Efficiency & Power performance are two of the most asked questions when comparing between a diesel and petrol engine. The fundamentals of both engines are similar and the type of fuel burned by either power plant doesn’t change anything in relation to the engine’s general markeup. (e.g. a crankshaft spinning, connecting rods and pistons moving up and down, air being pumped in and exhaust being routed out.) Thus the basic architecture is very much the same. However what goes on in-cylinder in a diesel is vastly different from what you’ll find in its petrol-powered counterpart. The easiest way to explain the difference between petrol and diesel engines is with “air” and “fuel”. In a petrol engine, airflow is everything, you’re throttling air. A diesel mill is the polar opposite. It works on the premise of throttling the amount of fuel being injected – the air simply follows suit.