It sounds like this“The car with the higher horsepower figure is the quicker car.”
Thinking the car with the bigger peak number is the quicker car
Why it feels right
A single number is easy to compare and to print on a badge. 300 hp beats 250 hp the way 300 dollars beats 250 dollars. Adverts quote one figure, magazines rank cars by it, and the figure really does correlate with how fast a car can ultimately go. It is natural to treat it as the whole story.
Why it’s wrong
A peak is one point on a curve. One engine may reach its peak only at 8,000 rpm and be weak below that, while another makes nearly its peak from 2,500 rpm up. In ordinary driving, where you rarely rev high, the second can feel stronger and be quicker.
A worked example
An engine's power changes with its speed. Picture two cars. Car A has a small, high-revving engine: 300 hp at 8,000 rpm, but only 100 hp at 3,000 rpm. Car B has a turbocharged engine: 250 hp, available from 3,000 rpm all the way to 6,000 rpm.
On a track where a driver keeps A above 6,000 rpm, A wins. But pull out to overtake at 3,000 rpm, or drive up a hill in a high gear, and B has about 250 hp where A has 100. B accelerates harder at everyday revs, and doesn't need a gear change to get there.
The peak figure says what an engine does at its best moment. What you feel depends on where you are on the curve. A fairer comparison is the whole power curve over the speeds you use, or the car's measured acceleration, such as 50 to 80 km/h in a high gear.
The same thing explains why two cars with the same horsepower can feel quite different, and why a car with less peak power can be quicker from 30 to 70 mph.
How to catch yourself
- You rank cars by their headline horsepower figure alone.
- You don't look at the revs at which the peak occurs.
- You think a 10% higher peak means a 10% quicker car in daily use.
What to hold instead
A peak figure is one point on a curve. What matters is how much power the engine makes across the speeds you actually drive at. An engine with a flat, wide curve can feel and be quicker in everyday driving than one with a higher peak at high revs.
Where you’ll meet it
- Choosing between a turbo and a naturally aspirated engine.
- Comparing a diesel and a petrol version of the same car.
- Reading a dynamometer chart instead of a brochure.
Questions people ask
- Is a higher horsepower figure always faster?
- Not always. It describes the single best point of the engine's power curve. In everyday driving, how much power is available at ordinary revs matters more, and so do weight, gearing and traction.
- Why do turbo engines feel quicker than their power suggests?
- A turbocharger lets an engine make strong torque at low revs, so the power is available early and across a wide range. In normal driving you use the middle of the rev range, so the car feels strong without having to be revved hard.