So prior to going catless with the Gintani tune I took a day trip down I-95 in my M5, achieved 20-21 MPG cruising at 65-67MPH in P500-S3. After getting my car back from the shop; they only drove it 3 miles but let it idle to warm up, the MPGs dropped to 6 due to idling and not being driven enough to adjust. Since then I drove it to work twice which is 21 miles each way and my MPGs are up to 14. I’m sure they’ll continue to climb if I take another day trip. Again it’s based on driving habits and health of motor. Mine only has 53,500 miles and prior to catless plus tune my only performance-engine mods were Dinan WideThrottle Bodies, Dinan Underdrive Pulley, CF delete, secondary cat delete, Rogue X pipe and Eisenmann race mufflers.