Turbo Resonance Dampener Removal

While at the Texas TDI Club GTG yesterday, TDIinTexas lent me a hand a couple of times and we managed to pull my "turbo muffler". For those that don't know about this, VW decided to cut down on noise by putting a muffler on the compression housing outlet pipe of the turbo on the 2.0 CR TDI's. The result is that the turbo is exhaling through a 1 1/8" straw on its way to the engine.


IMG_0278 by Toe_Ball, on Flickr

This is the dampener housing after it's been gutted. At the top of the picture by the Dremel you can see one of the baffles (or what's left of it). The diameter of the whole dampener was the same as the ID of the baffle chunk. Definite flow improvement.

Well anyway, we managed to pull this out, and then I opened it up using a Dremel, a hole saw and a lot of time, I hollowed it out, and smoothed it as best I could, not perfect, but good enough for the time being. TDIinTexas has drawn up the flange and thinks he can make an aluminum replacement, which will be nice as it's bound to flow better than my Dremeled out phenolic plastic one.

On my 5 hour drive home, I noticed a few things of interest. On the freeway, cruising, the engine sounds about the same. When accelerating, above 2500 RPMS under high load, the engine makes a more pronounced growling sound. Above 3000 RPMS under medium load or higher, a distinct hiss is audible, no whistle. There is definitely less turbo lag, quite a bit less. I seem to be getting better millage.

This last one, I'll have to monitor to be sure, it's only based on instant mileage. My average driving up to the GTG was 37.5 MPG, my average on the return was 39.7 MPG. Driving conditions were significantly different. I hit traffic on my way back, I tanked up so fuel could be better quality, I was technically driving down hill on the way back as well. I also took a different route, but I don't think that was beneficial. Anyway, too many variables for those numbers to be absolute, but I do think that the engine breathing easier did improve mileage.

Very interesting! There aren't many threads I subscribe to, this one is an exception! Thanks for sharing this! How hard is it to remove this piece?

Thanks for the write up. Diesels love more air so it will only make sense that in the overall scheme of things, you should see better MPG's and maybe even less frequent regens as well. Keep us posted on this!

Is this turbo muffler down at the turbo exit before the intercooler or up top on the intake manifold?

I recall reading another thread about there being a turbo muffler at the intake manifold. If what you modded is down at the turbo exit, there might be a second muffler to take out at the IM.

I was wondering what effect(s) there might be on the DPF with the muffler removed. With the muffler in place and pushing air thru the "straw" it creates, the turbo has to spool harder to get air to the engine. EGTs may be higher with the muffler in place. I was thinking removing the muffler may lower EGTs some and that is a good thing in general but I wonder if EGTs will remain high enough for passive regen to still occur in nomal driving. If the engine breathes better due to the mufflerectomy it may not matter due to less soot being produced in the first place.

Anyhow it's a cool mod.

Good luck.

ToeBall said:

TDIinTexas has drawn up the flange and thinks he can make an aluminum replacement....

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I'd definitely consider an aluminum bolt-on replacement. Please keep us posted.

I knew that there was a turbo resonance dampener, but I had no idea how restrictive it was. This is the first thread I have ever subscribed to. I am very interested is the aluminum replacement. I would also love to hear how difficult (or easy) it is to remove and replace this piece (some pictures and a DIY post would be really nice). Keep the info coming, please.

Have Fun!

Don

I would definitely be interested in this. Anyone doing this please take some pictures...

Can anyone think of a reason removing the dampener would be bad for the engine?

UberVW_TDI said:

I would definitely be interested in this. Anyone doing this please take some pictures...

Can anyone think of a reason removing the dampener would be bad for the engine?

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Only if you did the mod wrong and left debris inside somewhere and it was blown into the engine. Diesel engines can never be run too lean so there is no risk there. The more airflow to a diesel, the better... And the easier it can get there, the better, too.

Very interesting thread, thank you for doing this and posting.

For general information and not directed at any specific member, here is the text about the flow damper from the VW 2.0L CR self-study:

"A flow damper is located behind the outlet of the turbocharger in the charge air section. It has the task of reducing disagreeable noise from the turbocharger, such as whistling.

Design and Function

During full-load acceleration the turbocharger must build up boost pressure very quickly. The turbine and compressor wheel are accelerated quickly and the turbocharger approaches its pump limit. This can lead to burbling in the air flow, which causes disturbing noise that radiates into the charge air section.

The charge air causes the air in the resonance sections of the flow damper to vibrate. The vibration has approximately the same frequency as the noise in the charge air. Disturbing noise is minimized by superimposition of the charge air sound waves with the vibration of the air in the resonance sections of the flow damper."

I was just looking at the self-study too. I'd love for someone to do this and take before and after pics. Looking at the diagram in the self-study, it looks like the baffles are the same diameter as the outlet. Looking at the piece in the picture here, i'm not sure that's the case. Don't suppose there's a before shot?

Honeydew said:

During full-load acceleration the turbocharger must build up boost pressure very quickly. The turbine and compressor wheel are accelerated quickly and the turbocharger approaches its pump limit. This can lead to burbling in the air flow, which causes disturbing noise that radiates into the charge air section.
The charge air causes the air in the resonance sections of the flow damper to vibrate. The vibration has approximately the same frequency as the noise in the charge air. Disturbing noise is minimized by superimposition of the charge air sound waves with the vibration of the air in the resonance sections of the flow damper."

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Well from this I take that it is just a noise suppressor and there should be no ill affects in deleting it. Now if it was there to keep the turbo from surging, well then that is a horse of a different color. I have seen the ill affects of surging and really dont want to mess with that again. It eats center sections.

JSWTDI09 said:

I knew that there was a turbo resonance dampener, but I had no idea how restrictive it was. This is the first thread I have ever subscribed to. I am very interested is the aluminum replacement. I would also love to hear how difficult (or easy) it is to remove and replace this piece (some pictures and a DIY post would be really nice). Keep the info coming, please.

Have Fun!

Don

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Sorry about that. Kinda got my hads dirty pulling it and didn't stop until the food was ready...

The pull's not that hard. Tranny needs to be in reverse with the 6MT to get the damper out. Other than that it's pull the engine cover, pull the air box, the main tube and it's two bolts holding the damper onto the aluminum turbo housing. Undo the hose clamp holding the rubber coupler to the pipe running to the intercooler, and pull everything out. Then remove the other hose clamp and start pulling the muffler apart. Reinstall the o-ring and reverse the install to put the car together.

The only real problem we had was that my hands are too big to get in there and undo the bolts holding the muffler to the turbo and slip the coupler back on. TDIinTexas did that for me. Thanks! Actually took about 4-5 hours for everything including BBQ.

mattymx said:

Only if you did the mod wrong and left debris inside somewhere and it was blown into the engine. Diesel engines can never be run too lean so there is no risk there. The more airflow to a diesel, the better... And the easier it can get there, the better, too.

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Easy to do. With the Dremel you accumulate a lot of turbo muffler powder by the time you're done gutting it.

geektoad said:

I was just looking at the self-study too. I'd love for someone to do this and take before and after pics. Looking at the diagram in the self-study, it looks like the baffles are the same diameter as the outlet. Looking at the piece in the picture here, i'm not sure that's the case. Don't suppose there's a before shot?

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Sorry, dirty hands, didn't want to handle my phone if I could avoid it, no photos... next time maybe.

mattymx said:

Well from this I take that it is just a noise suppressor and there should be no ill affects in deleting it. Now if it was there to keep the turbo from surging, well then that is a horse of a different color. I have seen the ill affects of surging and really dont want to mess with that again. It eats center sections.

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Don't know. The sound change isn't night and day drastic, but it's there, and pleasant. The only huge difference is less lag, so it's possible. If someone in the Houston area has VAGCom and wants to go for a ride and do some logging, I'd love to see what this puppy's actually doing.

Less lag is a good thing. That should help keep the DPF a little cleaner.

Big thumbs up Toe. Does it whistle with the stock airbox ?

I guess mine is coming out soon.

sounds easier now with the last explanation you gave. i may give this a shot over the weekend

Please keep us appraised of changes in your mileage. As hot as the mileage war with hybrids is, and considering how expensive and complex the TDI engine is, it's surprising that VW would add so much restriction to muffle a little hiss.

Here is a video I made of the neuspeed intake with the muffler. I will make another one as soon as I take out the muffler.

http://www.youtube.com/watch?v=myRifdIaJyA (720P sounds best)

Slo.Mo.Shun said:

Big thumbs up Toe. Does it whistle with the stock airbox ?

I guess mine is coming out soon.

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No it doesn't really whistle, it kinda hisses and it's not loud or obnoxious, just sort of there when you get on it. I'll check out the video when I get home. YouTube is blocked at work.

can you get a part number from this?

And wasn't there another post like this but it was for the exhaust side of the turbo or another noise suppressor??

KraftwerkB6 said:

can you get a part number from this?

And wasn't there another post like this but it was for the exhaust side of the turbo or another noise suppressor??

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I could have while I had it off. There's a VAG part number on the outside of the body, but I didn't think to note it down. Just wait for TDIinTexas to make the aluminum version if you don't want to modify the original, it'll probably flow better anyway.

As for the exhaust side, on mine at least, the DPF mounts directly to the turbo and acts as the 90 degree bend for the exhaust system. It goes to the flex joint, followed by a down tube, the nitrogen cat, a flapper valve, the sulfur cat, and then pipe to muffler and tips. I don't have a muffler and everything behind the sulfur cat is 3" pipe. Still very quiet.

From what I am getting here, the turbo resonance dampener is implemented to control unwanted noise from the turbo... if that's the only purpose it serves and thus makes the engine less efficient, why would the VW engineers do this? Has to be more to it, no?

Well i looked at one this morning while i was working on it. If what you posted was correct and i was looking into the right spot. It hooks up to the intlet side of the turbo and the other side hooks up to the intake tube. 2 bolts and looks pretty easy to get to it.

I might see if parts has one i can look at before i would take mine off and see a better diagram of one for refrence. IF i do take mine off today or tomorrow i will take pics so others can see.

How do you know the dampener is making the engine less efficeint? to me it sounds like it cancles standing waves in the charged air side. Which in my mind removing it thus causing these standing waves would make it less efficent, but only time will tell.

The idea of "cut everything out and straight pipe it" always isn't the best.

bruce846 said:

From what I am getting here, the turbo resonance dampener is implemented to control unwanted noise from the turbo... if that's the only purpose it serves and thus makes the engine less efficient, why would the VW engineers do this? Has to be more to it, no?

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It is pretty obvious that VW went to great lengths to disguise the "dieselness" in these new CR engines. They wanted it to be as quiet as possible. My guess is that this is the reason.

KraftwerkB6 said:

Well i looked at one this morning while i was working on it. If what you posted was correct and i was looking into the right spot. It hooks up to the intlet side of the turbo and the other side hooks up to the intake tube. 2 bolts and looks pretty easy to get to it.

I might see if parts has one i can look at before i would take mine off and see a better diagram of one for reference. IF i do take mine off today or tomorrow i will take pics so others can see.

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We would all be very grateful to see your pics.

Have Fun!

Don

KraftwerkB6 said:

Well i looked at one this morning while i was working on it. If what you posted was correct and i was looking into the right spot. It hooks up to the intlet side of the turbo and the other side hooks up to the intake tube. 2 bolts and looks pretty easy to get to it.

I might see if parts has one i can look at before i would take mine off and see a better diagram of one for refrence. IF i do take mine off today or tomorrow i will take pics so others can see.

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No it connects to the output of the compressor housing, below and behind the inlet. The inlet tube needs to be removed to get access. Maybe I'm misunderstanding your post? Pictures would allow me to be positive, but the 2 bolts to the turbo leads me to believe it is the correct part. I didn't notice anything else on there that mounts with 2 bolts. Well, the PCV mounts to the turbo right before the inlet but it mounts with 1 bolt downwards and seems to be glued on or something. I couldn't figure out a safe way to remove it for access anyway.

740GLE said:

How do you know the dampener is making the engine less efficeint? to me it sounds like it cancles standing waves in the charged air side. Which in my mind removing it thus causing these standing waves would make it less efficent, but only time will tell.

The idea of "cut everything out and straight pipe it" always isn't the best.

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It's not the function that reduces the efficiency, it's the reduction of diameter from 2 1/4" down to a bit over 1" and then back up to 2 1/4". It's a muffler, yes, but it's also an orifice tube for the charge air side. Basically it acts as a restrictor plate.

I would think that restriction on the exhaust side of the turbo would cause it to spool faster, not slower.

^Totally agree with this.

IndigoBlueWagon said:

I would think that restriction on the exhaust side of the turbo would cause it to spool faster, not slower.

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I'm curious, please explain.

ToeBall said:

I'm curious, please explain.

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When you block the airflow of a centrifugal fan (which is what the compressor side of the turbocharger is), the RPM's will increase. This is easily demonstrated for instance with an electric air pump for inflatable beds or a vacuum cleaner, turn it on, the block the intake (or exhaust) with your hand and you can hear the RPM's increase.

This is due to the fact the the pump is actually doing less work as the air flow is restricted. Placing an amp-meter on the circuit will also show a drop in amperage (motor is doing less work). It is counter-intuitive, but ask any Physics student or HVAC repairmen, they will be familiar with it.

A more lengthy explanation:
http://hvacrfundamentals.blogspot.com/2009/08/understanding-centrifugal-fan-motor.html

The low pressure in the throat of a venturi can be explained by Bernoulli's principle; in the narrow throat, the air is moving at its fastest speed and therefore it is at its lowest pressure.