What is a naturally aspirated engine?

  • What is a naturally aspirated engine?
  • How does this differ from a turbocharged engine?
  • Parkers explains car tech terms

Naturally aspirated engines are those that do without turbochargers or superchargers, which means they breathe air at atmospheric pressure instead of using 'forced induction' to increase performance.

What do I need to know about naturally aspirated engines?

Traditionally, standard petrol engines have been naturally aspirated (also known as normally aspirated or even simply NA), while diesel engines have to come to make routine use of turbochargers to boost power and economy.

However, manufacturers are increasingly resorting to turbocharging petrol engines as well as diesels, as buyers continue to want both more power and greater fuel economy at the same time.

Turbocharged engines often perform better in official fuel economy tests, and they can provide a greater spread of performance from low to medium engine speeds upwards – meaning that you don’t have to work the engine as hard for the same acceleration.

What are the benefits of naturally aspirated engines?

While turbocharged engines can provide more power than a naturally aspirated alternative of the same size, naturally aspirated engines offer other advantages.

Naturally aspirated engines generally respond much more quickly to the accelerator - giving them what enthusiastic drivers would called greater response - whereas there can be a lag when suddenly asking for increased speed from turbocharged engines.

This turbo lag is the result of the extra complexity that ultimately allows turbocharged engines to make additional power.

Similarly, if you let engine speed drop too low, some turbocharged engines can feel very tardy as the turbocharger requires longer to recover and get back up to speed. This is not a problem for most naturally aspirated engines.

Furthermore, naturally aspirated cars should be cheaper to buy, more reliable and easier to maintain because they are less complicated.

Turbocharged models are also not always that economical in real-world driving, especially when working the engine harder - this can lead to large discrepencies between claimed and real-world mpg, particularly with turbocharged petrol cars.

Non-turbo petrols tend not to suffer with such large differences; Mazda, for example, has largely shunned turbocharging its recent petrol engines, and tends to deliver impressive real-world economy figures as a result.

You will find that non-turbo diesel cars are incredibly slow, however. As such they are best avoided.

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