What is the conversion formula between rated power and maximum net power?

[Hayley]

The formula is Power (W) = Torque (Nm) × Speed (rpm). Here is relevant information: 1. Definition: Maximum net power refers to the effective power output measured from the engine's power output shaft. The engine is equipped with all accessories under actual operating conditions and operates at the speed specified by the manufacturer on the engine test bench. 2. Operating Conditions: The engine is equipped with all accessories under actual operating conditions and operates at the speed specified by the manufacturer on the engine test bench. The measured effective power output from the engine's power output shaft.

[Tanner]

I've actually researched this. The rated power is the number printed on the engine nameplate, while the maximum net power is the actual usable horsepower when driving. Strictly speaking, there's no fixed conversion formula because each vehicle's engine bay losses vary. I estimate it's roughly around 90% of the rated power, since the engine needs to power components like the alternator and air conditioning. For example, a car with 150 horsepower rated power would realistically deliver about 135 horsepower at the wheels. Measuring this requires removing all accessories and testing on a professional dynamometer, but for regular people, referring to the manufacturer's published net power figures gives a more reliable indication of actual performance.

[MacLincoln]

In principle, the rated power is the peak data measured by the manufacturer under ideal conditions. However, when the car is on the road, the engine also needs to allocate power to accessories like the generator and cooling pump, resulting in a consumption of about 15%-20%. I often review test reports, and the common conversion method is to estimate the maximum net power by multiplying the rated power by a coefficient of 0.85. For example, a 2.0T engine rated at 200 horsepower often delivers around 170 horsepower at the wheels. However, the transmission efficiency also affects the final performance, a point many people tend to overlook.

[DiPresley]

These two concepts are easily confused. Rated power is like the label value given by the manufacturer to the engine, while maximum net power is the horsepower you can actually use. There is no conversion formula at all—it all depends on actual test data. From my own research, I found that the same engine can have different net power in different models. For example, some luxury cars use lightweight accessories, reducing power loss to around 12%. For ordinary family cars, the loss is typically about 18%. If you want to save fuel, focus on cars with higher net power, as their power conversion efficiency is better.