I might be a little off on my thinking, but why would it go down. You are not introducing more fuel into the engine that you would at a the same rpm as a NA are you.
then again, I guess if you are having to ajust the fuel ratio then you would be changing the amount used.
My guess would be that you would see lower mpg because you would be on the gas a lot more. Thats would I would be doing at least.
A car with a turbocharged engine has a split personality when it comes to fuel economy as well as power. If you are just loafing along, you can get better economy than the normally aspirated version. On the other hand, if you spend a lot of time with your foot on the floor the fuel mileage will be terrible. The example that I had was my SAAB 900 turbo. Cruising on the interstate highway at 75 85 MPH it would get over 30 MPG. Lapping around the Hockenheim Ring it could go as low as 15 MPG. A friends normally aspirated SAAB 900 could get over 30 MPH on the interstate if he kept is down to 70 MPH. I dont know the worst he got but I doubt it was in the teens. That was the most extreme example but the same general thing happened with all the other turbo cars I have experience with.
I used to get 12 miles to the gallon with my 93 turbo miata...lol
But My foot was always mashed to the floor.
If I wanted dfuel economy I WOULD HAVE BOUGHT A HONDA cx OR SOMETHING
