NA is short for Normally Aspirated.
This means the air entering the cylinders is sucked in by the vacuum created when the cylinder travel downwards with the inlet valves open. UK Mk1, UK GT, UK Coupe, JDM G-LTD and MK3 are all NA design.
This is the opposite to turbo charged or supercharged forced induction engines. This means the air is forced under pressure, into the cylinders.
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