How to keep the motor at its most efficient RPM?

[Trailer-man]

Just took out the trailer for the first time this year, and managed to do something different! While coasting along at about 80 kph, I managed to get the engine down to about 2000 RPMs - and could even slowly up the speed to almost 90 at times, on a level grade.

I am pulling a travel trailer (wind resistance) with a loaded weight of just under the 3500 lbs.

Now, here's the question. How can I effectively find that 'sweet spot" with the engine to be able to get this. In the past, I have sometimes been able to get to around there, and sometimes not. So the RPM (hence gas consuption) goes from 3400 at times, to at best before this at about 2700. But I can never quite fiugure out how to get that unrev'd situation.

Any ideas would be appreciated - as it is not too safe to be travelling down the road, easing off on the accelerator trying to get the engine into a lower rev state. If I could hook into the 2000 revs all the time, it would be really great - but I know that just normal driving without the trailer is often at about 2600.

Thanks - assistance would be appreciated (having a trailer these days is not too cool!).

[Max]

Simply put...the lowest RPM range that will effectively provide you with adequate power without having to bury the pedal (lug) the engine down (i.e. the least amount of throttle).

You need a dash mounted engine vacuum gauge. The higher you keep the vac reading the better mileage / efficiency you'll achieve.

Personally? I think you're trying to over engineer a situation that will give little or no pay back in return. Just drive it conservatively, keep it tuned to the max, then what you get is what you get.

[Trailer-man]

Perhaps ..
But I had never found this one spot before .. and it sure made a difference in fuel efficiency ..
Just did a "full-tank" calculation, for the full trip out, back and without the trailer in city for a short while, and the result is: 13.337 l/100km - which is the best I've ever done in city-only, no trailer. I was quite amazed, since it has been up to 18.5 l/100km at times if I don't pay attention to kicking it down.

I guess another way to state the issue is: if I just "accelerate and drive", as one would normally without a trialer, and pay no attention to the engine reving sounds/feel, then I will burn a lot more gas than if I release the accelerator occasionally as I try to get to a low-rev cruising speed ..