d15b7 9.2=1 comp w/ an a6 head that has i believe 7.2cc worth of volume per cylinder, will up your stock compression to around 10.5=1 overall motor comp. Both have a 75x90 piston, where as the a6 block has 9.01 pistons. I have built many b7 a6 motors and best yet at the track is a 15.3, i dont care what anyone says that bitch was peppy as all hell, i loved it. of coarse you'll need a couple of things, intake, pm6 dizzy alittle bit of wiring, pm6 ecu yatta yatta, best bang for your buck 100%