Im in the market for a full size gasoline pickup for towing and hauling. Doing ALOT of homework, and most of the different truck brands have power bands at around 4000 rpm. (Lowest was ecoboost @3500) That seems awful high? Wouldnt you want to engineer the power band closer to 2500-3000 rpm where most tow rigs cruise at highway speeds for the sake of fuel efficiency?
In: Engineering
It takes significantly less power to cruise than to accelerate. That means that cruising at max output is a waste of energy and, therefore, fuel. Instead, you want to rev as low as possible (without lugging or stalling), only climbing to higher outputs when actually needed (to climb hills or accelerate).
This is the same regardless of where your peak power occurs. For example, an average-ish tractor trailer generates peak output at about 1000-1300 rpm. However, they often cruise (on flat ground) at a *blistering* speed of maybe 700 rpm.
Big, low revving engines also have another issue; teeny tiny power bands. If the engine in my example gets below 500 rpm or much above 1800rpm, it’s basically useless. Big trucks get around this by having a lot of closely spaced gears – sometimes 20+ for heavy haulers, but lighter ones usually have 10-13.
The engine in a pickup (or a car) has a much wider power band, which means there’s a lot more wiggle room for gearing. You can haul a pretty good load with only a few gears – my old F150 has a 4-speed, and 5-6 speed manuals were normal for a long time. Some newer trucks have a 10 speed to make them drive smoother and optimize engine efficiency (for power or fuel), but it’s not really necessary in most cases.
TL:DR the rpm of your peak power is mostly irrelevant to your fuel economy at cruise. It’s just a “run engine here on hills/acceleration” indicator.
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