Just out of curiosity, what is the affect on mpg with typical chip upgrades (APR, GIAC, etc....)?

 

The chips typically lean the fuel out, so they claim that the fuel economy is better with the chip. However, most people end up with a heavier foot so it might not actually be that way :-D

 

So are there any known downsides to the chip?

 

There hasn't been any known reliability issues documented, although, I would recommend monitoring the things more prone to failure more closely (biggest example of this would be the cam follower for the fuel pump).

The fuel economy is not reduced any unless you push the pedal harder.

They have been out for a while, so if anything had been known it would be well spoken about.

The only thing negative is that some dealers may report you to Audi and refuse to do warranty work. You would be best advised to talk to your local service advisor about it if that concerned you.