Area Under the Curve

Harold Bettes: People like to argue over torque and horsepower, but in the process they often overlook the area under the curve. That refers to the average horsepower an engine produces throughout its operating range. Let’s say one engine produces a power curve that looks like a church steeple, while another engine has a power curve shaped like the top of a balloon. Even if both engines produce the same peak power, the engine with the broader curve will be both more fun to drive and substantially faster at the track. That’s because when you shift gears, the engine with the balloon-shaped torque curve will be making more horsepower. For this reason, the area under the curve, or average horsepower, is a much more effective way of gauging how well an engine will perform than peak torque or horsepower.

Scott Shafiroff: People want to see a big peak horsepower number, but average horsepower is much more important. It’s not just the peak number that counts, but rather the horsepower that’s produced over an engine’s rpm range. Some people think that building street motors is easier than building race motors, but that’s not always the case. In some ways it’s harder to build a street motor since they have to operate in a broad rpm range. Whether it’s a street motor or a race motor, the goal is to maximize the average horsepower output.

Low End vs. Top End

Judson Massingill: In America, we tend to look at low-rpm engine output in units of torque and high-rpm output in units of horsepower. However, the truth of the matter is that you can’t separate the two since horsepower is a derivative of torque that’s mathematically calculated from torque and rpm. People are familiar with the formula horsepower equals torque times rpm divided by 5,252. So if you have more torque at, say, 5,000 rpm, than the guy in the other lane, you’ll have more horsepower as well. Likewise, if an engine is producing lots of torque at 3,000 rpm, it’s also producing lots of horsepower at 3,000 rpm. Another way to look at it is that if you’re building an engine to maximize torque output at low rpm, you’re also building an engine that makes lots of horsepower at low rpm. People tend to get very passionate about the horsepower versus torque topic, and some people are torque guys while others are horsepower guys. I’ve been at engine conferences where people got so riled up about this debate that they had to be escorted out of the room by security. The funny thing is that they’re arguing about the same thing. CHP

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