As much as you can possibly get, right? Well, that’s true in some situations, but it’s definitely not the case for every vocational truck or application. Over-powering could end up costing you money—not just a higher initial engine price, but also increased fuel costs. Under-powering can be expensive, too, if it prevents you from getting work done as fast as you want. And making corrections after your truck is delivered isn’t cheap, either.
Here are a few tips to help you determine exactly how much horsepower and torque you might need, right from the start.
The relationship between horsepower & torque
We use these words all the time to describe engine capability, but what do they really mean? In the simplest terms, torque is what gets you started moving, and horsepower is what keeps you moving.
If you’ve ever used a torque wrench, you know that torque measures the length of the wrench multiplied by how hard you can push it. If you apply 100 pounds of force to a two-foot-long wrench, that equals 200 ft-lbs of torque.
By comparison, horsepower measures how fast you can apply torque. Imagine being asked to maintain exactly 200 ft-lbs as you circle a bolt faster and faster. That quickly becomes a challenge, and engines face it, too. That’s why they produce peak torque at low RPMs—just what you need to get your truck moving. At higher RPMs, however, the focus quickly shifts to horsepower and how fast the engine can apply its torque.
Additionally, key loads like rolling resistance and wind loading (just to name a few) are also measured in horsepower—thus making it convenient for designers to predict the required horsepower rating for the engine.
3 applications that might require as much horsepower or torque as possible
Here are a couple common scenarios to illustrate when choosing the highest horsepower engine available may be in your best interest:
1. You’re not concerned about how much the engine weighs (higher horsepower engines typically weigh in at 1,000 pounds or more) OR how much it’s going to cost you (acquisition + fuel costs). If that’s your situation, then absolutely choose the most horsepower and torque possible. You’ll be able to get more work done faster.
2. Your application requires hauling heavy loads fairly long distances on the highway or interstate. Your truck is never off road, and you load and unload at docks in paved parking lots. On the highway, your truck travels at 75-80 miles per hour, encountering significant wind resistance (the effect can be as much as double your next biggest load). In that situation, a higher horsepower engine allows you to maintain the highway speeds you need to get where you’re going quickly. But you might consider a lower torque rating since startability isn’t as critical.
3. You’re in a heavy-haul application, loading and unloading large machines at jobsites located off road in gravel or dirt lots. Your loads can top 100,000 pounds and are very un-aerodynamic, with significant wind resistance. When traveling on the highway, you want to maintain relatively normal road speeds. In this case, you want to spec your truck with a high horsepower engine to help maintain good road speeds, as well as high torque to provide good startability from load sites.
Performance is about much more than horsepower & torque
Not in one of those situations? Then you want to think more carefully about matching horsepower and torque to your application—and that means selecting the engine AND driveline components that will work together to meet your expectations. After all, a high-horsepower/high-torque engine coupled with the wrong driveline won’t give you the performance you demand.
First, you need a good understanding of the conditions your truck will face. What kind of surfaces or slopes will you work on? How much rolling resistance or wind resistance will you encounter? Will you use the power take-off while moving? What about accessory loads on the engine?
Second, you need to know your performance requirements. How much load do you need to haul? How fast do you need to get work done? How much fuel are you comfortable using?
The answers to all these questions are critical when selecting engine size.
Predict performance before you order your truck
That’s a lot to consider. The good news is, truck manufacturers have some fantastic electronic tools to help you out. Just work with your dealer to input your parameters—horsepower, transmission, axle ratio, tire size—and one of these analysis programs will spit out a report that predicts how your truck will perform in a variety of conditions. These programs are remarkably accurate, and you can play around with the inputs until you achieve the level of performance you want—all before you ever place your truck order.
(A word of advice: If you have a truck that’s performing the way you want it to, spec a truck electronically with the same or similar engine and driveline components. Then run a performance report. Next, modify a couple parameters—change the transmission type or axle ratio, for example—and run a second report. That way, you can compare the two to see how the performance will differ. It’s simpler than starting from scratch and gives you a known baseline to work with.)
The bottom line: Horsepower and torque matter, but they’re just one piece of a much bigger puzzle when it comes to maximizing truck performance. Take advantage of the tools and experience your dealer offers to choose the engine rating and driveline components that are right for your application—the combination that lets you keep costs down and profits up.