I have a chipped 1.8Tqm, I am not going to upgrade the turbo. The only performance mods are a 1 bar chip, BPV and K&N--everything else is stock and will remain that way except the exhaust. In theory, which would give me the most noticeable improvment and pros/cons of each:

a cat back exhaust that has a 2.5" downpipe, and the rest is 2.75"
or
a cat back that is all 2.5" (dp included)

sorry, I have asked similar questions before, but spending $800+ is not something I want to do without good research.


thanks a lot,
Mike

more important. To your engine, the exhaust looks like a 2.5 inch (or 2.75 inch) tunnel with areas that are necked down to something much smaller than 2 inches; the muffler , resonator (maybe), sharp bends and even tips. If the muffler isn't free-flowing, it could flow no better than a 1-1/2 to 1-3/4 inch smooth pipe!

If all muffler manufacturers published flow numbers, especially relative to the flow through a 2.5 in tube, it would help us choose. Only a few do, and I don't think they make Audi systems.

European Car did a comparo of 13 systems for a 1.8T Jetta (see the link). Most systems gained some power, but at least one lost hp from stock! I had a little trouble with the dyno graphs; I had to drag the enlarged ones higher to read the hp & torque numbers, and close each one before opening a new one. Maybe it's just me.

This might not be an exact comparison for A4, but I suspect the mufflers, resonators, etc. from each of the sources would be very close to the Jetta system tested. You also get to hear them if you wish. It's a good read.

My $.02<ul><li><a href="http://www.europeancarweb.com/archives/tech/1101_tech00.shtml">http://www.europeancarweb.com/archives/tech/1101_tech00.shtml</a</li></ul>

Bigger is always better no doubt about that and as smallTTs mentioned mufler is important for turbo cars straight through mufler is the best little noisier but the best flowing.
I would go with the 2.75" but find out what kind of mufler it is and if it has anny resonators since most companies put smmaler inside pipe diameter resonators to keep the noise down.