NefMoto

Hello,

I have a stage 1 tuned Audi TT MK1(8n, ME7.5) and I will replace the downpipe on it with a 3 inch without a CAT. The O2 sensor will be kept, but do I need to make any changes to the map, or can I do anything to get more performance?

I've never changed more than described in S4wiki

So usual rear o2 deletes and FKHABMN to 0

I think there is more possible, to also fix up BTS model but i'm not sure if its of any use

First assumption is that this will actually do anything for performance is already wrong.
It won't. The limitation is the tiny hotside of the turbo, not the exhaust.

Only thing it will do is make the car loud, and also not pass emissions of course.

3" DP is enough for 700hp. Completely unnecessary for this car.

Thats the reason why I asked. I just passed inspection, so I am good for another year. I am saving up for a race CAT, so next year this wont be a problem. I ve just driven the car and yea no real performance, but it does speed up and slow down a lot smoother. Throttle response feels also way better.

That does leave me to wonder, what is the use of a 3" downpipe into a 2.5" cat-back exhaust? Because to me this also seems rather unnecessary as flow would be restricted by this 2.5" anyway. Reason for asking is because it is an EXTREMELY popular setup.

Placebo is a wonderful thing. It does absolutely nothing apart from increasing noise. Your car with stock turbo 180hp? Is fine even with a 2.25" downpipe. 2.5" is enough for 380-400 hp. 3" is simply retarded on this engine. It's same way retarded as putting a giant 1 meter cone filter via a reducer onto a turbo with 2" inlet, except in the opposite way.

Helps if you are familiar with the ideal gas law and how gas volume reacts to temperature drop.

Commonly cited theory is that the larger diameter at the downpipe helps to disrupt the swirling flow imparted to the exhaust as it passes through the  turbine and transitions the exhaust to more efficient laminar flow through remainder of the (smaller) exhaust system. Volume of the exhaust gas also drops as the exhaust cools so a larger volume at the downpipe helps to compensate for the highest heat (and gas volume) found where it first exits the turbo.       

Well written but in the wrong order. You wrote what accounts for 5% (max) first and 95% second.
Exhaust gas post turbo is up to 850C, exhaust post downpipe tends to be already 150 deg cooler. Very easy to see on modern Diesel engines with three or more EGT sensors at different places in the exhaust.

Hello,
Sorry for a offtopic but i will be running 1.8t+efr7163 setup and my mechanic told me we will made a 3 inch downpipe, however my current exhaust is only 2.5 inch (with two end pipes) and we are wondering if the catback pressure will be too high. There will be 3" DP and reduction to 2.5" exhaust just after the subframe. In his opinion my current exhaust will bottleneck the power somewhere aroung 300-350hp. Is that true?

You need someone who understands how an engine works to make the project.
Just because you can weld an exhaust or rebuild an engine does not mean you have any clue about the combustion process.

Let me guess, you have no idea how to get it tuned afterwards either, in fact, that will probably be the last thing you think about and will be very surprised when nobody who is any good at this is interested, as they did not build it.

Nice ego you have there..

I am the one who drives it, just wanted to make sure my mechanic thinking is correct.

Thanks for nothing.

Find new mechanic or company. This one is clueless.
Also, my comment was extremely relevant. You have no clue about anything. You really expect that you are going to do a EFR7163 project with this level of knowledge?
Once you bolt all the parts together and nothing works, nobody will want to tune it. You clearly won't be able to do it yourself, so before wasting a ton of money, then selling the car for parts, go and find a company who can do the whole project from back to finish including the tuning.

Not a "mechanic", a tuning company.

Also, you are nobody to moan on here. Contribute 0.1% of what I have, then talk.
So far you have just asked a bunch of questions, most of which can be answered by search.

Sorry i disturbed your masturbating to the mirror, sir.

Sucker punch beginner who just wanted to ask for some basic stuff. your life must be harsh.

Over and Out :)

Hello gentlemen, I am not experienced in tuning because I have been playing and learning for 1.5 years, but I have 20 years of experience in mechanics.
From my experience with the exhaust in my car a3 1.8 t aum it comes out that the exhaust of the catalyst and the 3-inch pipe descending gradually to the original exhaust gives better flexibility in revolutions below the operation of turbo k03s, I do not know about larger turbines. My configuration is 3 inch pipe then factory center muffler then end pass with branching to blank silencer above it. Modified flight installed side water intercooler and whole installation cooler tank pump all under bumper. 320 injectors factory fuel pressure regulator 4bar.
The engine is mainly powered by propane-butane gas, boost in peak 1.2 bar, down to 0.8 at 6600 rpm, max flow from maf 164 g / s, max inlet temperature at external temperature 27st / c = 55st / c ignition +3 degrees in in relation to the series. I wrote through the translator, sorry and greetings.

Modified water intercooler factory mounted and complete radiator tank pump installation under bumper.

None of that gibberish makes sense.
Also by default a larger exhaust does not do anything for the low end whatsoever.
Flow depends on RPM and below 2000 RPM it won't make any difference whether you are using full stock or something else.
There's literally zero backpressure.