# Get rid of the muffler (Back Box) on my 2L TFSI TT



## Hadaak (Dec 25, 2008)

I've read that some engines need some back pressure... just in case you have any info.... 
TT sounds good without the muffler, like an RS :lol:


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## Hadaak (Dec 25, 2008)

mmmmm... no opinions... means i'm fine to go :mrgreen:


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## Toshiba (Jul 8, 2004)

I'm sure it will work as good as the last exhaust mod :wink:


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## BLinky (Jul 3, 2009)

why not just get rid of the pipes and remove the entire manifold, it'll sound awesome then.


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## Hadaak (Dec 25, 2008)

plus TT will lose some 20 kg :wink: 
wonder what effect such loss will have on the overall stability if ever the muffler is part of the stability thing like the spoiler


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## Hadaak (Dec 25, 2008)

Toshiba said:


> I'm sure it will work as good as the last exhaust mod :wink:


mmmmmmm....not sure how to interpret this :lol:


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## Hadaak (Dec 25, 2008)

BLinky said:


> why not just get rid of the pipes and remove the entire manifold, it'll sound awesome then.


are you serious ?


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## talk-torque (Apr 30, 2008)

Are you?


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## Hadaak (Dec 25, 2008)

of course I'm serious. I did rip that muffler to pieces to get what I wanted. now when I took the muffler off I see this possibility of going further and getting some sound on and some weight off. why wouldn't I be serious? I always do what I say :wink: even if the TT goes to pieces  
I don't think i'm the first one to delete a muffler !


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## BLinky (Jul 3, 2009)

Hadaak said:


> BLinky said:
> 
> 
> > why not just get rid of the pipes and remove the entire manifold, it'll sound awesome then.
> ...


yeah why not? did it to a prius and it was the loudest thing in the world other than the auto union racer, no seriously you'd be suprised how low cars go without a exhaust manifold.


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## Hadaak (Dec 25, 2008)

back on track 

Hadaak CatBack is alomost ready 

I haven't installed it yet as we couldn't finish welding yesterday. so will be installing it in two or three days.
I'll make a video and let you know how it sound.

Enjoy the pics


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## McKenzie (Dec 25, 2008)

Excellent work, looking really good. what inch" pipe did you go for?


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## Hadaak (Dec 25, 2008)

I had to go for 60 mm to be able to connect to the original system behind the middle muffler.
Audi use 63-65 mm from behind the middle muffler.

the flow should be ok though.
I have no idea how it will sound :lol:


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## McKenzie (Dec 25, 2008)

does look good, I think 70mm to 76mm would have a decent amount more flow but not sure it would make much better performance readings. Sound wise the sound might be a bit of a higher note due to the smaller bore size. Should be interesting, Keep us posted.


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## bozzy96 (May 26, 2009)

Why the faceless man, Or is that where Elvis works, Thank you very much !!! :lol: :lol: :lol:


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## wallstreet (Oct 19, 2009)

Did you just decrease size? Not the best idea. A mandrel bend is far better to reduce turbulance inside the pipes that also makes a difference. Well done on trying a DIY!

You should google constant flow of velocity and back pressure to get it right.


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## Hadaak (Dec 25, 2008)

size is decreased by 3 mm. Audi tube is not even stainless steel  
it is just plain steel. the back box is stainless steel though.
My friend doesn't have Mandrel tools and I couldn't find a an easy place to Mandrel it  
The flow should be ok as all the juncture where welding is done are almost cut clean. It took us a whole day to do all the measuring and the assembling !


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## Hadaak (Dec 25, 2008)

interesting post post I read before doing the muffler delete mod:

http://www.uucmotorwerks.com/html_product/sue462/backpressuretorquemyth.htm

*Some say that "an engine needs backpressure to work correctly." Is this true?

No. It would be more correct to say, "a perfectly stock engine that cannot adjust its fuel delivery needs backpressure to work correctly." This idea is a myth. As with all myths, however, there is a hint of fact with this one. Particularly, some people equate backpressure with torque, and others fear that too little backpressure will lead to valve burning*

don't know how Audi deal with this !
Hope I won't be burning the valves with this mod :-|


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## BlackRS (Mar 9, 2010)

Am I right in thinking a turbo engine has all the back pressure it requires from the restriction caused by the turbine, and you can do what you want downstream?


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## Hadaak (Dec 25, 2008)

you're certainly right as when I ripped open the OEM muffler I found that there is a direct pipe going through the big box till the endpipes. so the gazes don't go through any chambers or whatsoever. the pipe is enveloped in glass fibre for noise muffling and there is a small chambre on the right side (passenger side) with a pipe of about a 20mm diameter going from this chamber into the straignt pipe. I think it was there to make a specefic sound note or something. I blow compresed air though the exhaust and there was no air ever entering this chamber.

since backpressure is all the restriction that the flow of gaz gets travelling through the pipes till the outlet I'm reproducing the OEM system probably with a minor restriction (60mm pipe instead of 63-65). But my system is shorter and deletes the last curve inside the OEM muffler. So end of the day I might have the same flow (if not better) but more noise. just hope more noise won't be horrible noise :mrgreen:

The muffler on the pics is standard TT one modified to have Quad Tips


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## [email protected] (Jan 14, 2010)

Interesting work thread here. I would have been curious to see a before and after dyno, I understand the math you are using. Smaller diameter with less restrictions... Curious to say the least! I am digging the craftsmanship regardless.


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## Hadaak (Dec 25, 2008)

the diameter difference is pretty small. It was easier to go with 60 to connect to the OEM system behind the middle muffler.
too late for a before-after dyno now as I already ripped and modded the original back-box but I might get a fellow TT owner to lend me his backbox for a dyno run  or I could just do a dyno and compare it with a standard exhaust equippe TT 

And My TT is losing some 25 kg :lol: getting ready for summer :mrgreen: 
so there should be some power gain in the final combination :mrgreen:


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## Hadaak (Dec 25, 2008)

Good news and some bad news too !

the exhaust is installed. sound is good but there is too much resonance inside the car.
and since mine is Stronic the sound following a gear change in D mode (changing like at 2000 RPM) is loud and resonates too much. starting from cold this morning sounded like a Jumbo jet  . overall I can give a note of 7/10. i think that adding a small muffler at the back will make a 10/10  . Someone said It sounded like a big bike :wink:

Will upload pics and a video with sound.

anybody report the cabin sound of the milltek or atermarket catbacks, with Stronic if possible?


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## Hadaak (Dec 25, 2008)

first video :


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## Hadaak (Dec 25, 2008)

Second video:


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## Hadaak (Dec 25, 2008)




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## steve1988 (Jan 3, 2010)

thats sounds nice... not sure if my street would like me going to work on a morning thow 

think i will stick to removing cat and having a small box on back to keep noise a bit more low :?

you happy with the results??


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## Hadaak (Dec 25, 2008)

almost happy  
There is more noise inside the car than outside now 

a small muffler in the back would be ok. I'll see what I can do to reduce the internal noise or resonance.


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## steve1988 (Jan 3, 2010)

ok good luck 

i shall be starting mine over the next few week so will get a thread going with some pics and vids without the cat


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## [email protected] (Jan 14, 2010)

Ok, this is 100% exactly what you need. Not sure if you can get them over there or not but we use these like candy here for exactly what you've created. I'll let the pic and the link do the talking!

http://www.summitracing.com/search/?key ... bomb&dds=1









They are called cherry bombs and they are inline glass pack mufflers. High flow but manages removes that pingy motorcycle sound without hardly any loss of power.


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## McKenzie (Dec 25, 2008)

Sounds pretty nice, I would be interested to see how loud the whole system would be without the restrictive factory downpipe and cat and replaced with just a downpipe and sports cat.


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## Hadaak (Dec 25, 2008)

[email protected] said:


> Ok, this is 100% exactly what you need. Not sure if you can get them over there or not but we use these like candy here for exactly what you've created. I'll let the pic and the link do the talking!
> 
> http://www.summitracing.com/search/?key ... bomb&dds=1
> 
> ...


thanks Chris. I was thinking of something like that  
But I'm starting to like the sound :mrgreen: 
I met a fellow TT owner in town and he wanted to have the same sound :mrgreen: 
So I might be starting a new business here  Milltek have serious worries here


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## [email protected] (Jan 14, 2010)

We'll get tickets for being that loud [smiley=bigcry.gif]


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## Toshiba (Jul 8, 2004)

deleted


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## Hadaak (Dec 25, 2008)

McKenzie said:


> Sounds pretty nice, I would be interested to see how loud the whole system would be without the restrictive factory downpipe and cat and replaced with just a downpipe and sports cat.


Would run louder if you don't add some noise tuning at the back. 
I like the note now for normal driving but when I hit the pedal it does sound loud and resonates inside the car. 
I I go Stronic the whole car shakes like crazy 
The poor car will fall to pieces in no time with all the vibations it goes through :mrgreen: but I feel the car now  
will keep this system for the moment and maybe add a small muffler, like chris suggested, later.


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## Hadaak (Dec 25, 2008)

Hadaak said:


> McKenzie said:
> 
> 
> > Sounds pretty nice, I would be interested to see how loud the whole system would be without the restrictive factory downpipe and cat and replaced with just a downpipe and sports cat.
> ...


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## McKenzie (Dec 25, 2008)

I think since you haven't done any downpipe/cat work its probably bearable but in future you might go for a little adjustment.


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## alexf (Nov 1, 2009)

Great piece of work. From where did you get the bends?


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## Hadaak (Dec 25, 2008)

Thanks.
My friend who owns the metal workshop ordered the tube and the elbows for me. around 70 € in all + the endpipes which I got from germany. around 75€ including delivery. It took 3 m of tube (60mm diameter) and 8 elbows. 
The important thing is all the items should be real stainless steel (Anti-magnetic) 304L standard so they don't rust.
The welding was done using stainless steel too.


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## twocati (Dec 6, 2009)

Hadaak - Thanks for sharing - I'm really impressed with the quaility of work and attention to detail on this project !!


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## Hadaak (Dec 25, 2008)

Thanks :wink:


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## Hadaak (Dec 25, 2008)

[email protected] said:


> Ok, this is 100% exactly what you need. Not sure if you can get them over there or not but we use these like candy here for exactly what you've created. I'll let the pic and the link do the talking!
> 
> http://www.summitracing.com/search/?key ... bomb&dds=1
> 
> ...


Hi Chris,

I read this about the Cherry Bombs : Disturbing the Peace Since 1968 !!! 
Are you sure this is going to reduce the noise or resonance?


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## [email protected] (Jan 14, 2010)

It won't make it something that you can have a baby take a nap in, but it will make it just quite enough to pass our noise restrictions for db levels and they do a great job of masking resonance. They are very popular on small displacement turbo charged cars here.


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## Hadaak (Dec 25, 2008)

ok.
Now any idea how to install them in my system. I mean do you think I need one in the middle or two at the back, one on each side just before the tips?

I might go for only one before the Y junction if they are not very thick.


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## McKenzie (Dec 25, 2008)

Just one somewhere along a straight piece of piping would be the best.


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## [email protected] (Jan 14, 2010)

McKenzie said:


> Just one somewhere along a straight piece of piping would be the best.


Indeed.


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## McKenzie (Dec 25, 2008)

[email protected] said:


> McKenzie said:
> 
> 
> > Just one somewhere along a straight piece of piping would be the best.
> ...


 :lol: That did sound slightly stupidly put but what I meant was you will only need one and the positioning doesn't matter too much.


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## [email protected] (Jan 14, 2010)

McKenzie said:


> [email protected] said:
> 
> 
> > McKenzie said:
> ...


No I was serious! Just one in line would do the trick.


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## Hadaak (Dec 25, 2008)

I found an interesting thing here. It's called quaterwave resonator. I now understand the function of the right side tube in the original audi backbox. Well I knew it had to do with noise muffling. look at this exhaust design. The small tube indicated by the arrow is a quarterwave resonator that is there to deal with some specific frequencies. it is just a tube with a specific diameter and length.










Audi BackBox:










info from my friend Google : (http://blog.autospeed.com/2003/11/30/th ... o-intakes/):

_Quarter wavelength resonators are characterised by having a constant diameter. Their resonant frequencies are determined by their length - for example, a quarter-wavelength resonator with a centre frequency of 67Hz (the firing frequency of a four cylinder engine at 2000 rpm) is 1250mm long._

it is apparently tricky to calculate but I might try to make one for fun


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## sTTranger (Oct 21, 2008)

WOW  

SO could you have a straight pipe with the one in the pic welded on to stop the resonating???


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## Hadaak (Dec 25, 2008)

might be worth a try :wink:


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## Hadaak (Dec 25, 2008)

I did this mod :










I placed it just before the Y junction. I took pics but forgot to put a Memory stick card in the camera :twisted: 
will take some pics later.

The exhaust note has changed. less resonnance (there is still some though) but more vibration when I open it wide. note is alose good in higher revs. the mod needs tweaking to calculate the lenght of the tube. we put a 17 cm tube. I will probalbly make an adjustable (sliding) one to get the right length before welding it once and for all. 
I think that adding a small muffler before the T resonnator will finish the mod. if not I'll go for a Milltek :mrgreen:


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## McKenzie (Dec 25, 2008)

Hadaak said:


> I did this mod :
> 
> 
> 
> ...


Haha you cant for a Milltek after all of this! that would be such a waste. Best thing you can do is just stick a cherrybomb/small silencer along part of the section. Top marks for the effort though!


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## Hadaak (Dec 25, 2008)

Thanks  
will try the cherry bomb. if I get it right I'll start manufacturing :mrgreen:


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## Hadaak (Dec 25, 2008)

Small update here. Did this a few weeks ago and haven't had the time to update the thread.
The sound is good ans the resonance is almost gone at low speeds. The sound is still loud at high speeds :lol: 
Enjoy


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## TT-driver (Sep 14, 2010)

Top marks for effort and apparently results. Would place something to close that gap though that you've created by removing the muffler. Your rear bumper is now acting as a parachute and causing additional turbulence. Perhaps a decent diffuser would be nice.


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## Fissues (Aug 11, 2008)

Look great! Let's hear it.


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## Hadaak (Dec 25, 2008)

TT-driver said:


> Top marks for effort and apparently results. Would place something to close that gap though that you've created by removing the muffler. Your rear bumper is now acting as a parachute and causing additional turbulence. Perhaps a decent diffuser would be nice.


thanks. Yeah I thought of that detail but since I'm still working on the project I might add something at the end :wink:


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## Hadaak (Dec 25, 2008)

Fissues said:


> Look great! Let's hear it.


Thanks. will upload a vid asap :wink:


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## TTfreak330 (Feb 2, 2012)

Isthis exhaust still alive?
I have a milltek downpie with the cat removede en all silencerces removed only a milltek on the back. 
Sounds very good! But i was thinking too to remove the milltek silencer but then i would have nothing of silencer and it would maybe be to much.haha.

Gr


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## Hadaak (Dec 25, 2008)

still alive and roaring :lol:


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## TTfreak330 (Feb 2, 2012)

Do you maybe have a driving video? Do you still have the cat and middle silencers? I love your project! Respect!


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## TT-REX (Jun 3, 2011)

did the same whit 2 small reasonator , sounds perfectly powerful , i love it


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## TTfreak330 (Feb 2, 2012)

Do you maybe have a movie of rhe sound driving ect
You still have the cat anf mid silencer?
Looks perfect man!

Gr


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## TT-REX (Jun 3, 2011)

TTfreak330 said:


> Do you maybe have a movie of rhe sound driving ect
> You still have the cat anf mid silencer?
> Looks perfect man!


yes i still have the cat and mid silencer, just removed the big box , call it a y-pipe
nah i dont have any movie , ill try to take one tonight when i leave


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## TTfreak330 (Feb 2, 2012)

Thx! I'm curious about it!

Gr


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## Krpano (Dec 25, 2011)

i am curious too.


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## Hadaak (Dec 25, 2008)

TT-REX said:


> did the same whit 2 small reasonator , sounds perfectly powerful , i love it


You owe some copyright there, mate 

How does it sound in the cabin at 130 km/h and higher. I planned to add two resonators on the Y but went for a single one before the Y. It sounds good but there still is some resonance when cruising at 130km/h.

I'm thinking of changing the quad tips for dual RS style tips:


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## Hadaak (Dec 25, 2008)

TTfreak330 said:


> Do you maybe have a driving video? Do you still have the cat and middle silencers? I love your project! Respect!


Thanks mate :wink: 
I don't have any driving vids. And I still have the CAT and middle silencer. here is what changed:

Before:










After:










side by side:










And with the quaterwave resonator and the small resonator added:


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## Hadaak (Dec 25, 2008)

TT-REX said:


> did the same whit 2 small reasonator , sounds perfectly powerful , i love it


Yo TT-REX,

where did you get the two resonators? are they stainless inside out?


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## TT-REX (Jun 3, 2011)

^^ dont know how to explain but it sounds normal to me at 130km in the cabin, the two resonator, i got it from a muffler shop down here in montreal canada and yes there stainless in/out


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## TTfreak330 (Feb 2, 2012)

i wish i could here the sound while driving. what would it be if everything would be removed. cat and everything.

gr


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## Hadaak (Dec 25, 2008)

with this only:










it was LOUD especially above 110 km.

with one or two resonators it is still loud but cool 

if you can make one like I or TTREX did then do it and if not happy you can always go back to OEM :mrgreen:


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## TT-REX (Jun 3, 2011)

trust me u wont regret it if u do it like mine , i remember before when the car was sooo boringgg :lol:


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## Hadaak (Dec 25, 2008)

TT-REX said:


> trust me u wont regret it if u do it like mine , i remember before when the car was sooo boringgg :lol:


and this exhaust thing will kreep on you so you are always looking for that moment when you would floor it and smile  
Well not that V8 smile though


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