Is there an upgrade like this for the A3?

There must be some induction kits that have uprated air feeds, or at least models within the range that have larger OEM pipes (like he found out in the link). I'd guess the S3 has the biggest, but probably won't be a straight swap onto a diesel engine, and you've already got the best diesel (I think) so probably have the best OEM piece you can use. I'd look at other 1.9TDis on the same chassis that came with more power - some mk4 Golfs had 150bhp, that's probably going to be the best option.

This is all purely speculative, I don't have a clue if you'll have any luck, but that would be my best guess at a first step - find out if the airbox feed on a 150bhp Golf is a larger diameter than your own. The 150s had all red "TDi", by the way, and were only 2000-2003.

Good luck
 
your better off just running a 4" cold air duct from the front bumper to be honest, it wont look OEM but will definately work far better than anything standard
 
Its more the OEM look Im going for.

None of the other feeds for other chassis will fit unfortunately as the A3 feed goes much further into the wing, the 150s only have a restrictive pipe also as they all do the same upgrade and shown on the topic I posted.
 
you can run a cold air feed from your front bumper and use a hole cutter on your airbox and connect the other end upto that ;) if you fit it with a K&N panel filter aswell it works alot better than a induction kit :p