Someone had the great idea of putting a high-pressure, heat-resistant camera inside the cylinder of a four-stroke engine. Shooting at 1000 fps, the camera recorded just exactly what happens to make engines run. Suck, Squeeze, Bang, Blow! [LiveLeak]
This could be a GM car with a "waste spark." Instead of a distributor, there's a coil pack that fires two cylinders at a time. When the cylinder on combustion fires, the cylinder on exhaust also fires. I believe the main reason is then there's fewer moving parts to break/ draw power from the engine.