Im gettin about 180 mp tank mostly hwy miles. But I have alot of mods and have a heavy foot. I can get 220 if I go easy on it. I used to get about 250 before most of my mods on the hwy and about 200 in the city with a heavy foot. So now im doin about 17 mpg hwy. Which is really bad, around 12 city.

 

As far as gears go, when i had the stock 3.23s i got about 300+ miles a tank. Now I have the 4.10s and I get a little over 200 miles a tank. Ouch.

 

I keep my tires inflated to 33 psi and get about 15 mpg. When my tire pressure goes to 31psi my mpg drops to 13 mpg. So keep your tires properly inflated, it makes a big difference in gas mileage.

 

2002 Z28 M6

Descreened maf
Free ram air
K&N
Otherwise stock

I went on a road trip (luggage and all, running the defroster), set the cruise at 80 mph and when I filled up I showed 27.65 mpg. This even involved some 7% grades in the mountians. I've also made the same trip after doing 80 miles in the city (I average 20 mpg in Columbus traffic) and filled up somewhere over 300 miles on the trip odometer (again, cruise at 80 mph). My M6 gets nearly the same mileage as our Mazda Protege 5 (with 135 hp and a 5 speed). You know which one I take on trips.....