why do pickup truck manufacturers engineer their engines’ peak power so high in the rpm range?

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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

6 Answers

Anonymous 0 Comments

> 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

No. peak power is used mostly when you are accelerating. Cursing at speed should not use peak power, accelerating to speed uses much more power than maintaining speed does.

Making the truck go from 50-60 mph takes more power than maintaining speed at 60mph does.

Also there’s the issue of hills to contend with. If highway cursing on flat ground required peak power, what would you do if you encountered a hill? Slowly lose speed?

Anonymous 0 Comments

Well you don’t particularly care what the RPM is for peak power, it can be fixed in the transmission. Also, peak power is always going to be at a high RPM, as higher RPM means more cylinder worth of fuel/air mixture per second. You expect power to basically go up with RPM until you hit the peak RPM.

Second, you don’t want to tow at peak RPM, you want to tow at peak efficency at the required power. That’s usually a lower RPM, and that’s usually how the transmission is optimized. If you need peak power (for a hill or whatever) you downshift to get that.

Anonymous 0 Comments

Nah. When a vehicle needs maximum power will not be when it needs efficiency. If a truck’s power band is at 2,000 rpm then it is not going to have much actual power in that power band. Sure, it will be efficient while running at max power, but why would you want to be running max power when cruising on the interstate? You need power most when accelerating.

Power bands will naturally be at higher RPMs due to the physics of engines – power is RPM times torque. Thus, as revs go up, so does power until torque begins to drop.

Anonymous 0 Comments

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.

Anonymous 0 Comments

HP vs Torque. HP is how hard you hit the wall, Torque is how far you take the wall with you.

Anonymous 0 Comments

Im just used to getting 12+mpg while towing 6000 lbs with a diesel. It hurts to think of getting 8 mpg while towing 4000 lbs with a gas truck. Even though after doing my math, for my purposes, cost of ownership and operation of a gas truck will end up being cheaper overall. I know gas engines just arent capable of the efficiency under load at the low rpms that diesel engines are, but it makes sense to me to emulate diesel power curves as much as possible in order to emulate diesel fuel efficiency as much as possible.