A Guide to Naturally Aspirated Engines

Naturally aspirated engines (also often referred to as normally aspirated engines) are standard petrol (and sometimes diesel) internal combustion engines. They are called ‘natural’ here because the air supply is based on atmospheric pressure rather than on the addition of any kind of turbo or super charger.

These kinds of engines are driven by air or a mix of air and fuel into their cylinders. The air/fuel goes through a filter and is then is forced down into the cylinders themselves by a vacuum effect which is in turn created by atmospheric pressure, a process known as the Venturi effect and the cylinders themselves. The movement of pistons within the engine and also sometimes the working of the exhaust system then reduces cylinder pressure so that incoming air has somewhere to go.

Naturally aspirated engines are more cost effective to manufacture than engines with a turbo or super charge but they are also not usually as powerful. Naturally aspirated engines cannot drive the pressure in their cylinders to below the standard level of the vacuum and their atmospheric pressure is limited so - in very basic terms - the flow of air into the combustion area of the engine is restricted. By adding a turbo or super charge the engine can get more air and/or fuel into the cylinders at once so performance is improved.