What fraction of peak horsepower do typical 4 door passenger vehicles use? I was surprised when I looked at the power rating of the engine used on a Humvee. It's only ~190 horsepower, which is exceeded by many sedan engines.
So an obvious question is why doesn't my Camry SE burn more gas than a Humvee and I think it's just because during regular use, it doesn't use anywhere near 250 HP.
Does anyone know about how much mechanical power a typical sedan engine puts out during highway driving?
Also, can someone speculate what the torque vs RPM graphs of a sedan engine and a Humvee engine look like and what the typical operating points are?
 A: Find a long straight hill, take your foot off the gas and see what terminal speed you reach.
From the rate of descent and the slope you can work out the power (in this case potential energy) required to maintain that speed.
For my typical modern aerodynamic small car I think it worked out at around 30-35HP to maintain typical highway (100kph) speeds.
edit: manual transmission and modern engine management system, so I'm assuming it wasn't actually burning any fuel
A: You might be interested in my answer to If an electric car were to drive without having to stop, would the range be greatly affected by the speed at which the vehicle is moving?. From just air resistance I calculated that at 70 mph the engine in my Ford Focus is generating about 17 bhp (12.5 kW).
Obviously you need to add in losses in the transmission. Apart from anything else the above result predicts a top speed of about 150 mph and I can assure you my Focus isn't that fast! This graph suggests that the rolling resistance is about 0.8 of the aerodynamic resistance at 70 mph, and that would make the total power about 30 bhp - reassuringly close to Martin's estimate.
A: At normal highway speeds of 75, or less, about 20 percent based how auto makers are gearing the transmissions in most cars.
