Downpipe for K03

[Tallpaul]

This is a non model specific, general question based on a K03 turbo...

It's widely known the OE downpipe is the major restriction in the exhaust system; Based on this, would any improvement be gained by mating a Milltek 2.5" downpipe and 200cell Race CAT to the OE CAT-back system (~1.75 - 2"?)?

I know that maximum benefit would be gained from keeping the 2.5" straight through, but the cat-back Milltek is an extra £300, does the performance benefit justify the additional cost?

I don't really want to lose the discreet backbox/tailpipes my A3 has and i'm loathed to spend £300 on something i won't like the look of and gives minimul gains anyway... Of course if the downpipe alone won't do anything then perhaps it's a necassery evil.

 

[rsrich]

good question, one I want an answer to as well

Anyone with real figures?

 

[Tallpaul]

Not many people have before and after figures from just the exhaust.

I've seen claims of 15bhp and a healthy dose of extra torque from fitting the downpipe and CAT.

From my own experience, the full system was an (expensive) improvement on my old Leon Cupra, but i have no experience of the DP only.

From reading posts on uk-mkivs.net, people have fitted the DP/CAT alone with claimed benefits but no actual figures to assess the cost v benefit.

 

[acidstrato]

imo its pointless getting just the downpipe cos although that is the most restrictive part, the rest of the system will just restrict the more free flowing downpipe and to get the real gains of the downpipe you need the whole thing, otherwise its not worth the money

15bhp from the entrie system is pretty optimistic, but i def felt gains, just not much

maybe just consider a different catback system as milltek is one of the more expensive products. maybe jetex? or blueflame

 

[Tallpaul]

thanks fella, but statements based on opinion aren't much use...

I'm aware that the narrower bore of the OE CAT-back will be more restrictive than say a 2.5" straight through. But whether opening up that restriction will give any measurable gain is the question.

Plenty of Golf owners are running DP/CAT only, but i'm looking for hard and fasts here as £300 extra is a lot for a section of exhaust i don't even like the look of and am not convinced will give any significant benefit.

 

[rsrich]

The savage restriction at the entry to the downpipe from the turbine outlet is the part that does the damage on a std downpipe, in conjunction to a lesser extent with the lesser pipe diameter and restrictive Cat. It's quite feasible that drastically reducing the backpressure in the turbine at this point will greatly improve the turbine efficincy even on a standard system (I'm not convinced how restrictive the standard system actually is??), but would be great to get some proper data

 

[Tallpaul]

I agree, if you put the OE downpipe next to the Milltek 2.5" one the restriction is plain to see. The 'kink' in the bend of the OE almost halves the diameter.

For the amount of gas a K03 can actually flow i'd have thought the 2 inch-ish bore of the rest of the exhaust would be sufficient, probably for the K03s too

 

[acidstrato]

thanks fella, but statements based on opinion aren't much use...

I'm aware that the narrower bore of the OE CAT-back will be more restrictive than say a 2.5" straight through. But whether opening up that restriction will give any measurable gain is the question.

Plenty of Golf owners are running DP/CAT only, but i'm looking for hard and fasts here as £300 extra is a lot for a section of exhaust i don't even like the look of and am not convinced will give any significant benefit.

you wont find the facts your looking for here mate because most people dont do things by halves!!

i may have said that its my opinion to protect myself.. but at the end of the day it doesnt take a degree in rocket science to see its a bottle neck...just cos more gasses will flow through the downpipe...wont increase the amount that flows through the rest of the system, its always going to be limited hence a restriction

id even imagine there would be pressure problems.

no offence to every Golf owner in the world but I'm a member on UKMKIVS and they are certainly not the brightest bunch.

 

[rsrich]

it's quite feasible that the standard system isn't all that restrictive, just because it's a "standard" system.. without data it's unreasonable to say that.. However, it is quite fair to say that the downpipe/Cat IS restrictive because it's obvious looking at it.
Also worth remembering that a degree of backpressure is required to stop oil getting past the turbine seal in the turbocharger into the exhaust.

 

[acidstrato]

but my point is you wont find the results/evidence you speak of
especially when your on a seat forum

but at the same time theres more negative points against the standard systems anyway...mild steel for example so it'll rust and eventually break leaving you will a bill roughly the same price as an aftermarket system anyway

and the general opinion is that if you gonna pay that much money anyway, you might as well get a stainless steel system, which cant do any harm by being .50"/.75" larger

 

[Tallpaul]

you wont find the facts your looking for here mate because most people dont do things by halves!!

i may have said that its my opinion to protect myself.. but at the end of the day it doesnt take a degree in rocket science to see its a bottle neck...just cos more gasses will flow through the downpipe...wont increase the amount that flows through the rest of the system, its always going to be limited hence a restriction

id even imagine there would be pressure problems.

no offence to every Golf owner in the world but I'm a member on UKMKIVS and they are certainly not the brightest bunch.

looking at the system as a whole, and as mentioned in previous posts, the 'major' restriction is the DP - more specifically the bend. At this point the bore is reduced to less than at any other point in the system, perhaps except the CAT but the Milltek DP would take care of that too.

Whether you believe that only replacing the DP is doing it by halves or not is neither here nor there. The effect of only fitting the DP would not be detrimental and i believe that removing the largest restriction will be beneficial.

Of course removing the DP restriction means the CAT-back becomes the next restriction in the system, simply by virtue that the 2" bore is less than the DP. However, my point is simple: Is a 2" bore actually restrictive to the K03? I honestly doubt it, perhaps 2.5" is overkill for the DP (3" certainly is), but as that is the diameter that it comes in then so be it. In fact, it has been measured that there is a point in the Milltek DP where the bore becomes less than 2.5" (~2.1"?) but i know from experience that the extra bore of the Milltek system does give real gains (based on my old Leon Cupra).

Whether people are 'bright' or not is irrelevant here and a little childish to even raise. Just because other people don't want to spend £300 on a potentially uneccasery item or are simply wishing to maintain an OE look it there business. Why should posting questions looking for factual answers be a problem? If the answers don't come then OK, but that's no reason not to ask.

 

[acidstrato]

thats not to deny the fact the gains havent been seen from full systems

but at the same time I've not met anyone ever who replaced a header/downpipe on any car without uprating the rest of the system..might just be unfortunate not to have or it could just be because no-ones hard the fruits to try it

 

[acidstrato]

i'll stay zipped then

if you dont want to listen to my contribution then thats perfectly fine

i'll end by saying...if you honestly doubt it....then why dont you try it, as thats the only way you will know for sure

 

[Tallpaul]

then why dont you try it, as thats the only way you will know for sure

I probably will try it, but if somebody had the dyno plots/whatever to come along and say 'don't bother it 100% won't work'. Then i'd wait until i could afford the full system.

 

[CupraJay]

On my cupra, iv had a downpipe, sport cat and full system..stainless steel, mandrel bent corners.

And i felt..what id call..Minimal gain.. Could feel extra pull, but not wot you'd think..id say 10bhp...maybe. Im possibly looking at manifold next...complete the whole thing.