Just filled up my 3rd tank of gas. Calculating manually, I avaraged 23.56MPG however, the computer says I only averaged 21.8MPG. Not sure if the computer will be that far off normally or not. My F150 typically reported within 0.5MPG and was usually maybe only 0.1-2 MPG off.

This was in mixed driving, good amount of idling due to traffic. 3.31 gears.

 

My 2011 3.7 is off about the same as yours.

 

I wouldn't count on the computer's MPG calculations being any better than within about ±10%, nor for any two cars taken at random to be typically "off" by the same amount.


Norm

 

MT with 3.31 here.

I had 1600 miles on and couldnt get better than 23mpg highway before my trip to TN. Fuel economy jumped up to 27 on the way home, but I had 2300 miles or so by then.

Pretty darn hilly in TN and KY, even on the highway, so im sure that hurts. I ran it hard just a little bit ago and it fell to 26.1.

There was only one tankfull that I checked by hand against the computer, and it was off by 1 or 2 mpg just like you guys.

 

I just drove 860 miles from north Carolina to mt pleasant Mich and loaded down six speed manual, 331' s 72 mph pretty much all them mountains got 30 mph 450 to tank, I am impressed. I do think that new bug deflector helps cause I have made 300 mile trips, 70 and nothing in car got only 28.

 

Forget the Stang. If you worry that much about fuel mileage, buy a Prius.

 

But Nuke, how do you REALLY feel?

 

MT6 with 2.73’s here (soon to be 3.31’s)

After having mine for 5 months or so, and paying careful attention to how the motor behaves under various conditions, I’ve come to this conclusion. The 2.73 certainly may yield better MPG’s under the most ideal circumstances. But that is the catch. …The margin of opportunity for when it truly is more efficient is really slim. Why, because it’s so far out of the power band, that the moment you ask it to do just a tiny bit more (1% grade, slight acceleration, or slightly faster), it really struggles. Real world driving certainly isn’t a loops around the Bristol track at 50mph.

For instance, at 65, the 2.73 in 6th is only doing 1532 RPM. If it is perfectly flat, and there is no need to change speed for any reason at all, yeah, it will yield really good results. The problem is that its so far out of it’s powerband that one may have an opportunity to lug it, and not really even knowing it. You’re pushing more gas in the motor, but you just aren’t seeing the results, but it’s so easy to do because you don’t feel the response. The 3.31 at 65mph is running at 1858. Now, since it’s running higher RPMs under perfect conditions, yeah, it would be easy to conclude that it would be using more gas. But I believe that there is a greater margin for opportunity of good mpgs with a 3.31 under real world driving.

Also remember that gearing is linear. Wind resistance for all practical purposes is exponential. A 10mph increase (from 65mph to 75mph) is just a little over 200rpm’s more in 6th on a 2.73. It’s the same RPM increase as if you went from 55mph to 65mph, but the wind resistance has gone up a huge amount (proportional to your car’s drag coefficient). So the moral of the story is speed kills your mpg’s regardless, and if you really want to see those number be great. Keep the speed down. Hogasswild has posted some great results - his being a 3.31, but I believe he’s mentioned that he’s pretty good about keeping his speed in check.

For what its worth, my commute is 40 miles round trip. 20 miles on 70mph hilly interstate, 12 miles on 60mph interstate, and the remainder on side streets. I’m getting about 27 to 28mpgs. Now, when I get the 3.31 installed and it doesn’t match up with what I’m saying, then you can disregard every single word I’ve said. :-)

 

Just about what I get with a 2.73 and a tweaked 87s Bama tune that I love. Think I can do better with the stock tune but not as much fun to drive.

 

You guys are getting great mileage . I average 20-21 MPG mostly city. In the very few opportunities when I got to spend more time on the highway than in city, I got around 24-25 MPG.

I guess I need to take it for a 400+ miles highway trip and be careful with the foot - to make sure it can get to 30 MPG ...