed you do not have any other exhaust leaks?

[Rus_ninja]

Look into Borla, old guy has it, have not heard him complain about drone. I have Almost the same setup as you and I do get a little drone around 1.8 - 2k after that it smooths out. I have no clue what your problem could be, maybe as mentioned above, check for exhaust leeks.

[Steve Bassen]

Get a used S4 catback and add a y-pipe to your mid-pipe to fit it...

[hgtuner08]

Im not sure as to the validity of this but you can try checking to see if its a resonant frequency issue. Basically when you hear the droning crack the windows slightly or open the sunroof. If this seems to alleviate the issue, you can try dynamatting the trunk and under the rear seat. I did this but it didn't make a huge difference for me. I have an AWE exhaust with tt downpipe and test pipe and it gets pretty loud. I think im gonna try dynamatting the under the rear seats to see if that helps, I think that might be the trick. There is some discussion as to the best sound deadening material, check out some of the alternatives to dynamat, fat mat comes to mind.

[eljay]

Thanks for all the input guys. I'm pretty sure I don't have leaks. When I did seafoam the intake, there was only a tiny bit of smoke from the engine bay by the exhaust manifold. It was very small. I have added the pictures of what I have there. So, it looks like I will be replacing the flexpipe soon and that cat in the middle is probably not doing much and just restricting the flow, so after spending money on it, I think I should just get rid of it.
I also noticed that the rear muffler is almost touching the heat shield. That could be the source of the drone in the cabin, but it does not touch.
I really don't want to be spending money here and there and end up in the same spot after throwing another couple of hundred bucks at it, but the OBX exhaust would cost me about $1000 with the current exchange rates (I'm in Canada) just for the kit. :( My test pipe is v-banded to the downpipe, so I guess I would have to get that re-welded at the shop, so it sound like I cannot avoid taking it there for an install, as I don't have a way to weld up a new one. :(

[eljay]

Another question/thought: would swapping for a 2.5" exhaust reduce the drone/loudness? Or specifically, if I were to replace the current 3" dp with a 2.5" one. Then I'd have 3" test pipe into 2.5" downpipe.
I'm not concerned about any 5hp loss as long as the turbo's health/longevity is not affected. Thanks.

[Fast4esT]

Have the welds at each pipe and muffler coupling checked. A slight leak in the weld to the muffler will be a considerable amount louder than no muffler at all.

[Fast4esT]

I wonder what Borla mufflers would be like on the avant? Anybody run them?

[redline380]

I wonder what Borla mufflers would be like on the avant? Anybody run them?

I have a b5 s4 borla muffler on my b5 1.8t. Even though I also have a glasspack midway, it is pretty loud.

[AudiA4_20T]

Look into Borla, old guy has it, have not heard him complain about drone. I have Almost the same setup as you and I do get a little drone around 1.8 - 2k after that it smooths out. I have no clue what your problem could be, maybe as mentioned above, check for exhaust leeks.

Borla w/ a test pipe on my stock K03 was one of the best systems I ever heard on a B6.

[Fast4esT]

finding my magnaflow a little raspy, not sure what mufflers they are though

[onceover]

APR/Billyboat Stealth Exhaust FTW

[old guy]

Borla w/ a test pipe on my stock K03 was one of the best systems I ever heard on a B6.

I have been extremely happy with my Borla. I installed it 10 years ago and it is still in great shape. I spend a lot of time on the Interstate so I'm not interested in anything that drones even a little.

The Borla is fairly quiet but has a nice growl when you get on it. Here's what it sounds like with a 034 HFC and TT 2.5" downpipe. Not the best recording but it will give you an idea. Sounds much better with headphones.

[Fast4esT]

Breaking the speed limit for the win old guy, I've read through a few of your posts on the Borla.

I'm debating on replacing my magnaflows, I have 3" running from turbo to the Y that splits into 2.5s I'm pretty sure. I'd rather just swap out mufflers than the whole system but also wondering if I should add resonators after the Y.
Been debating for 3 years, perhaps I need to experiment with it.
I'd keep my muffler and add resonators but OP says his setup is loud which makes me contemplate another muffler.

Also, does having the tips protrude out from the bumper change the sound or resonance at all? As opposed to being flush with bumper? Do 4" tips resonate more compared to say 3"?

[old guy]

That was done on a closed course under adult supervision ;-)

You would be amazed how much a thin walled stainless steel exhaust line "grows" when heated up. When cold my tips protrude a little over ½". When I make a spirited run the exhaust line lengthens to a little over 1" protrusion. I don't think the amount of protrusion makes much difference in the sound.

And I don't think the tip diameter really makes much of a difference either unless it is a resonated tip. Then it will change the exhaust note.

[MagnaFlow]

We would second the idea to check all the welds for leaks before anything. That being said, your exhaust seems to have a lot of "stuff" going on with it. Removing the stock cats will increase your chances of drone, so going back to a stock cat setup would be recommended. You can then swap your existing cat for a nice middle resonator like our 5x11x28" Y. Also the flex pipe and bullet-style resonators can be trashed-you don't need them. This should improve on the current setup and cut down on the drone. We'd be happy to help you with any application questions you may have, so please let us know!

[eljay]

That was done on a closed course under adult supervision ;-)

You would be amazed how much a thin walled stainless steel exhaust line "grows" when heated up. When cold my tips protrude a little over ½". When I make a spirited run the exhaust line lengthens to a little over 1" protrusion. I don't think the amount of protrusion makes much difference in the sound.

And I don't think the tip diameter really makes much of a difference either unless it is a resonated tip. Then it will change the exhaust note.

Thank you for that video! That does sound nice and drone-free would be amazing. So, that's a 3" HFC into a 2.5" dp and Borla exhaust all the way back?
Would connecting a 2.5" downpipe and 2.5" exhaust after that to that 3" test pipe I have be detrimental to my turbo's longevity/reliability? That 034 HFC would be nice, but since my SAI system is gone, there's probably no point in that, correct?

[eljay]

We would second the idea to check all the welds for leaks before anything. That being said, your exhaust seems to have a lot of "stuff" going on with it. Removing the stock cats will increase your chances of drone, so going back to a stock cat setup would be recommended. You can then swap your existing cat for a nice middle resonator like our 5x11x28" Y. Also the flex pipe and bullet-style resonators can be trashed-you don't need them. This should improve on the current setup and cut down on the drone. We'd be happy to help you with any application questions you may have, so please let us know!

Thank you for chiming in. Yes, lot of "stuff" going on there for sure. There used to be this center muffler in place of that cat:


But that muffler got a hole in it when it scraped on something being that low. I bought the car like that, so I'm not sure how the exhaust sounded with that muffler without a hole in it. Perhaps it was nice and quiet. Anyways, putting the cat in there wasn't the best of ideas, but I needed it for inspection at the time, so I gave the shop the OK to put one in and that's all they could get in at that time.

When the winter is over, I will do another seafoam test of the exhaust and watch carefully for leaks. V-bands are used throughout, so it's possible one of them is not tight and causing a slight leak. This also makes it tricky to bolt on another exhaust to that test pipe since it has a vband flange on it. But if I do buy another one, I'll make sure to use a shop with some good welds to weld on a vband flange for me to connect the test pipe with downpipe.
Seeing that I will need to replace the flex joint, perhaps I'll just get a whole new downpipe that does not hang as low as this one and connect it to a resonated Y-section and then to the existing rear sections. I just don't want to be experimenting anymore. It costs just as much as a proper bolt-on exhaust, which may just be the best solution for me. The whole exhaust is in a good shape, so may be it will be good for someone else who can get it properly set up.

Cheers.

[old guy]

Thank you for that video! That does sound nice and drone-free would be amazing. So, that's a 3" HFC into a 2.5" dp and Borla exhaust all the way back?
Would connecting a 2.5" downpipe and 2.5" exhaust after that to that 3" test pipe I have be detrimental to my turbo's longevity/reliability? That 034 HFC would be nice, but since my SAI system is gone, there's probably no point in that, correct?

That's correct. The Borla exhaust connects to the 2.5" downpipe. I chose to run the 3" 034 cat to reduce the smell as well as being able to pass emissions.

I don't think running a 3" test pipe to a 2.5" downpipe to the Borla exhaust would be any more restrictive that what you are running now since you are already running through a 2.5" Magnaflow cat.

[drjonez]

APR/Billyboat Stealth Exhaust FTW

Heck no. While it probably won't drone as bad as the OP's, it certainly isn't quiet or drone free....

OP- the "easiest" solution is a quarter wave resonator tuned to your car. Here's what a B7 guy did:

http://www.audizine.com/forum/showth...eing-installed

[CyberPMG]

APR/Billyboat Stealth Exhaust FTW

Agree it's a great sound, but the quality is total crap. They can't weld anything right. Have gone through 4 replacements over the past 10 years.

[CyberPMG]

I'm thinking I may want to finally give up on APR/Billy Boat and go with something else that is of better build quality but still is quiet in the cabin and has a pleasing low tone with a good growl when getting on it. Anyone want to sponsor me for long term testing? Guaranteed will get exposed to all weather conditions.

[onceover]

I traded my Magnaflow 16601 system for the APR one and haven't had any issues. It's a few years old and still holding together. I get very little drone on the highway with a test pipe and GT3076

[eljay]

That's correct. The Borla exhaust connects to the 2.5" downpipe. I chose to run the 3" 034 cat to reduce the smell as well as being able to pass emissions.

I don't think running a 3" test pipe to a 2.5" downpipe to the Borla exhaust would be any more restrictive that what you are running now since you are already running through a 2.5" Magnaflow cat.

Thanks!
Does SAI delete have any detrimental effect on the cat itself? I understand that its role is key on cold starts before the cat heats up.
I ask because I still have both O2 sensors on the test pipe (obviously they are not doing much without a cat in the middle), so if I were to get a 3" HFC would the lack of SAI and O2 sensor-driven mixture adjustment ruin it over time?
Like you, I like a fume-free exhaust.

[eljay]

Does anyone have the OBX catback exhaust with a similar turbo and test pipe? What is the loudness/drone with that setup?

[old guy]

Thanks!
Does SAI delete have any detrimental effect on the cat itself? I understand that its role is key on cold starts before the cat heats up.
I ask because I still have both O2 sensors on the test pipe (obviously they are not doing much without a cat in the middle), so if I were to get a 3" HFC would the lack of SAI and O2 sensor-driven mixture adjustment ruin it over time?
Like you, I like a fume-free exhaust.

Replacing the 3” test pipe with a 034 HFC should help reduce the drone a little.

Not having the SAI in place may be extremely detrimental to the cat, depending upon how your tuner addressed removing the SAI.

If the tune simply writes out the CEL and readiness code but leaves the cam advance, fast idle and timing retard in place you will be pumping a lot of unburned fuel directly into the cat. The SAI pump adds a lot of air into the exhaust stream to complete the combustion and quickly heat the cat. If the extra air isn’t present the cat life will be greatly reduced.

If the tune completely writes out all of the SAI functions you should be OK.