Clint Sharp wrote:
In message , The Natural
Philosopher writes
I m not convinced that slow acceleration is as effective as its made
out to be.

Under heavy acceleration the engine management system will go open loop
and injects more fuel than is strictly necessary for very good reasons,
the excess fuel is burned in the cat and wasted so slow acceleration
will use less fuel even if the eventual speed is the same.


Yes, I know that, but the real point is where is the optimal throttle
setting for efficient acceleration. It ain't idle, and as you have
pointed out, it ain't full welly either.



the energy needed to get a car up to speed is the same.
Of course, but unfortunately real life internal combustion engines don't
run best with theoretical energy inputs so even though the amount of
energy required is the same you'll find that a heavy foot will still use
more fuel.

But a mouse foot may be just as bad. That's the point.

If what the engine is optimised for is top gear cruise at 56mph, thats
medium revs and maybe 1/3rd throttle.

Possibly that's where we should be accelerating?

I've been dong research. Its fascinating.
some facts seem to be well agreed.

1/. Full throttle is not efficient.It tends to cause over rich mixture.

2/. Max RPM is inefficient. It wastes power in engine friction.

3/. On other than racing engines, peak torque is arrived at at lower
than max revs. This is generally true even with a turbo, as the sort of
breathing or boosting that will make an engine develop peak torque at
peak RPM is totally intractable in a road car.

So that definitely means we want to not use full throttle or max RPM
when accelerating..

Down at the bottom end, it seems to be the case that wide throttle on a
very low RPM is not efficient either.

Surprisingly, this area of car engine performance seems ill understood
by almost all the sources I can find. Or its simply ignored.

Interestingly, one poster on a US group said that sub 50mh, he needed to
drop a gear to get his mpg back. Thats just cruising along.

I can't be sure, but I get the distinct impression that medium light
throttle and medium revs works best on my petrol machine, and in fact
the turbodiesel as well.