Here is the situation. I ran the factory Diablo tune married to the Paxton 2200 with intercooler and the MPG meter on the GT said I was getting around 26 MPG as long as I drove very conservative. Friday I switched to a SCT x3 and a custom tune at Modular Power House in Cartersville Georgia and the MPG has dropped by 5-6 or so driving the same conservative style. Also, I have some fuel burning order I never noticed before the custom tune. Hard to complain too much as I picked up 40 HP after the custom tune... What's your experience?
I had just the opposite issue. I have the similar Vortech V2 (Vortech & Paxton are the same company). I had a custom dyno tune done, and gained 70 rwhp over the Vortech supplied tune, AND fuel economy improved by 3 mpg. It's one thing to tune for max power at wide open throttle, but a good tuner will also tune for cruise and partial throttle, as well. Take your car back for fine tuning on the dyno and your fuel economy can easily be improved.
