Exhaust Back Pressure, A Little Help Is Needed

The Homacide

Registered User
If anyone can advise me i'd be very greatful.
The story goes like this, i was just about to pull onto the dual carridgeway and i heard a loud POP, i got a loss of power and then my exhaust was blowing like a good un. I pulled over and and looked under the car to find that the centre section had popped off the rear section.
I have a 1.8T AUM just been remapped by R-Tech Performance, i've got the usual mods, silicone TIP, high flow panel filter, 3" downpipe and decat, SAI removed, N249 bypass and PCV clean up and oil catch can added, S3 calipers and carriers.
My downpipe and decat goes into a standard exhaust, i'm wondering if this could be the problem and too much back pressure build up.

Has anyone else experienced this?
 

JonnyDerv

Registered User
I'm unsure about the back pressure theory. On my old tdi I removed the cat, back box and middle box (so straight through) to see if there was a power gain from less back pressure. Other than being ridiculously loud it was slower than before, I lost torque. Fitted a standard back box on again and my power went back up.

From my experience, you can have too little back pressure. Largest restriction is the downpipe, you've got a bigger one so I can't see how the silencers would cause too much back pressure.

Maybe check your turbo? When mine was on its way out it blew the boost pipes off the intercooler and broke it, including a replacement before I realised what it was, not sure if a knackered one would blow an exhaust like that though. Could simply be the exhaust failed.
 

The Homacide

Registered User
I'm hoping it's just an exhaust failure, it seems more like that than the turbo blown, as it was the sections that had come apart, then when I drove it to my mechanic it sounded like it didn't even have an exhaust on it, like a cavvy boy racer with a cherry bomb, the car still wanted to go but was too ****** loud. Anyway I'll find out tomorrow what the situation is. Thanks for the reply.
 

JonnyDerv

Registered User
Probably just the exhaust was failing then. Get that sorted and see how it goes, fingers crossed its all good :).
 

Jenno007

Registered User
from the tuners I've spoken to, on a turbo car you don't need back pressure, ideally you would just run a dump pipe with no mufflers or cat (if power was the sole purpose).

I'm guessing the loss of power is due to the tune not knowing what's going on?

I could be wrong, just what I've heard in the past
 

<tuffty/>

Badger 5 Edition...Its all about the flow...
Staff member
Moderator
Scanned for fault codes?

<tuffty/>
 

The Homacide

Registered User
No, my mechanic has the car at the moment, I'll ask him to do it for me, he works at vw so he'll have the proper scanner, see what he says. like jonnyderv said, maybe just the exhaust failing, just brie I brought it, it had a new centre section so maybe the garage that fitted it didn't do the clamps up tight enough
 

The Homacide

Registered User
No, my mechanic has the car at the moment, I'll ask him to do it for me, he works at vw so he'll have the proper scanner, see what he says. like jonnyderv said, maybe just the exhaust failing, just brie I brought it, it had a new centre section so maybe the garage that fitted it didn't do the clamps up tight enough
Tuffty is it possible that the gases can't escape quick enough through the exhaust
 

antwan64og

Registered User
Back pressure isn't needed like in a naturally aspirated car for scavenging but different exhausts can shift your power band.

Nissan WEC cars, lovely 5" dump pipes that let the exhaust wash around the wind screen

140150AD-7432-4B2F-A562-E91766773D1B_zpskiq9eusw.jpg
 

<tuffty/>

Badger 5 Edition...Its all about the flow...
Staff member
Moderator
Tuffty, it was dyno'd at 226bhp

Tuffty is it possible that the gases can't escape quick enough through the exhaust

Plausibly... but would expect you not to make that level of power... 226hp is fairly strong for a K03s, if the exhaust was restrictive then it doesn't appear to be limiting power at this point but thats not to say a free flowing exhaust wouldn't make a difference as it would..

As Bill always says... its all about the flow....

<tuffty/>
 

The Homacide

Registered User
Plausibly... but would expect you not to make that level of power... 226hp is fairly strong for a K03s, if the exhaust was restrictive then it doesn't appear to be limiting power at this point but thats not to say a free flowing exhaust wouldn't make a difference as it would..

As Bill always says... its all about the flow....

<tuffty/>
So do you think the map maybe a little too much power, it is a massive difference from when I drove it there, and thinking about it now it maybe is a little aggressive
 

<tuffty/>

Badger 5 Edition...Its all about the flow...
Staff member
Moderator
So do you think the map maybe a little too much power, it is a massive difference from when I drove it there, and thinking about it now it maybe is a little aggressive

Its making what its making mate... I can't comment on the tune as all cars respond differently and the mapping should have been done to work within the engines capabilities as thats the point of the custom maps... tbh most people change the exhaust and you would benefit from doing so anyway... lower EGT's and better spool/engine response typically

<tuffty/>
 

The Homacide

Registered User
Its making what its making mate... I can't comment on the tune as all cars respond differently and the mapping should have been done to work within the engines capabilities as thats the point of the custom maps... tbh most people change the exhaust and you would benefit from doing so anyway... lower EGT's and better spool/engine response typically

<tuffty/>
Its making what its making mate... I can't comment on the tune as all cars respond differently and the mapping should have been done to work within the engines capabilities as thats the point of the custom maps... tbh most people change the exhaust and you would benefit from doing so anyway... lower EGT's and better spool/engine response typically

<tuffty/>
Thanks tuffty, yeah I know I need to finish the exhaust off, but a ****** miltek is expensive and I'm skint now, it's there an alternative to a miltek, I've seen these 190 quid jobbies on eBay, are they any good for the money
 

<tuffty/>

Badger 5 Edition...Its all about the flow...
Staff member
Moderator
I think Prawn runs an eBay special... no experience of them personally so can't comment... its an exhaust, if the pipework is big enough (2.5" ideally) and the back box of a decent enough design then it will work... for how long is anybody's guess though :)

<tuffty/>
 

The Homacide

Registered User
I think Prawn runs an eBay special... no experience of them personally so can't comment... its an exhaust, if the pipework is big enough (2.5" ideally) and the back box of a decent enough design then it will work... for how long is anybody's guess though :)

<tuffty/>
Ah, I'll see if I can get hold of him and ask what there like, thanks, so is the back box the most restrictive part, or is it the whole cat back
 

JonnyDerv

Registered User
from the tuners I've spoken to, on a turbo car you don't need back pressure, ideally you would just run a dump pipe with no mufflers or cat (if power was the sole purpose).

I'm guessing the loss of power is due to the tune not knowing what's going on?

I could be wrong, just what I've heard in the past

That was my understanding before, the turbo doesn't need back pressure, but seemed to be the opposite on my old car :s.

Can't see how it not having map alterations for it would make a difference, it's just flowing better. Map wasn't altered for just back box delete, was much more responsive, abit more again with middle box removed, decat it went flat. Put a back box back on and it was much better again. Sounded ****** awful though haha
 

The Homacide

Registered User
Thanks people, seems like the restrictive exhaust is the issue, I'll get hold of prawn and see about the eBay special.
That was my understanding before, the turbo doesn't need back pressure, but seemed to be the opposite on my old car :s.

Can't see how it not having map alterations for it would make a difference, it's just flowing better. Map wasn't altered for just back box delete, was much more responsive, abit more again with middle box removed, decat it went flat. Put a back box back on and it was much better again. Sounded ****** awful though haha
 

Prawn

My other car is a MINI!!!!
I ran my old AUM daily with a 3'' DP/decat, tdi centre section, and a stock back cox for a long while.

It made 224bhp like that at Bills, and sounded like a jet engine due to the restriction of the back box.

I couldn't say for sure that the back box was costing it power at this point, as 224bhp from a st1 ko3S is still pretty mighty, but you could certainly hear the restriction.

On inspection underneath, you could actually see the heat related colour change on the decat as it stepped from 3'' - 2.5 - 2.25. With the 3'' section remaining a lightly bronzed silver finish, and the 2.25'' part going deep purple at the reduction point. It showed clearly that there was a build up as heat was really building up from here back.

In your case, it really does just sound like it's popped off randomly though. Stick it back on and enjoy it :laugh:
 

The Homacide

Registered User
I ran my old AUM daily with a 3'' DP/decat, tdi centre section, and a stock back cox for a long while.

It made 224bhp like that at Bills, and sounded like a jet engine due to the restriction of the back box.

I couldn't say for sure that the back box was costing it power at this point, as 224bhp from a st1 ko3S is still pretty mighty, but you could certainly hear the restriction.

On inspection underneath, you could actually see the heat related colour change on the decat as it stepped from 3'' - 2.5 - 2.25. With the 3'' section remaining a lightly bronzed silver finish, and the 2.25'' part going deep purple at the reduction point. It showed clearly that there was a build up as heat was really building up from here back.

In your case, it really does just sound like it's popped off randomly though. Stick it back on and enjoy it :laugh:
Ah nice one prawn, yeah that's a perfect example of the sound it makes, can I ask, why the tdi mid section, is it less restrictive
 

Prawn

My other car is a MINI!!!!
no mate. ebay silicon TIP, ebay 3'' DP, and a jetex filter were the only mods. made 224bhp. went well.for a daily :)
 

The Homacide

Registered User
That's good to hear, sorry to keep asking questions but is there anything I need to look out for with this engine, with regards to reliability issues
 
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