What do you drive and what is your fuel economy... I mean calculated, not just the estimated instant readings that you get off the dash.

You can use the handy link I came across to convert to what makes sense to you.

http://www.onlineconversion.com/fuel_consumption.htm

My 2004 Allroad (2.7T (not-chipped)) seems to be getting ~12L/100km on the highway at about 120 kph. That translates to about.

19.6 MPG (US gal.)
23.5 MPG (IMP gal.)

What do you get?

 

I drove 2K miles in my 2K S4 and got @ most 28mpg HWY and 450 miles on 1 tank. (neutral going downhill helps) @ the time I only had K&N and straight 2.5" Al pipes. Now @ stage 2 I cant say HWY but city I get 20mpg.