Coal Rolling is better
http://static.neatorama.com/images/2...-repellent.jpg

I still dump with my high flow cat and not just at tip in.

Meh, I am over that.

So.. @Mike@Stratified; @Lex; and @jbmazda6;

We should be seeing a dyno comparison with tuned stock dp vs tuned cpe catted dp yes?

On the same car?

Yes.

@jbmazda6; did you guys do any before and after dyno comparisons?

Im hopping on the dyno saturday. We will have to determine what significant gains are. I would say 15+hp to even make it worth buying. Thats just my opinion though and I believe I will achieve that Saturday. I will be writing up a full review of everything in my journey thread and will post up just an answer here.

We will also have to look at differences in temperature and humidity. Even though the dyno "corrects" for that, the car still runs differently in different weather (not a boost based tune) so that will have to come into consideration.

Thank you everyone (who is interested) for being patient.. the time has almost come.

We were able to get better stability before knock with the DP installed so the knock threshold was pushed out further. We will see the exact comparisons very soon.

Does the stock dp in this conparison have a race pipe?

No, full stock exhaust

So both the cats then? I think it would make more sense to have a racepipe/nator midpipe installed since that is the easier/cheaper option than a full downpipe install. Not to mention you should remove a cat in order to use a stage 2 OTS tune.

But effectively tp with oem cat is comparable to long catted dp stage 2 ots should be attainable

Cpe replaces both oem cats with 1 high flow cat.

The title of this thread is "does a downpipe make a difference", all but ONE of the options for the speed6 is a long downpipe so replacing the downpipe generally means replacing both cats. Its not saying whether a test pipe or downpipe is better. I have an opinion on that but dont feel like even touching on it until I see the numbers saturday.

Well downpipes usually eliminate both cats or replaces one of them with a high flow cat. So if the purpose of this test is to compare a stock downpipe and midpipe to an aftermarket downpipe with no cats or one high flow cat, I suspect that a 15 HP difference will be seen and I doubt anyone will disagree with that.

Most of the arguements I have had involves a stock downpipe + race pipe/NATOR midpipe vs any aftermarket downpipe, catted or not on a stock turbo.

Seriously, who is going to tune with both stock cats in the car?

I have seen dyno charts that show a stock dp/gutted test pipe can make comparable power to a full catless dp. Not the same car, day, weather, and moon cycle, but the results were there just the same.

They are buried in old threads, though, and I'm not going to search for them.

So... What happened to all these test results.

With so many people going to mid turbos, I can offer some data that won't mean much to the K04 crowd. Better than nothing I spose...

Same dyno, similar mid ~70F temps for all pulls. The E85 K04 setup was 68mm intake and test pipe only. The BNR S3 pulls were Gutted UPPER DP and stock test pipe vs ATP long catless. The results were impressive - so I would use the same train of thought we typically use for intakes - if you might go bigger later, you may as well go full 3" out the hiney now, unless you're concerned about expediting K04 seal failure.

http://i.imgur.com/9SKFPSSh.png

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.

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

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

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... : /

http://i1318.photobucket.com/albums/...psfibwly8w.jpg

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.

That's a tasty morsel @zenit;


Sent from my iPhone using Tapatalk

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.

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.

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.

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.

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:

^ 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.

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.

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.

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

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.

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.