Took a short trip this weekend in my 2011 Mustang GT base. I have an SCT tune, on the way over I used the stock tune and got 19.3 miles per gallon.
on the way back I down loaded the Performance tune and got 24.2 miles per gallon.
The trip was approx 250 miles each way, on the way back I used the air conditioner most of the trip.
Has anyone else had these kind of numbers?

 

I assume the trip was mostly highway? I'd guess 19.3 was just calculated oddly by the car computer thought since that would be really low for highway driving. The tune does definitely increase mileage but in your case maybe there was a significant headwind on your trip there?

24-28mpg is common for highway mileage of the 5.0, and awesome for how much power is under the hood.

To be honest gas mileage has so many variables its hard to isolate causes of these things.

 

This is the second trip I've made in the last couple of months, same route. Trip is mostley on I-5. Used the same tune however, just reversed the tune. Performance tune on way over and stock tune on way back. Basicly same difference in mileage.
I'm going to get ahold of Bamma SCT and see what they think.

 

Did you calculate using actual mileage driven vs amount of fuel added? I usually get about 24 mpg going 80 on the interstate, no tune.

 

Used the computer calculater on the car.

 

You can't judge your average fuel mileage based on 2 data points. 200 is more like it. One tank of fuel with ethanol will yield different results than a tank of straight, non-ethanol laden gas, even if the engine is sitting in a lab let alone all the variations that can occur in real-life driving. Road texture, wind speed and direction, temperature, humidity, average cruising speed at certain engine RPM's, your foot; all play into it.

The on-board is typically inaccurate by 1-2 MPG (at least on the 05-10's) although there are a very small few who's on-board is darned close to dead-on. Hand calculating at each fill-up is the only proven, accurate method. And asI ststed above, it takes many, many data points to get even a warm fuzzy of what your car's average fuel mileage is. But if you insist on using the on-board, be sure to reset it at each fill-up.

 

Thanks for the information. I will start checking manually today(I need gas).

 

Reversed here:
First 8K miles I averaged 20.6 bone stock (18k on car)..... last 6Kmiles since I added 3.73and 93 Race tune 19.6. Just went up today from 19.5; driving good recently I have not reset my MPG trip since purchase last year.

 

By not resetting your on-board at each fill-up, you lose any sensitivity to current driving conditions due to how the computer averages. If you're MPG is reading 19.6 as an average over a year or whatever long time frame, you could be getting 30 MPG on your current tank of gas and it might show up as a tenth or 2 MPG increase (or conversely, getting chitty mileage and you might only see a 1-2 tenth drop). It will also mask any fuel-mileage-robbing problems you may have recently encountered.

Reset the onboard at each fill-up if you want to have ANY idea of your car's present performance.

 

I have a '10 w/ 3.73's. I am also running the 93 octane "race" tune. On the interstate on long trips, I am averaging about the same may be slightly less than the OP at 75 - 80 MPH. I have also averaged 20.2 @ 100 MPH, but that was with the computer. The other average was hand calculated.