Some of you guys just drive your cars hard, or set the cruise too high. You'd be really surprised at what you can pull out of your car if you take the time and do it right.
I've pulled 22 mpg out of a 4-hr trip from GA to FL in my 760rwhp 9-sec foxbody, 23mpg out of my mother's Ford Excursion on a 600 mile trip from FL to OH, and 38mpg out of a 1997 Chevy Corvette on the route as the excursion. Keys to fuel mileage:
- 35psi in the tires (some push it higher, but I have seen tires wear in the center from over pressure, and there are other negatives to noise/vibration/harshness in going to a pressure that's too high. While you might achieve higher mileage, you should ask yourself if the trade-off is really worth it)
- Set the a/c system's compressor off, and just run the fans with the windows up if you can find a way to be comfortable
- Find the sweet spot speed for your vehicle. My vette's, for example, is 45-55 mph. With anything over 60, I really see the mileage drop off. Air resistance always becomes a significant factor at speeds over that as drag increases exponentially with velocity
- Don't run the cruise - a sensitive foot will do a better job of modulating the throttle. The goal is to use the motor to always apply a positive force to maintain or accelerate the vehicle. Pull it out of gear if the vehicle will maintain speed on its own.
- Coast - when a down hill allows you to maintain or increase vehicle speed without throttle, take advantage of it. Rev-match when you go back into gear to lessen the work of your clutch and synchros. This can make a big difference on hilly portions of the interstate like those in TN and KY.
- Use deceleration fuel cut-off (DFCO) only when there is a reason to regulate vehicle speed (legal or hazard such as preventing high speeds on twisty mountain roads).
- Same goes even more so with brakes - use sparingly, and coast or use DFCO when able. Try to anticipate upcoming turns and corners so you don't have to use them and can coast to the appropriate speed.
- Accelerate moderately, not easily - getting to your final drive gear relatively quickly is far better than slowly accelerating and staying in the earlier gears for longer. Don't take this to extreme and accelerate too fast. When you accelerate aggressively, your EFI system considerably richens the fuel mixture to prevent detonation, and hence wastes fuel.
- reduce electrical draw - anything that pulls electricity increases the alternator's load and hence the load on the motor. This can be relatively insignificant for things like listening to the radio, but if you're running a large system, your high beams, a couple of TVs, etc... you'll notice a difference in mileage if you're measuring.
These guys pulling low 20s out of their Mustang GTs aren't trying too hard. I live in a hilly area in Germany where I drive up and down twisty, hilly roads every day to work and back and still average a bit over 24 mpg in the Corvette and closer to 30 mpg in my 4cyl BMW. People think it takes driving like a grandma to pull good mileage, but I find it more challenging, and interesting to focus on efficient driving techniques. You do end up taking a turns and curves at higher speeds than you otherwise would. I love driving a car hard, too, but driving efficiently can be just as fun in its own way, and more rewarding financially (fuel, tickets, lower probability of accidents).