Does a downpipe make a difference? Part 2

[SuckSqueezBangBlow]

Thats it... I am selling my brand new Corksport Downpipe I got coated with ceramic... just gotta get to 150 posts!

[Lex]

Originally Posted by Cheapspeed I'm stuck around 320whp on my 3076. High flow cat, resonated testpipe, and stock catback. Also, low compression in cylinder 3. But I'm definitely leaning towards opening up the catback now. I keep reading that I'm leaving about 15hp on the table, which seems to line up with your numbers.

This is about right but if cylinder 3 is hurt it's probably at least part of the issue.

[Jetfire]

Hoping a DP has some utility on the new CS turbo as I just dropped in a Cobb DP with it when my K04 decided that it deserved a line in my budget named oil consumption, but if nothing else it makes the car sound cool... : /

[zenit]

Originally Posted by Mike@Stratified

Food for thought:
Vdyno from 09 juan-
Both oem cats
OEM tmic
4" htp intake
E25-E30

AFR line has lb/min data in it.

[macdiesel]

That's a tasty morsel @zenit;


Sent from my iPhone using Tapatalk

[MSMS3]

It seems most of the people claiming a 3" downpipe produces no gains on the K04 are running E25 or other higher ethanol fuel and ethanol specific tunes.

That data may not translate to the same conclusion for those of us who do not have ready access to ethanol blends and are running pump gas 93 octane.

On pump 93 I experienced significant gains with a 3" catless dp/rp, a CAI intake and a modest tune, reaching 300/300. That's about all you can squeeze out of the stock turbo without adding more ethanol.

My datalogs support a significant gain from increased exhaust side flow upstream (3" dp and rp) when limited to pump gas and the stock turbo.

[sharksinspace]

Originally Posted by MSMS3 It seems most of the people claiming a 3" downpipe produces no gains on the K04 are running E25 or other higher ethanol fuel and ethanol specific tunes. That data may not translate to the same conclusion for those of us who do not have ready access to ethanol blends and are running pump gas 93 octane. On pump 93 I experienced significant gains with a 3" catless dp/rp, a CAI intake and a modest tune, reaching 300/300. That's about all you can squeeze out of the stock turbo without adding more ethanol. My datalogs support a significant gain from increased exhaust side flow upstream (3" dp and rp) when limited to pump gas and the stock turbo.

The comparison here is catless downpipe/testpipe vs catless testpipe only. Of course there are gains to be found by removing either of the cats (particularly the second) over stock exhaust; the question is how much additional gain do you see by also deleting the first cat after already having deleted the second.

[MSMS3]

Originally Posted by sharksinspace The comparison here is catless downpipe/testpipe vs catless testpipe only. Of course there are gains to be found by removing either of the cats (particularly the second) over stock exhaust; the question is how much additional gain do you see by also deleting the first cat after already having deleted the second.

But, the comparisons being made are with E25 or higher tunes. I'm saying the extra cylinder cooling effect of more ethanol, allowing higher boost and timing at leaner AFR must be accounted for. The extra ethanol is letting the higher boost at redline max out the turbo anyway.

On pump gas, we can use the extra exhaust side flow to increase lower - not as well as higher ethanol, but better than with stock dp/rp.

[sharksinspace]

But you talked about how you saw gains by going to 3" DP/TP together, which, well...obviously. The discussion at the heart of this thread is how much additional gain was it versus just a 3" catless TP. I'd also be curious to see a 93 comparo in addition to the E mixes, I'm just taking umbrage with the way you're relating it to your jump from stock exhaust to a 3" long DP, having skipped the step in between of running only the TP.

[zenit]

Originally Posted by MSMS3 That data may not translate to the same conclusion for those of us who do not have ready access to ethanol blends and are running pump gas 93 octane.

Originally Posted by MSMS3 On pump gas, we can use the extra exhaust side flow to increase lower - not as well as higher ethanol, but better than with stock dp/rp.

I agree with you on this. Tuning 93 is a different beast, and is far more sensitive to heat, and I can imagine that anything you can do to help move the exhaust charge away from the combustion chamber (i.e. removing restrictions) would help remove heat, too.

Originally Posted by sharksinspace The comparison here is catless downpipe/testpipe vs catless testpipe only. ..... the question is how much additional gain do you see by also deleting the first cat after already having deleted the second.

The no cat vs 1 cat debate was the purpose of this thread; however, based on my data above I'd like to propose a followup question- with a K04, E mix and a large intake- can you keep the exhaust stock (both cats) and see comparable power numbers with those who have 1 or 0 cats?
I think what @Lex; has said earlier in the thread supports this idea:

Originally Posted by Lex .... the k04 can't be spun much faster regardless, and the majority of the pumping losses come from the small turbo hotside and turbine.

^ that's not to say there are no gains with going test pipe/downpipe on the K04&E mix, but I'm thinking that the stock exhaust pieces (both cats) can create a hotside pressure differential sufficient to spin the turbine/compressors wheel up to and maintain maximum wheel speed through the engine rev range (3-6.5k) @ 100% WGDC.

In short- I'm suggesting that due to the smaller size of the housing and turbine wheel, the K04 doesn't necessarily need a much larger hotside pressure differential created by replacing or removing OEM exhaust components.

I think that there's some evidence too with @JgamB;s post with the BNR which has a larger turbine wheel- and maybe a K04 based hotside, depending on which version it is. He saw substantial gains not seen in this thread's K04 comparison from upgrading to aftermarket catless DP, particularly at the top end of the rev range. Perhaps the larger turbine wheel needs a larger hotside pressure differential to maintain wheel velocity at the top end?

With my work on the modified K04- which is using a ported hotside and a larger turbine wheel, I'm beginning to believe that I may have to uncork the exhaust a bit (a larger hotside pressure differential) to get maximum speed/flow from the turbine wheel at the top end of the rev range.

[Lex]

There are 2 things to consider.

1. Pumping losses. The easier it is to get exhaust out, the less power you lose doing so. This is a bit of a moot point on turbo cars as the turbo acts as a really big restriction.

2. Pressure differential across the turbine. The higher the differential the more energy you can put into spinning the turbo. This means higher turbo speeds and response times. This is where most see gains - with a catless setup the pressure differential across the downpipe increases and allows you to put more energy into the turbo.

[MSMS3]

Originally Posted by sharksinspace The comparison here is catless downpipe/testpipe vs catless testpipe only. Of course there are gains to be found by removing either of the cats (particularly the second) over stock exhaust; the question is how much additional gain do you see by also deleting the first cat after already having deleted the second.

Forgive me for seeming or being dense. I realize the comparison being made. My point is that the comparison is on cars running higher ethanol blends. I believe that for those of us running pump gas, adding the catless downpipe helps us more than those running ethanol blends, because you are already close to maxing out the K04. We need the extra exhaust side flow to compensate for the greater cylinder cooling, higher boost at redline without knock you are getting from the extra ethanol.

[sharksinspace]

Originally Posted by MSMS3 Forgive me for seeming or being dense. I realize the comparison being made. My point is that the comparison is on cars running higher ethanol blends. I believe that for those of us running pump gas, adding the catless downpipe helps us more than those running ethanol blends, because you are already close to maxing out the K04. We need the extra exhaust side flow to compensate for the greater cylinder cooling, higher boost at redline without knock you are getting from the extra ethanol.

Nah man, I dig it; maybe my undies were bunched that day to be such a nitpicker. I totally agree with you about wanting to see this same comparison done on pump gas tunes; even if the final conclusion is the same, it'd be nice to know for certain.

[MS3Zoom24]

So on the topic of this thread.

I have all mods that are in my sig and feel that my little K04 pulls really good.
Self tuned to 19.5 tapering to 17 @6k I typical Via AP show peak about 20.2 with 308g/s, Now from reading this thread it seems like I'm flowing really good?, NO?

Anywho I was debating on getting DP, but doesnt seem it is worth it. Going to get A CNT CBE cause I want it for sound, but My question is IF I upped my Intake to 3-3.5 MAF It seems I would pick up more power g/s Per second but would that also drop my WGDC since it would be flowing more g/s making Boost Achieved more Easily?

Does that sound about right?

Also trying to find a local e85 but having trouble finding one. since that seems to be some very easy power made


Thanks

[joecg1996]

so confused as to why people buy such expensive downpipes. i got mine for 125 and it does the same thing :/

[nindoja]

Originally Posted by joecg1996 so confused as to why people buy such expensive downpipes. i got mine for 125 and it does the same thing :/

Because not all downpipes are the same. Different flange designs, different fitment, different ease of install.

[sharksinspace]

Could be wrong, but I believe the Corksport DP is the only one that offers a 'divorced' design; so if that's someone's preference, they have to pay a bit more for it than an ebay special.