Propane Powered Engines Featuring a 7.3 Ford and 6.7 Cummins

a spark ignition engine designed for propane operation is capable of high power output and efficiency, since propane like alcohol has a higher octane rating one can run much higher compression and much more spark advance.

Course it will use more gallons of fuel than gasoline due to the lower energy content, but it gains in thermal efficiency to partially offset.

Dual fuel engines another story, spark advance can be adjusted but not easy to adjust compression ratio.