Thread: Hard right foot

i wouldn't know mines always at full revs

"What better way to see this great land of ours than flat chat!"
Russell Coight

It probably depends on what you mean by "efficient". Assuming you mean "fuel efficient", and assuming you want to end up with the same overall journey times, it will depend to some extent on what engine you have. However, it makes very little difference to turbocharged diesels, and not much more to modern NA diesels in good shape. What you need to do is look at the specific fuel consumption curves - for most diesels (especially turbos) they are pretty flat, except right at the top and bottom of the usable rev range.
Although not the question you asked, best fuel efficiency is gained by driving so as to avoid using brakes - i.e. look ahead and plan to slow as necessary simply by easing off on the throttle rather than usingbrakes, and accelerate slowly - but this can be done at a wide range of engine revs, although probably easier if you keep the revs down.

If by "efficient" you include maintenance as well, engine wear will generally be reduced if operated at the minimum engine speed consistent with the required speed.

On the other hand, petrol engines usually have a much more peaky curve for both engine speed and specific fuel efficiency. As a general rule, best fuel efficiency will usually be by keeping the engine rpm close to the peak torque rpm.