How to Become a Hypermiler

Step 9 Acceleration

The best way to accelerate is by keeping your engine at peak torque. This means, accelerating too slow (as you may have been told to do) and accelerating too fast (bringing your rpms up high) are inefficient and will reduce your fuel economy numbers.

Ideally, peak torque at 50-75% throttle.

Comments

[jimmytvf]

that's what i'm talking about, playing with throttle and RPM. Low rpm = low fuel --> FALSE Low rpm make the time lapse between injections increase, so we get less fuel in a second, that's true, but, if we have to step more the throttle to get the same rpm, the volume of fuel increase, and the car needs energy to move and spend more fuel. you have to play with what your engine needs and, at the same time, manage the efficiency of the fuel you send to the engine

[jimmytvf]

best rpm shiftings on petrol: 2000 to 2500 RPM
best rpm shiftings on diesel: 1500 to 2000 RPM (lower rpm torque point)

[trebuchet03]

To your earlier comment - this is why instantaneous fuel economy data is important ;)

Yes, we care about long term average consumption - but you won't get good long term averages if you can't keep your instant consumption low (as you accurately said: "play with what your engine needs").

[jimmytvf]

yes, i've just realize about that ;)

[horta_12]

I read many artikles on this topic that stated you should accelerate slowly; so I did. I was accelerating with my RPMs below 2k and usually lower. It only took me two commutes to notice my fuel gauge drop significantly faster than it should have been. It was actually dropping faster than when I was driving aggressively. Basically, I'm just verifying with my own experimentation that there is a happy medium between accelerating too fast and too slow. I would say a broad estimate for most cars these days would be about 2k to 2.5k RPMs. Thank you for the good information.

[Outlander]

This is a very old step, since cars have been around. It's called the "power band" Basicly going below the power band is called "lugging" the engine and going over the power band is just wasting fuel. If your car develops near peak torque at say 2,500 RPM, always accelerate near that RPM. If one is lugging the engine(accelerating below the engines power band), then it is just wasting gas as the engine struggles to accelerate. The only time when going below the power band will save on gas is during highway cruising when all the throttle one needs is done by "pulsing" to keep the car at a certain speed. Basicly pulse the throttle+ low RPM + near constant velocity will save on gas.

[crestind]

Can you explain why 50% would be best? I usually accelerate slow enough so the needle doesn't go up and shoot back down (don't know what that's called...)

[trebuchet03]

50% will keep the engine in closed loop and keep manifold vacuum low. Vacuum reduces efficiency in the form of pumping losses. Diesels naturally run around 0psi (whereas gassers will idle at around 22 inches of mercury).