Here’s how it works: The engine starts with the familiar intake, compression, and power strokes. But instead of moving directly to exhaust, it introduces a second compression and power stroke before finally completing the cycle with an exhaust stroke. This 1080-degree combustion cycle is made possible by a unique crankshaft mechanism that varies the piston stroke length between about 83 and 118 millimeters during the cycle. At a certain point, side ports in the cylinder wall open to allow fresh air—likely pressurized by a turbocharger—to scavenge the cylinder, pushing out remaining exhaust gases and filling the chamber with fresh air for the second combustion event.
The result is two power strokes for every three crankshaft revolutions, effectively increasing the frequency of power delivery compared to a conventional four-stroke engine. This could translate into a roughly 23% power increase for the same engine size and RPM, potentially boosting naturally aspirated engines like the Porsche 911 GT3’s 4.0-liter flat-six from 500 to around 600 horsepower without forced induction.
Beyond power gains, Porsche’s six-stroke design aims to improve thermal efficiency and reduce emissions by enabling a more complete burn of the fuel-air mixture. The additional scavenging stroke helps clear out residual exhaust gases, allowing the second combustion to take place in a cleaner cylinder environment. This could push thermal efficiency toward 45-50%, a significant improvement over current four-stroke engines.
However, the design also introduces complexity. The specialized crankshaft with concentric rings and variable piston strokes adds mechanical intricacy and potential friction losses. How this affects engine balance, vibration, and durability remains to be seen. Moreover, the second power stroke follows a very short scavenging period, raising questions about its power output compared to the first.
While six-stroke engine concepts are not entirely new—early ideas date back to the late 19th century—Porsche’s patent represents a serious, modern attempt to revive and refine the concept. It reflects the brand’s commitment to pushing combustion engine technology forward, even as electrification gains momentum.
If successfully developed and implemented, Porsche’s six-stroke engine could offer a compelling blend of increased power, improved efficiency, and cleaner emissions, extending the relevance of internal combustion engines in a rapidly evolving automotive landscape. For now, the engineering details remain closely guarded, but the patent signals exciting possibilities for the future of performance engines.
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