Feb 05

Fuel Mileage Primer : Part 3

Times are hard. Moneys tight. Today I’m going to show you how to operate your car for maximum gas mileage. You can own the most fuel efficient car on the planet, but if you’re not up to the task of drivng it well, you won’t be gaining anything. Like the Prius that just flew past you at 85.

The number one tip is to leave with plenty of time and just cruise. So now we know what the lowrider scene is good for. But not really. The best mileage is to get into your highest gear with the lowest usable RPM. Now I’m not talking idle RPM, but the lower end of the shift range. The idea is the high gear gains you the most distance per revolution. With you keeping the revs down, the fuel required is dramatically less. And that is the big key to fuel mileage. Keep the fuel needs down in all situations. In my own driving, and a very tight budget, I find myself taking the higway commute at 55 instead of the roads 65 limit. My current driving mantra is “If you wanna go faster, pass her.”

Another good tip is to pretend there is an egg between your foot and the throttle pedal. Large throttle movements make the engine lose vacuum. And that is your friend. Less vacuum means more fuel in to match the increased air coming in. To help you understand vacuum, when the throttle blade is closed or not fully open, the engine isn’t taking in full air. The lack of airflow creates a vacuum. For efficiency’s sake more vacuum means better mileage. For maximum power, not so much. To keep the vacuum up, you want to lead some throttle just before you climb a hill. And on the way down, keep it closed. There is no better help to your mileage than free kinectic energy. If you’re sure you’re not approaching a speed trap, a neutral coast and riding out the extra momentum will help much more. Speaking of momentum, keeping up the speed through the corners, keeping the car in higher gears, will gain you some miles as well. Of course I’m not talking about taking a 20 mph turn at 60, but I’ve personally gotten 27 mpg in my 5.0 Fox body with aggressive driving on the back roads using these tips.

Now comes the controversial part. There are two competing theories when pulling away from a stop. One side says that less throttle and slower is better due to the increased vacuum. The other is more throttle reduces the pumping losses and gets you to your cruise speed faster. And I have experience with both working. The speed density 5.0 Mustang liked heavy gas coupled with low revs and quick shifts. So far a mass air modular Cobra Mustang does better with high vacuum and the rest the same. I don’t really have a preference, just reporting my findings.

I’m sure I’m not the only one noticing the recent trend of turbocharging small engines in todays economy cars. With EcoBoost, Skyactive, ActiveE, and whatever catchphrase some company is coming up with to explain how their engine system is more efficient than everyone elses can do, basically they are putting a power adder on a small engine. Now in times past, power adders were worse on mileage. A normally aspirated engine runs on a 14.7 to 1 ratio air to fuel. On a power adder situation, the ratio should normally be a richer 12 to 1. And to be on the safe side, the manufacturers usually ran the engine with a richer mixture due to clean air regs. With todays direct injection controls allowing for finer tuning, the engines are much more efficient on fuel. Now with that said. Most of the previous methods are valid here as well. The main point is to keep the engine in vacuum or boost as low as you can. The same goes with superchargers. In fact, I’ve heard of a centrifugal package actually giving better mileage in hilly regions because the low one or two psi that it produces in daily rpm range actually increases the torque production. And more torque means less throttle added to pull a hill.

The last piece is routing your trip. The main thing is to keep the vehicle out of the lower gears as much as possible. Avoiding stop lights and signs is the key, but not that will take you way out of the way. Plan out your errands to make one loop instead of multiple little trips makes the tank last longer too. Nothing beats the mileage your car gets when its not running.

That pretty much wraps up the users end of the mileage puzzle. Any comments or tips you have to stretch out that fuel buck, drop us a comment.

Photos by:Tom Marshall