I got 30MPG/70+MPH on my last bullrun (1200mi in 17+ hrs, almost all highway) ... 87 octane (stock) tune, CAI, 25% underdrive crank pulley, 245/45/17s.
In town, however, I get around 16MPG (stop & go suxs @ss).

 

NOOO!!! That is essentially the max amount of pressure the tire can hold before things become unsafe (e.g. tire goes boom if you hit a curb). If you inflate it too much, the center of the tire will wear out quicker. The owners manual suggests 35 for optimal handling and wear for everyday driving. Just make sure you check your pressures after the car has been in the shade and cool for a few hours - the best time would be in the morning.

 

guys, please remember that the tire psi is gonna be different on the size tire you run. the lower the profile, the higher the psi, usually. the brand of the tire, etc, will all make a diff. so there is not necessarily a "correct" pressure for all mustangs.

 

how can i find the psi for optimal longevity, fuel efficiency and performance? i tried to google my tires and specs but couldn't find crap!

 

ignition stuff.... New spark plugs, wires, etc (if old)

 

you get more than i do city is 18 and hwy is 20.. i dont understand why my mpg suck so badly!!!

 

Damn, that's horrible, I get better than that. Check your spark plugs, wires, fuel filter, tire pressure, coild pack, all can have a drastic effect on mpg.

 

I'm getting about 18 mpg now as well. It's weird how much difference there is from car to car with the 3.8. Even in tip top shape and driving like grandma behind the wheel I've never seen better than 21.

 

well i just did the sparks last year and i was told no major tune up until 100k.. i am at 72k now.. i can lighten the car.. take the spare out..

 

My v6 gets horrible mpg, i get MAYBE 200 miles out of a tank. Only 30,000 miles on her, so i dunno. Iv always just kinda excepted it as a mustang thing