The fuel economy tips in the carbking's excellent link need to followed by all of us. However, there was one that may need a little discussion: "Adjust your driving habits. Everyone knows that full throttle acceleration wastes fuel, so we will not discuss this." Let us disscuss it.
Full throttle acceleration may actually save fuel. A few years ago (to someone my age 1985 is just a few years ago) Car and Driver reported on some road tests conducted by BMW that fairly convincingly showed that full throttle acceleration could increase mpg over a simulated city driving scenario by somewhere between 10 to 25 percent. As I recall (I seem to have misfiled the article) BMW measured about 20 mpg with full throttle acceleration from zero to about 30 mph and about 16 mpg with quarter throttle acceleration. With either throttle setting, better MPG was obtained by shifting at 2000 rpm than at 4500 rpm. This is also one of the reasons why better mpg can be obtained with a manual transmission, as the driver can independently control both the throttle and the transmission gear selection. Some automatics do allow the driver to control the shift points. Otherwise, full throttle acceleration results in lots of rpm and pumping losses.
The first article where I read about the advantage of full throttle acceleration was in Motor Trend, June 1956. In this report, they averaged about 20 mpg at an average of 30 mph average trip following the recommended “drive like an egg is between your foot and the pedal”. Then, they used the “burn and coast” technique, where they accelerated at full throttle, in high gear, up to about 40 mph, and then coasted, in neutral with the engine off, down to about 10 mph, restarted the engine by popping the clutch in high gear, and repeating the cycle as required to get to the end of course. This resulted in 42 mpg. Admittedly, this might be tricky in heavy traffic, as all of the drivers would need to get their burns and coasts in phase to from having a few bumper touches. I’ve been told that this burn and coast technique has been used in the super-economy trials where several hundred mpg is achieved.
This may seem to be counter-intuitive, but if one works through the physics (engine efficiency vs. rpm and manifold pressure, F=ma, V= at, D=CdqS, E=mv^2/2 etc.) of the acceleration and steady speed of a car it will become apparent. I convinced my son to try a modified version of the burn and coast technique driving between St. Louis and his school in Springfield MO in his S-10, with an inline four. On one leg he measured 34 mpg compared to the 27 mpg with a normal steady speed, averaging about 65 mph both methods, driving the same direction.
I’ve been looking for a controlled test that shows that part throttle is better than full throttle for mpg, but I cannot find one. Of course, if you engine has so much torque that it smokes the tires at or near full throttle, you may need to back off or get a taller gear. That is real secret – drive at nearly full throttle with the rpm in the range for near-peak torque. This requires a multi-speed (or CVT) with a very wide range of ratios.
