Hey y'all,

I got to thinkin' about this hear subject this hear mornin' as I wuz drivin' to work. If it were true, that spirited acceleration was more fuel efficient than slower acceleration due to the opening of the throttle plate / pumping losses yada yada yada ... wouldn't it be more fuel efficient to be pulling a slight grade with a gasser than to drive on level ground?

Say like on an interstate where you're already having to overcome wind resistance, and then you add a slight to moderate grade to the picture. I mean, the throttle plate would be open more on the grade. Reducing the pumping losses, shouldn't the fuel mileage increase according this throttle plate theory? It seems like the same situation to me.

1. Accelerating requires a lot of load on the engine, especially accelerating briskly, and opens the throttle plate more, reduces pumping losses which leads to less fuel consumption, - OR -

2. Climbing a slight grade on the interstate (for example) which requires a lot of load on the engine, and opens the throttle plate more, and reduces pumping losses which leads to less fuel consumption.


However, I know climbing a grade will require more fuel than traversing level ground. So now (in my mind) I'm back to slow and steady accelerating would use less fuel than briskly. Unless someone can explain to me how my analogy (hill vs. brisk acceleration) *may* be wrong.


Shooooot. I just got to thinking about this even more. If this throttle plate theory were correct, then on the interstate up and down hills continuously would be more efficient than level ground. Up would be a more open throttle plate and down the other side would be coasting. Best of both worlds. But from my experience, I've always gotten better fuel mileage on level grounds.

- JyRO

 

This has been blown slightly out of proportion. My original question was more along the lines of accelerate slowly for a longer period of time versus accelerate quicker for a much shorter timespan.

It went way off in left field from there.

 

HotRod - I don't think it's been blown out so much. I think your question is a great question. But the actual answer is not just 'yes' or 'no.' I think this throttle plate thing has a strong bearing on 'the answer.' Just not sure if I quite agree with the throttle plate thing.

Now just sit back, loosen you belt, and get ready to feast on all these delicious opinions. That's one of the reasons I really enjoy these forums. Differing opinions. It shows me how tunnel-visioned I am, and how I might could see something from someone else's point of view.

But if you prefer just a short answer, my opinion is the right one. Just go with that!

 

The pumping losses would be less when climbing a grade, but the horsepower requirements are greater; this more than offsets the pumping loss reduction. To confuse the issue, the BSFC would probably be better climbing the grade (the gasser is operating closer to its peak torque, which is generally the best BSFC point), but the MPG would be less because more horsepower is being produced.

Rusty

 

Rusty - I agree. And this is what confuses me. Brisk acceleration requires more horsepower, the same as climbing a grade. I'm stuck. No disrespect at all. But I still think slow acceleration is more fuel efficient than brisk.

And thanks for the explanation about the pumping losses, you explained that very well for me.

- Jason

 

With a diesel, since it has no throttle plate, you may well be right. I haven't tried to quantify it either way.

Rusty