Accelerating and gas mileage talk

[Chris]

So I’ve had this question for a while and no one seems to know the exact technical or correct answer.

If you accelerate from a stop 2 different ways, slowly up to the minimum shift RPM, up through the gears normally to reach cruising speed (speed limit), which in Canada is 50 km/h.
Alternate way is to accelerate as fast as possible only up TO the minimum shift RPM (same as accelerating normally or “slowly”) and getting up to cruising speed much quicker, but not going above the regular RPM’s.

Do they both use the same amount of fuel? If not, why would the faster acceleration use more fuel if the RPM’s match exactly? Question applies mainly to automatics and for the same exact car in both cases, but would like to know for manual as well.

I get quite a few different answers or “theories” but would like to know which one is accurate.

Topic

[Mike]

This is difficult one to give an exact answer to.

It’s a question of burning less fuel per unit of time, but burning it for more units of time, as opposed to burning more fuel per unit of time, but burning it for fewer units of time. From a pure physics equation point of view, the end result should be pretty close to the same for both scenarios.

Back in the day of carburetors, a heavy foot always burned more gas. These days, with digital fuel injection, I don’t think there’s much to recommend either acceleration curve, in terms of everyday driving habits.

[Zac Aleksovski]

The engine doesn’t know if it has a carb or EFI. Step hard into the throttle & go into enrichment be it by longer injector pulse width or more fuel from running on the main jets, accel pump output & power enrichment. Didn’t those Myth Buster guys do a few MPG tests like AC on vs. windows open or the tailgate up or down debate on pick-ups? I’ve read an article about the super MPG Prius guys they accelerate super slow until they reach cruising speed. (54.5 MPH… in the fast lane).

[Chris]

Ya it is definitely a bit difficult to answer, but I agree more with oldskll about the enrichment. Also the more I think about it, hitting the throttle farther opens up the throttle body more and by default opens things up, fuel pump kicks up and injectors spray more fuel which in turn uses more gas for the faster acceleration. EVEN though you aren’t going any faster or at a higher RPM, it technically should use more gas to get there quicker.

BUT, at the same time, accelerating slower does take more time, keeping the RPM’s at a higher rate for longer which in turn should use more fuel in the long run?

Ya the mythbuster guys did the A/C myth tests, but this is such a close comparison with little to no variables, other than different ways to accelerate.

I’m guessing it doesn’t make too much of a difference, just a burning scenario that i’ve always been curious about.
I guess a bunch of math and an engineer would have to be involved haha.

Thanks for the input guys!

[Author]

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