Is More Horsepower Always Better?

A number of drivers and owners have said that Toyota engines have more horsepower.

“I think everybody in the garage is down on horsepower compared to what the Toyotas are.” Kevin Harvick

One report of dyno tests after the 150’s at Daytona last February said that the #20 had at least a 15 horsepower edge at his rear wheels over Chevy’s #88-Dale Earnhardt Jr. and 30 horsepower more than Chevy’s Kevin Harvick. NASCAR retorted that, out of the 10 different engines tested after the Gatorade Duel 150 qualifying races, most of the engines tested varied by less than 10 horsepower, with all but two of the engines within 7-8 horsepower of each other. (What I consider a very reliable source reported that the 30 hp number was because one of the tested cars had a valvetrain problem.)

In reality, the numbers the public generally gets out of these tests really don’t matter. One reason Cup engines generate high horsepower is their speed: 6500-9500 rpm at a plate track. The faster an engine runs, the faster it converts the chemical energy stored in gasoline to motion. Power measures how fast energy is produced. Higher horsepower means that you’re getting the energy out of the gasoline faster. So the engine that has the most horsepower ought to be the best, right?

Horsepower depends on (among other things) engine speed, as the graph below shows. When an engine runs at low speed, less gasoline is combusted each minute and less horsepower produced. As the engine runs faster, more gasoline combusts each minute and more horsepower is produced. When you hear someone talking about ‘the horsepower’ of an engine, they usually mean the maximum (a.k.a. peak) horsepower. So does the engine with higher peak horsepower have an advantage over an engine with lower peak horsepower?

Not necessarily. Car 1 in the drawing below has higher peak horsepower, but it doesn’t reach that peak until near 8700 rpm. At most tracks, the engine will spend much more time operating in the 6500-8000 rpm range (where the engines are running from the middle of the corner off). In that case, even though Car 1 has a higher peak horsepower, Car 2 will have the advantage over the lower rpm range. The point of this is that you can’t characterize an engine with a single number like peak horsepower.

Dr. Andy Randolph, Engine Technical Director at Earnhardt Childress Racing, was kind enough to answer my questions on this topic–some of which you’ll read about in the next installment–but he said something that I found really insightful (not to mention amusing).

“Power gives you speed. Torque makes you feel good”

To put that in physics terms, power is proportional to speed while torque is proporational to acceleration. When you step on the gas and you start accelerating quickly, that’s torque you’re feeling. At the start of this season, Toyota (yes, the manufacturer with the ‘horsepower advantage’) was struggling to get low-end torque (which means torque at low speeds). Their drivers were having problems getting onto the throttle as they come off the corner.

I drew two curves in the first picture: horsepower and torque. Torque is like force, but it’s a turning type of force. The steeper and broader the torque curve, the more the car will be able to accelerate. If there’s only one line on a track, you may want your peak horsepower at a high speed, so that you can go fast at the end of the straightaway, get ahead of other cars and claim that line. A car that can accelerate off the turns may have an advantage when passing.

Andy said, “There’s two ways to be fast: There’s fast on the clock, like when you qualify, and there’s fast during the race.” Having one doesn’t necessarily imply you have the other. On a plate track, a typical engine might have peak power around 7600-7800 rpm. The problem is that you spend most of a race like Daytona running around 8500-8600 rpm. If you lose 15-20 hp between 7800 and 8500 rpm, do you really have an advantage?

We like to have ‘a number’ to quantify things (e.g. standardized testing), but as anyone who’s pulled a B in a class by getting all A’s and then blowing the final, a single number rarely tells the whole story. Peak horsepower gives the engine guys something to brag about, but it doesn’t tell you whether one manufacturer has a meaningful advantage over another.

Next installment, we’ll dive into comments from a couple of drivers who think their manufacturer’s (Dodge and Chevy) engines are at a disadvantage at plate tracks and see if science substantiates their claims.