2.5" vs 3" downpipe.
 

before you get mad yes i search, i just want to clear up some myths

1:is it true that 3" well make me lose low end torque and its over kill big? if so how much we talking.

2:is it true i well over boost with a 3" ? <~~i think this is stupid my self.

3:if i do go 2.5" well this still work and perform good if i go BT or well i end up getting a 3" anyways?.

keep in mind when i say 3" i mean from the turbo all the way down to the down pipe a true 3" intel single solid piece. and when i say 2.5" i mean a test pipe you know those ebay ones and a down pipe 2.5" so a two piece.

i have a k04 with the pc16 file. i do plan going 28RS for sure.

any input is welcome.

1. this is bullshit. back pressure is bad. the bigger the better

2. this is bullshit. your wastgate controls the boost and it has nothing to do with your downpipe

3. what i would recommend is going no smaller than the outlet of the turbo. but bigger will be better. 2.5 would be ok for a 28rs but 2.75 or 3 will be better of course. keep in mind the bigger the turbo, the more air you putting into the engine, which also means the more air coming out of your engine. an exhuast will need to be sized to properly handle the extra air

sweet that's what i thought as well, so then basically ppl just guess and give misleading info. ok thank you then i guess i made up my mind going 3" for the win.

i just put on a 2.5 inch downpipe with 3" cat, then stock back, without the stock resonator. the turbo spools quicker, and makes more noise. im over all happy. cost me $50 from a guy

I have a 3" test pipe, down pipe is like 2.36 and the rest is 2.75 (I have a neuspeed catback)
Should I change my down pipe and what would you recommend that would bolt on?
Thanks

Only people I know who sell JUST a downpipe are Techtonics. It's 2.5" and will cost you $250 plus shipping. Even then, I don't know that it will bolt up to your exhaust, because it's designed to replace the OEM downpipe. Dunno about Neuspeed, but my exhaust has a different DP design than OEM. It's quite a bit longer after the lollipop hanger, where the OEM DP ends right there just behind the flex pipe, where the sleeve clamp that everyone hates is. I'd just leave what you have and call it a day, especially for a K03.

I'm k04 now, but I I think I'll just leave it like it is. Sounds good with the full exhaust and runs good.

Milltek makes a 2.5" downpipe for the 1.8T as well; it's made for Quattro, but I'm using it (currently without the hanger) on my FWD. And it's about $50 cheaper than the Techtonics:
Milltek Sport Downpipe AUDI A4 QUATTRO 1994 - 2001 1.8 MTKB5A4QDP

They would most likely drop-ship this part, and if they do it will likely come from England... so shipping may take a little while (but at least it's free!).