vtraudt

"Motor out" is coming up.
Currently stage 2. Will get K04 turbos.
Have gutted pre cats and main cat delete. Stock exhaust.

Down the road, full stage 3 (trying as much as I can to maintain good low end even at the expense of high end horsepower).

With the motor out, I am wondering if I should get larger downpipes.

I have learned that back pressure is NOT universally bad. Part of the quick and early spool we all know from stock Audi turbos (1.8T as well as 2.7T) can be attributed to the back pressure created by the tiny hot side, manifold and exhaust path.

Question:

How does 'gutted pre cat stock pipe' compare to the offered aftermarket down pipes with respect to flow, spool up, EGT?

How restrictive are they compared to 'big' down pipes?

MDJ

Stock DPs or piggies are more restrictive than say 3" or split DPs simply due to their size. I noticed a drastic reduction in spool up once they were installed.

As for EGTs, you have a GIAC tune. They are notorious for 'dumping' fuel in their tunes (not like everyone else doesn't do it too). The EGT sensors in our cars are meant solely meant to detect a lean AFR and protect the engine by adjusting timing and boost. Now that you are going to be stgIII tuned, you don't need to worry about EGTs or the stock sensors. In fact, I have mine coded out along with the secondary O2s.

vtraudt

Couple questions:
a) what are "split DPs"?

b) 'drastic reduction in spool up": are you running K04 turbos on your setup where you experience it? (Side note: any VAGcom logs before/after (MAF, Boost, etc.)?

c) EGT: 'meant to detect lean AFR and protect': That sound like something I don't want to give up. You suggest that Stg III tunes do away with that protection. Why? Why not use them?
Particularly since I may not go with an 'off the shelf' tune.

d) My rear O2 are tuned out, because they do not (my understanding) "DO" anything (they are passive indictors only, not actively 'controlling' anything). Seems different from what the EGT sensors are doing ('active').

MDJ

Split downpipes are just that. 2 pipes off the flange going into 1 about halfway down the full length of the header. They sound absolutely amazing. Labree makes them. If you search you tube you can find a video of a nogaro with full Labree exhaust. Kinda pricey, buy good stuff. I'm not sure the performance is much better than 3" DP, though.

I meant reduction in spool up time. Quick spool up.

What I meant about being tuned and your EGTs is that you're far, far, far more likely to see a rich condition with a stgIII tune than lean because of the fuel mapping. EGTs are really only necessary on stock tunes, IMO. You'll find others that disagree. Mine are coded out.

The rear O2s are basically only checking flow vs. The primarys, which you need. EGTs are only temperature probes. Should the exhaust temps be too high, its 99% of the time a lean condition. If you're stgIII, id expect you to know about AFR's and have a gauge. No need for EGTs! They're just pesky saftey devices that always break and cost waaaaay too much money.

vtraudt

On K04? Do you have data logs showing the difference?

AFR gauge is the key word (no EGT sensor and no AFT = flying blind = risky business). But having a 'saftety net' is nice; and yes, they are pesky and expansive (recently change one, and another is coming up soon (code).