Gti vs golf downpipe

[breaking badly]

The stock DP isn't that 'awful' design as some think. Its cat (two cats in NA) is (are) restrictive,
not its 'inlet' or 'ellbow'.
Be assured Volkswagen used the most advanced methods including CFD to design it this way.
Be assured they tested it extensively. Contrarily most if not all aftermarket DPs are just designed
'big'. Sadly most aftermaket DPs even lack a heat shield. Remember there's the ABS/ESC hydro
block near the DP's 'ellbow'!

That said, GTI, Clubsport and R DPs are different. Both Clubsport and R factory DPs come with
a cast 'inlet'/'ellbow', while the GTI and GTI Performance as well as the 1.8 TSI use a cheaper
sheet steel part instead.

GTI & GTI Performance - stamped steel, note the 'flat spot':

Golf R and GTI Clubsport - cast:

I'd bet the CS/R DP is superior in terms of flow, however it's perhaps not worth the labour to
swap a GTI DP for a CS one (considered there are no cheap/used ones available in the US any-
way) or the R's. However it may be worth it for those few 1.8 TSI owners in Europe to fit a used
Clubsport DP.
On a side note: My very first picture is showing the revised Euro spec 7.5/facelift GTI Performance
engine (engine code DLBA) and that one obviously also gets the cast DP now!

 

[m3lonbr3ad]

The stock DP isn't that 'awful' design as some think. Its cat (two cats in NA) is (are) restrictive,
not its 'inlet' or 'ellbow'.
Be assured Volkswagen used the most advanced methods including CFD to design it this way.
Be assured they tested it extensively. Contrarily most if not all aftermarket DPs are just designed
'big'. Sadly most aftermaket DPs even lack a heat shield. Remember there's the ABS/ESC hydro
block near the DP's 'ellbow'!

That said, GTI, Clubsport and R DPs are different. Both Clubsport and R factory DPs come with
a cast 'inlet'/'ellbow', while the GTI and GTI Performance as well as the 1.8 TSI use a cheaper
sheet steel part instead.

I'd bet the CS/R DP is superior in terms of flow, however it's perhaps not worth the labour to
swap a GTI DP for a CS one (considered there are no cheap/used ones available in the US any-
way) or the R's. However it may be worth it for those few 1.8 TSI owners in Europe to fit a used
Clubsport DP.
On a side note: My very first picture is showing the revised Euro spec 7.5/facelift GTI Performance
engine (engine code DLBA) and that one obviously also gets the cast DP now!

Agreed about the elbow/inlet not being that restrictive, since it seems to open directly into the cat at the point that the elbow/inlet starts to look restrictive. The cats are the primary restriction which is probably why you don't see many(any?) carb/epa legal aftermarket downpipes for mk7 in US market. They simply won't look competitive in terms of hp/$.

Appreciate the information regarding cast vs sheet steel on those stock downpipes; I probably would have never noticed that detail.

 

[TwinDad]

I'll let my data collected speak for itself in regards to if the gutted stock downpipe works as well as the aftermarket 3". Like I said earlier, above 6,000 it does not pull as much. I just shift at 6,000 now. I think with the is12 that is probably best anyway. Also keep in mind that it was cooler on the 3" pipe run. The timing is slightly better. Mostly just above 6,000.

Here is my best log that I got with the gutted stock downpipe on e30
https://datazap.me/u/jcranwell/piggie-pipe-3?log=0&data=1-4

And here is one of the best logs that I got with the 3" downpipe on e30
https://datazap.me/u/jcranwell/e30-224-peak?log=0&data=1-4

 

[toledospeed]

I think with the is12 that is probably best anyway.

I agree...with the IS12, you really don't gain anything at the top end with an aftermarket DP. If you look at APR's stage 1 vs stage 2 1.8t graphs, you don't achieve higher max HP/TQ gains up top when you add their DP (even when the stock DP still has two cats in there!). It's an "area under the curve" mod that still helps nicely with acceleration in their tests, as we have discussed before. A perfect example of why looking at max gains only doesn't show the whole picture of what is going on.

What I would like to know is what the piggy pipe would look like on a dyno graph. Would it look more like the stock DP or more like the aftermarket DP with the 1.8t/IS12? Would acceleration testing show the same gains as with the aftermarket DP? Since max HP/TQ is not increased by adding the aftermarket DP on the 1.8t/IS12, one can argue that maximum exhaust flow isn't a limiting factor. However, one could argue that the optimized pipe design allows for better velocity and more efficient spooling of the turbo. I'm sure removing the first cat in the piggy pipe helps it spool more efficiently as well, but how much does it help as compared to a perfectly designed pipe?

Finally, if you look at what happens with the IS20\1.8t, adding the aftermarket DP starts to make a real difference up top, since flow is limited by the stock DP.

APR Reference:
http://www.goapr.com/products/ecu_upgrade_18tsi_gen3_mqb.html

P.S. Not arguing with anyone, just offering more food for thought! Lots of good data here. If we can run a gutted stock DP and get the same performance as with an aftermarket DP, that would be great. I just haven't seen any dynos or time slips to prove things one way or another.

 

[TwinDad]

I agree...with the IS12, you really don't gain anything at the top end with an aftermarket DP. If you look at APR's stage 1 vs stage 2 1.8t graphs, you don't achieve higher max HP/TQ gains up top when you add their DP (even when the stock DP still has two cats in there!). It's an "area under the curve" mod that still helps nicely with acceleration in their tests, as we have discussed before. A perfect example of why looking at max gains only doesn't show the whole picture of what is going on.

What I would like to know is what the piggy pipe would look like on a dyno graph. Would it look more like the stock DP or more like the aftermarket DP with the 1.8t/IS12? Would acceleration testing show the same gains as with the aftermarket DP? Since max HP/TQ is not increased by adding the aftermarket DP on the 1.8t/IS12, one can argue that maximum exhaust flow isn't a limiting factor. However, one could argue that the optimized pipe design allows for better velocity and more efficient spooling of the turbo. I'm sure removing the first cat in the piggy pipe helps it spool more efficiently as well, but how much does it help as compared to a perfectly designed pipe?

Finally, if you look at what happens with the IS20\1.8t, adding the aftermarket DP starts to make a real difference up top, since flow is limited by the stock DP.

APR Reference:
http://www.goapr.com/products/ecu_upgrade_18tsi_gen3_mqb.html

If I compare the whp charts on APR for 93 octane stage 1 vs. stage 2, There is almost no difference up top. Its mostly just the torque starts a lot lower. So it appears that they can just turn up the low end even more without it getting hot too fast. I'm getting the same amount of low end boost and timing with the gutted pipe vs. the 3". Numbers that I could not get on the stock pipe.

 

[MeltedSolid]

I'll let my data collected speak for itself in regards to if the gutted stock downpipe works as well as the aftermarket 3". Like I said earlier, above 6,000 it does not pull as much. I just shift at 6,000 now. I think with the is12 that is probably best anyway. Also keep in mind that it was cooler on the 3" pipe run. The timing is slightly better. Mostly just above 6,000.

Here is my best log that I got with the gutted stock downpipe on e30
https://datazap.me/u/jcranwell/piggie-pipe-3?log=0&data=1-4

And here is one of the best logs that I got with the 3" downpipe on e30
https://datazap.me/u/jcranwell/e30-224-peak?log=0&data=1-4

It looks like the key operational differences between those logs are that the piggy pipe one is at a much higher temperature (+20 F), and started later in the RPM range. Overall, the timing with the piggy pipe is lower but cleaner and the boost before 4000rpm is a tad lower. I wonder if you could push the piggy pipe further, you aren't getting any correction in ign 2-5 with it.

 

[Gawernator]

Melted solid I swear to god I’ll give you an entire large pizza if you do my JB4 today lol


Sent from my iPhone using Tapatalk

 

[MeltedSolid]

XD. Well, I can give you advice, but to be honest I am still learning. The only real data I have is my own car. That being said, you have basically the same setup as me except with a downpipe, so I could probably give you some good help . Have you started messing with any settings on the JB4 yet?

 

[Gawernator]

XD. Well, I can give you advice, but to be honest I am still learning. The only real data I have is my own car. That being said, you have basically the same setup as me except with a downpipe, so I could probably give you some good help . Have you started messing with any settings on the JB4 yet?

I haven’t had any time to physically install it. Or the side skirts. D:


Sent from my iPhone using Tapatalk

 

[TwinDad]

It looks like the key operational differences between those logs are that the piggy pipe one is at a much higher temperature (+20 F), and started later in the RPM range. Overall, the timing with the piggy pipe is lower but cleaner and the boost before 4000rpm is a tad lower. I wonder if you could push the piggy pipe further, you aren't getting any correction in ign 2-5 with it.

The problem I was running into with the piggie was my trims were through the roof and I was getting lean conditions. I had about 4 gallons of e85 in which I have done before. George agreed with me that it could be variances in the actual amount of energy 85. The first time it could have been been 70% and that time it could have been 85%. I then lowered my settings to compensate. After that I went and turned my FOL up to 75, but I didn't try higher settings before I needed to fill up again. Then I had to go back to 93. With the downpipe I was able to hit 23.1 psi peak and 18.5 at 6,000, but I started getting overboost occasionally so I backed it down to 17 at 6,000

 

[MeltedSolid]

I haven’t had any time to physically install it. Or the side skirts. D:


Sent from my iPhone using Tapatalk

bout time to get on that!

 

[MeltedSolid]

The problem I was running into with the piggie was my trims were through the roof and I was getting lean conditions. I had about 4 gallons of e85 in which I have done before. George agreed with me that it could be variances in the actual amount of energy 85. The first time it could have been been 70% and that time it could have been 85%. I then lowered my settings to compensate. After that I went and turned my FOL up to 75, but I didn't try higher settings before I needed to fill up again. Then I had to go back to 93. With the downpipe I was able to hit 23.1 psi peak and 18.5 at 6,000, but I started getting overboost occasionally so I backed it down to 17 at 6,000

Interesting. I wouldn't have thought that you would end up putting more load on the fueling system in that situation. I guess your trims are pretty much maxed out with both. Maybe it has something to do with the slightly higher backpressure? I have no idea.

 

[Gawernator]

bout time to get on that!

That’s where you and the free pizza come in

 

[TwinDad]

Interesting. I wouldn't have thought that you would end up putting more load on the fueling system in that situation. I guess your trims are pretty much maxed out with both. Maybe it has something to do with the slightly higher backpressure? I have no idea.

It could have been from a higher ethanol content, higher egt so fuel was being added or both. Once I turned up to FOL 75 everything looked ok with the AFR, but trims still high. I know with the higher egt from the is12, the ecu will add more fuel to compensate

 

[TwinDad]

So I got the gti downpipe in and it's a noticeable difference. It pulls strongly to redline the same as the 3" pipe did. The stock pipe would struggle above 5,800 or so. I was able to do a few logs and they all look really good. I do have a separate AFR issue, but I think I knocked the positap loose. Occasionally the AFR drops to 0.0 and the power drops a bit. It's random though. I'll do some more logs once I get that sorted out