Check this out
 

<ul><li><a href="http://extrudehone.com/">http://extrudehone.com/</a</li></ul>

Replica Maschinen Inc. does a similar polish/thermal coating
 

on the the intake manifold and head along with valve work. They got 24 cfm/cylinder airflow improvement on a stock Miata and a 30hp increase. I don't know how this would work on a TT or what effect it would have on the air tumbling process Audi uses to get a better combustion. Cost about $1500.