Fifth stroke? Here's how it works: two of the engine's cylinders, running with a conventional four-stroke design, fire and expend their exhaust gases into a third low-pressure expansion cylinder. A fifth stroke then allows those gases to expand, boosting thermodynamic efficiency. Due to this clever design, Ilmor estimates a five-percent improvment in overall efficiency versus a conventional direct injected engine of similar displacement.
Future plans call for a second generation of the technology offering up 150 horsepower and weiging 20-percent less than current engines. Interestingly, Ilmor engineering manager Steve O'Connor says, "We're looking for a manufacturer to back the idea, and the interest centres on its use in a hybrid application, as they tend to need sudden bursts of energy, and that is what this engine does well."
[Source: Ilmore Engineering via Autocar]