Why do identical motors have different power ratings?

Hi,

I've noticed that models of the same make but in different categories have engines of the same size with the same number of cylinders (for example, a 2-liter in-line 4-cylinder), but different power ratings.

How can this be explained?

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Hello Philippe,

The number of cylinders and the displacement of an engine are not enough to explain a difference in power. First, you need to consider whether the engine is naturally-aspirated or supercharged. When an engine is supercharged by a supercharger or turbocharger, power and torque are higher. Yet displacement remains the same.

Taking your 2-liter 4-cylinder example, the base Hyundai Elantra comes with a naturally aspirated 2-liter inline-4. Power output is 147 hp and torque 132 lp-ft. The same Hyundai Elantra, but in a sporty N version, is also equipped with a 2-liter 4-cylinder. But it's turbocharged, and the specification sheet lists 286 hp and 289 lb-ft.

On the other hand, when designing an engine, engineers always have to make choices. The development of a powertrain responds to specific needs, and compromises have to be made.

If a manufacturer develops an economical car or a radical sports car, the engine will obviously not be designed in the same way. In an economy car, engineers will focus on low-end torque and keeping fuel consumption as low as possible. For a sports car, engine designers will be able to use higher-performance parts and more technology, to rev the engine higher and thus gain power and torque.

This can be seen at Volkswagen, which uses a turbocharged 2-litre 4-cylinder in several models, but whose power varies significantly:

Volkswagen Tiguan : 184 hp/221 lb-ft
Volkswagen Golf GTI : 241 hp/273 lb-ft
Volkswagen Golf R : 315 hp/295 lb-ft (with DSG gearbox)

This example clearly illustrates the choices made by Volkswagen. The Tiguan's engine was developed with rationality and pragmatism in mind, while the Golf R's engine was pushed to the limit, to give its driver a thrill.