3.5" downpipe

[Kieran1990gti]

Been offered a custom 3.5“ downpipe off a mate for pennies, I thought they only went to 3" is it worth a purchase it's a full decat downpipe

[Dan_FR]

Depends on the car and what mods/stage of tune really

On a stage 1 or 2 GTI, i'd say not to bother and stick with a 3" DP... If you're Stage 2+ K04 (Ed30) thenit would be worth an upgrade if it's cheap enough

Plenty of companies out there jumping on the 3.5" bandwagon now

[Kieran1990gti]

Would there be any benifits at all to run a downpipe that size on a stage 1 as getting it for 50 notes, did get me thinking

[pudding]

3.5"?!?  Jesus, it's a 2.0, not a 5.0 V8!

That will kill the bottom end torque.   Even 3" blunts it a little off boost.

[Dan_FR]

It depends what your end goal is really

Peak performance on boost, or off boost drivability. It's not going to have that much of a detrimental effect over a 3". The huge impact is the de-cat downpipe over standard.

Bigger is better when it comes to maximing power from a turbocharged car though. When you're on the limits of the compressor map, any restriction at all will hinder peak numbers.

People have a similar argument on UK-MKIVS when it comes to the standard airbox. They think that just because a large turbo'd car, or the 3.2 V6 can pull north of 230hp through it, then it's not needed on a smaller turbo like the K03s, which hits a wall at around 220hp from memory, and needs an unrestrictive filter to make further power

[pudding]

Indeed.  Bigger is better, usually,  in terms of peak numbers but I prefer to look at the bigger picture.  Anything that adversely affects off boost performance is poor value imo, but mainly because 90% of my driving is commuting.  For those who aren't bothered by quick response low down and / or refinement, there can be benefits further up the rev range.

I remember in my R32 days, everyone thinking the OEM cats were Satan's work and robbed the engine of power and torque.  Wrong!  Nearly everyone who binned them in favour of decats of 'high flow' cats complained of a lack of torque low down.  Sometimes a restriction is beneficial!

3.5" would be better suited to a big turbo conversion where absolutely zero restriction downstream of the turbine would yield the most gains.  The stock K03 and K04 I think VW already did a half decent job of, less that pre-cat of course!

[AJP]

3.5"?!?  Jesus, it's a 2.0, not a 5.0 V8!

That will kill the bottom end torque.   Even 3" blunts it a little off boost.

My 3" downpipe has increased response off boost. Definitely not blunted it and there isn't any loss of torque.

Agree that 3.5" is possibly overkill for a k03 car, and the majority of k04 cars. It'd be beneficial if you're really chasing power; TTE420 or big turbo ballpark.

[pudding]

3.5"?!?  Jesus, it's a 2.0, not a 5.0 V8!

That will kill the bottom end torque.   Even 3" blunts it a little off boost.

My 3" downpipe has increased response off boost. Definitely not blunted it and there isn't any loss of torque.

Agree that 3.5" is possibly overkill for a k03 car, and the majority of k04 cars. It'd be beneficial if you're really chasing power; TTE420 or big turbo ballpark.

Which 3" DP did you use and do you have before and after dyno plots?  Not doubting you, I just want some data to work from as the decent pipes are expensive.

[AJP]

3.5"?!?  Jesus, it's a 2.0, not a 5.0 V8!

That will kill the bottom end torque.   Even 3" blunts it a little off boost.

My 3" downpipe has increased response off boost. Definitely not blunted it and there isn't any loss of torque.

Agree that 3.5" is possibly overkill for a k03 car, and the majority of k04 cars. It'd be beneficial if you're really chasing power; TTE420 or big turbo ballpark.

Which 3" DP did you use and do you have before and after dyno plots?  Not doubting you, I just want some data to work from as the decent pipes are expensive.

Powervalve. 200 cell cat.

Currently running that on Stage 1 R-Tech but I'm going down to see Niki to tweak the map in a couple of weeks.

Will get you an 'after' dyno once that's done, and there is a 'before' dyno knocking about somewhere... Bear with me.

[AJP]

Here you go.



That's Stage 1, stock hardware.

Remind me in a fortnight and I'll get you a pic of the next graph. This should show Stage 1 map + exhaust as well as Stage 2 map + exhaust. So you should be able to get the info you need from all the graphs.

Hope that's helpful mate

[AJP]

Just to add (as I can't verify with graphs just yet), the throttle response is miles better with the full Powervalve compared to the oem system, not just on full boost but down at low revs too. Seat-of-the-pants-ometer says the turbo spools much better.