S3 8L Custom Exhaust Flow

[ShaunS3]

Hi guys,

I have on my S3 the following:

XS/Pipewerx 3'' DP
XS/Pipewerx 200 cell sports cat
Milltek Resonated cat back

Long story short, the sports cat reduces down from 3'' to between 2'' and 2.5'' iirc and sleeves into the Milltek system but for one reason or another the sleeving is incorrect and exhaust gases are blowing past, thus creating a whistle when throttle is applied.

My plan is to modify the sports cat (cut back to the 3'' bore) and tig weld a 5ft straight stainless pipe all the way through to the rear silencer, thus removing the resonator box and most of the exhaust bends creating a 'straight through' centre section.

My question is that if I am removing the exhaust bends, resonator and reducer within the sports cat (restriction) would i lose back pressure and ultimately lose power?

I'm unsure as to why the sports cat reduces right down from 3'' but i presume this is so it fits the standard OEM cat back system and doesn't accomodate the Milltek.

Can anyone shed any light on this?

Thanks in advance.

Shaun.

 

[Reesy]

Hi guys,

I have on my S3 the following:

XS/Pipewerx 3'' DP
XS/Pipewerx 200 cell sports cat
Milltek Resonated cat back

Long story short, the sports cat reduces down from 3'' to between 2'' and 2.5'' iirc and sleeves into the Milltek system but for one reason or another the sleeving is incorrect and exhaust gases are blowing past, thus creating a whistle when throttle is applied.

My plan is to modify the sports cat (cut back to the 3'' bore) and tig weld a 5ft straight stainless pipe all the way through to the rear silencer, thus removing the resonator box and most of the exhaust bends creating a 'straight through' centre section.

My question is that if I am removing the exhaust bends, resonator and reducer within the sports cat (restriction) would i lose back pressure and ultimately lose power?

I'm unsure as to why the sports cat reduces right down from 3'' but i presume this is so it fits the standard OEM cat back system and doesn't accomodate the Milltek.

Can anyone shed any light on this?

Thanks in advance.

Shaun.

Have a look in my thread at the last page or 2. I have just done the same thing and gone 3" straight through to the backbox..

The reducer will be for fitting to a stock system.

 

[ShaunS3]

Cheers Reesy.

I thought I had better ask before I proceeded as I've heard that removing bends etc can reduce power by creating a low velocity exhaust flow and/or too big of an exhaust bore.

The Milltek catback is 2.75'' so i'm going to be sticking with the 2.75'' in the straight pipe and using a couple of the angle bends of the Milltek to reduce the number of welds....might aswell put the Milltek centre section to good use if i'm going to be chopping it up.

 

[Lewis583]

It's only really NA cars that can lose performance by not having some back pressure.

With FI the least amount of restrictions (silencers/tightbends etc) downstream of the turbo the better, noise levels permitting ofc lol.

You will be fine fella and don't forget to put some pics up after you are done

 

[ShaunS3]

It's only really NA cars that can lose performance by not having some back pressure.

With FI the least amount of restrictions (silencers/tightbends etc) downstream of the turbo the better, noise levels permitting ofc lol.

You will be fine fella and don't forget to put some pics up after you are done

Just what i wanted to hear

 

[jezzy]

Time for a new manifold????????????????????????

 

[ShaunS3]

Time for a new manifold????????????????????????

No. I'm not chasing big power figures, just improving the poor fitment and gaining a better flow in the process.

 

[James TQ]

It's only really NA cars that can lose performance by not having some back pressure.

silly question, what are NA cars, iv seen alot on n/a cams in S3's?

 

[Reesy]

It's only really NA cars that can lose performance by not having some back pressure.

silly question, what are NA cars, iv seen alot on n/a cams in S3's?

Naturally Aspirated.

 

[ShaunS3]

Naturally Aspirated.

AKA - Non turbocharged / Non Supercharged

 

[RobinJI]

Just going to back up Lewis on this one, as he says, the less restriction the better with turbo cars. Besides the turbos presence in the exhaust and the positive intake pressure killing the idea of using the NA tuning devices like pulse tuning, the turbine wheel will operate most effectively with the least amount of pressure on the down-pipe side, giving the biggest possible pressure drop through it.

 

[ShaunS3]

Will I see more of a raspy note from this modification?

My understanding is that the rasps are caused by the gases hitting the bends within the exhaust system but I've heard people saying it will be more raspy.

 

[<tuffty/>]

You won't be able to run a straight pipe from the DP to the back box as the rear diff/haldex is in the way... bends in pipes do slow down air speed but on a 3" system at your power levels it is largely irrelevant...

The standard system is fairly bend free up to the back box.... here is my 3" system next to the OEM system

I changed this later as it was too loud on the poxy little back box...

...although I did try a full on straight through system for fun ;P

Don't get too hung up on it... Miltek systems are 2.75" OD IIRC and 3" is plenty for 500+ hp

<tuffty/>

 

[superkarl]

Shaun i have the same issues, milteks idea of 2.5 inch is alot different to relentless idea, or t'other way round, obv the americans are wrong. Anyway yeh i have a blow i cant get rid of no matter how tight i do the sleeve.



Consider this, cut the decat/cat pipe where it is 2.75 inch, i.e where it reduces, and get a straight piece of 2.75 welded on, and the v-band both the downpipe and the miltek. Hey presto, 3inch-2.75inch all the way that will never ever leak or blow. V-band ftw

 

[ShaunS3]

Shaun i have the same issues, milteks idea of 2.5 inch is alot different to relentless idea, or t'other way round, obv the americans are wrong. Anyway yeh i have a blow i cant get rid of no matter how tight i do the sleeve.



Consider this, cut the decat/cat pipe where it is 2.75 inch, i.e where it reduces, and get a straight piece of 2.75 welded on, and the v-band both the downpipe and the miltek. Hey presto, 3inch-2.75inch all the way that will never ever leak or blow. V-band ftw

That's my plan

 

[ShaunS3]

You won't be able to run a straight pipe from the DP to the back box as the rear diff/haldex is in the way... bends in pipes do slow down air speed but on a 3" system at your power levels it is largely irrelevant...

The standard system is fairly bend free up to the back box.... here is my 3" system next to the OEM system

I changed this later as it was too loud on the poxy little back box...

...although I did try a full on straight through system for fun ;P

Don't get too hung up on it... Miltek systems are 2.75" OD IIRC and 3" is plenty for 500+ hp

<tuffty/>

Cheers tuffty.

I will be using some of the angle bends from the milltek donor centre section but when I said 'straight through' what I meant was as straight as possible with the resonator box removed also.

The pipe I'm using is a 5ft straight pipe with an OD of 2.75'' to match the Milltek and will be welded up to the sports cat which is 3'' iirc.

I am going to try and cut into the reducer where its at 2.75'' so I can weld my pipe to it rather than back to 3'' and have to sleeve and create a weld reducer if that makes sense?

 

[darren t]

I have done exactly the same as you are explaining exactly the same setup mate it sounds awesome too be honest I cut out the resonated section of miltek and replaced with straight pipe it's biggest restriction is the miltek back box in my opinion but without it it sounds too much lol chavvy as you can get!!! Miltek non resonated is good!

 

[Andrew@A.L.D]

Don't get too hung up on it... Miltek systems are 2.75" OD IIRC and 3" is plenty for 500+ hp

Not a big fan of the Miltek myself, few months down the road after mapping i'm finding my back box is starting to die finding the wadding from insides of my back box over my boot lid.

here is what Pipewerx said to me

We could only do a custom build for this which we can do for £475 all in​

fitted. I think you will notice a lot of difference if you change the systemas the miltek is a chambered box as well as it being 70mm. at that power it

needs to be straight through box's and a minimum of 76mm.​

 

[superkarl]

Thats a good price from them andrew.



Does Anyone else think their miltek gets insanely hot??

 

[StaceyS3]

Mines melted my bumper above the two tips lol

 

[ShaunS3]

Not a big fan of the Miltek myself, few months down the road after mapping i'm finding my back box is starting to die finding the wadding from insides of my back box over my boot lid.

here is what Pipewerx said to me

What mods are you running and what stage of map?

 

[Jason.s]

Read his sig...says it all really lol.

 

[ShaunS3]

Read his sig...says it all really lol.

Can't see it on my phone :/

 

[s3clarke]

Signature says this Shaun: Maybe the most powerful Audi 8L S3 on this forum?
2067cc 20v GTX3076r Audi S3 now with 510+bhp. More to come.. 1150cc's injectors + More Boost = 570-590 bhp
OEM ECU Mapped Launch Control & Anti-Lag/Full Throttle shifting
3 Adjustable maps, GPS speed of 182mph so far

 

[darren t]

Signature says this Shaun: Maybe the most powerful Audi 8L S3 on this forum?
2067cc 20v GTX3076r Audi S3 now with 510+bhp. More to come.. 1150cc's injectors + More Boost = 570-590 bhp
OEM ECU Mapped Launch Control & Anti-Lag/Full Throttle shifting
3 Adjustable maps, GPS speed of 182mph so far

must have a video too back this up?????? as if i had spent that much id have loads of videos as evidence didnt you video the dyno???

 

[darren t]

that flat shift you have is it a wotbox?i bet the gear change is harsh!

 

[ShaunS3]

Audi S3 now with 510+bhp. More to come.. 1150cc's injectors + More Boost = 570-590 bhp

No wonder its red hot....running 500+ bhp through a box made for relatively standard spec models. Talk about pushing the limits!

Personally if I was running over 500bhp, one of the first things I would do is have a custom exhaust system designed and built to cope with the power.

Don't think Milltek will suffer half as bad on a stage 1-2 sub 300bhp S3....

 

[Jason.s]

must have a video too back this up?????? as if i had spent that much id have loads of videos as evidence didnt you video the dyno???

Look in the video section at the top of this section

 

[darren t]

Look in the video section at the top of this section

i have seen a video of his dosent look like 510bhp dyno video is hard evidence without this i couldnt belive lol i hope it is pmsl as it looks like mine lol minus the gt30 turbo lol

 

[ShaunS3]

Look in the video section at the top of this section

*Goes to watch videos on full pc screen*

 

[darren t]

*Goes to watch videos on full pc screen*

im not saying it isnt but video is not the best and id have videoed the actual dyno run id like too see a launch 1 2nd and 3rd gears that would be nice!!!!

 

[badger5]

...although I did try a full on straight through system for fun ;P

<tuffty/>

niki style............... haha

damn.. how old is this pic? no bench in the back ground!

 

[badger5]

Not a big fan of the Miltek myself, few months down the road after mapping i'm finding my back box is starting to die finding the wadding from insides of my back box over my boot lid.

here is what Pipewerx said to me

even our lupo is 3" full bore turbo back, x3 box system... 89db(A) @ 4500rpm

 

[superkarl]

Didnt tuffty have high egts limiting power with his miltek, hence why he went 3 inch.

Imagine the improvement on andrews car!

 

[badger5]

Didnt tuffty have high egts limiting power with his miltek, hence why he went 3 inch.

Imagine the improvement on andrews car!

yep..
its all about the flow - innit

 

[ShaunS3]

yep..
its all about the flow - innit

What rear silencer is tuffty running?

 

[superkarl]

What rear silencer is tuffty running?

miltek, but his is 3 inch all the way with the box opened up to take it

 

[ShaunS3]

Didnt tuffty have high egts limiting power with his miltek, hence why he went 3 inch.

Imagine the improvement on andrews car!

I can imagine EGT's being high on big powered applications such as tuffty's and Andrew's but for my low 'sensible' power spec I don't think I need to worry about extremely high EGT's like they would need to.

 

[badger5]

I can imagine EGT's being high on big powered applications such as tuffty's and Andrew's but for my low 'sensible' power spec I don't think I need to worry about extremely high EGT's like they would need to.

#

egts on yours would be higher I predict... its less well flowing by some margin...

 

[ShaunS3]

#

egts on yours would be higher I predict... its less well flowing by some margin...

Surely not to a point where it becomes necessary to upgrade the rear silencer from a Miltek?

Mine is a stage 1 with turbo back system and I don't plan to go for crazy power figures. The car is to be used daily with an occasional spirited drive.....surely EGT's only become an issue for me if being used for prolonged hard track use for example.