The difference on the A4 is it splits halfway up and exits through two seperate silencers giving better flow.

The TT has one rear box regardless of tailpipes. And they are a straight swap.

It's a marketing thing.

TT's are all about image!

People buying TT 225 and above, have to have some cosmetic differences to show the neighbours that they can afford the "better model"

The same is said for the TT 3.2 V6. They have a slightly different grill, rear black plastic diffuser and a little lip on rear spoiler just to show that it's different to the "lower spec" models

Not True! You can Spec a Twin Pipe on a FWD TT, Factory order Only! Audi will then Relieve your wallet of Nearly

Aye, but You still the need the Bumper with the extra cut out!!

It has to be said, the single pipe TT does scream "base model" and looks a little naff TBH.

I have seen twin pipe cars in the cold where condensation only comes out of one, then both a few minutes later, there must be more than cosmetics involved with that? Is it to do with controlling exhaust back pressure at certain revs? Or just the exhaust note like the Aston Martin V8 Vantage??.

Some BMW's have valves in one of the twin outlets that can be seen opening and closing in traffic if you catch it in your headlights.

Aye, but You still the need the Bumper with the extra cut out!!

Only the centre panel section.

Personally I don't try it on with any TT :(