A naturally-aspirated engine refers to an internal combustion engine that is neither power enhanced with a turbocharger or supercharger. Most motor vehicle engines are naturally-aspirated engines; however, turbocharging and supercharging are currently a very popular way of boosting power output for a number car marques. Jaguar enjoys the benefits of its very quick supercharged models. Subaru, Saab, Mitsubishi and Nissan all have turbocharged models in their range of cars. Most road-going diesel-engine vehicles will use turbochargers and intercoolers too. This is because naturally aspirated diesel engines generally cannot offer a suitable level of power for everyday driving conditions.
In a naturally aspirated engine, the air/fuel mixture is forced into the cylinders by a vacuum caused by the cylinder movement, natural atmospheric pressure, and the venturi effect upon the opening of the inlet valves. In a turbocharged or supercharged engine, the fuel mix is forced into the combustion chamber under a greater pressure and this is therefore referred to as a forced induction engine.
When comparing a naturally asperated engine with a turbocharged or supercharged engine of the same displacement, the naturally aspirated engine will generally give less power. The simpler design of the naturally aspirated engines mean that they tend to be cheaper to produce en masse.
Many motor racing series like the big Aussie V8 Super-cars specify that only naturally aspirated engines be used in the cars to limit power and speed. NASCAR, Indy-Car and Formulas One sit also in this category. One of the main reasons for the limiting is also to ensure that the cost of producing the racing engines is not excessive and beyond the reach of some of the manufacturers. We hope that helps answer the question ‘What is What is a Naturally Aspirated Engine ?’!
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