Not too much. My average, according to MDrive is 13.5 L/100km. That was a 800 kph drive, averaging ~120-130kph. A "few" hard accelerations, and a couple of steady drives @ 130-140 kph. I tried to vary the speed/rpm as much as I could, but it was hard to do with a 800 km highway drive home.
All in all.......I don't care what the fuel economy, or the apparent lack there of ! , is!
'08 M3: AA G2L3, Catless X-Pipe & Sig Series Rear. AP rods. TC Kline EDC Coil Overs. MRF Alum Sub Frame Bushings. TMS Delrin Diff'l Bushings. BFI Motor Mounts. Recaro PP. BMW Perf Steering Wheel. P3 Gauge. PS Overflow Kit. APEX ARC-8 18"x9.5"/10.5". Conti Slicks 275/35F 305/30R. Stoptech Pads/SS Lines. Cantrell Brake Ducts.