Back in the old days of the Cam Wars, Isky used "The Five-Cycle Cam" as a marketing gimmick. Now, one of his old rivals, Bruce Crower, has come up with a six-cycle engine. Starting with a diesel one-lunger, Crower converted it to petrol use. He then added a water-injection cycle that uses steam formed by the superheated exhaust to push the piston back down again. He's now working on developing a diesel version that he thinks would be highly beneficial for long-haul truckers, offering the same power, but with more fuel economy. Plus, it eliminates the need for a cooling system. [Thanks to Brian for the tip]

Six-Stroke Engine Concept [Gear 6]

Related:
Hydrogen Injection: Can it Increase Fuel Economy? [Internal]