Is it true that, capacity being the same, 2-stroke engines develop twice the power of 4-stroke engines?
According to simplifying theories, this is true. In practice, it is not at all so. A two-stroke engine has one working stroke (ignition/expansion) for every revolution, while a four-stroke engine has only half: because the working stroke is the only energy-producing (or power-producing) phase, we could be led to infer that, if the working displacement and average actual pressure are the same, a two-stroke engine develops twice the power of a 4-stroke engine. In fact, as can be drawn from general theoretical considerations, in a two-stroke engine, the average actual pressure is smaller than in a four-stroke, displacement cannot be fully used and the actual intake volume of fresh air is much smaller than the engine capacity (plus, some of the intake is lost into the exhaust port …). In current standard-production bikes, other characteristics being the same, we can expect approximately 10 to 15% more power from two-strokes; and in any case, four-stroke engines manage to fill this minor
