To get any noticeable power gain, the compression must be raised to outrageous levels, like 11:1 or higher. LP gas has an octane rating of approximately 110, but the vapor that's introduced through the air horn above the venturi displaces enough air to limit the power to approximately 85% of what's available on gasoline. If the compression is raised, the "dual fuel" capability goes away, as gasoline can't be used in an emergency. (Massive detonation/dieseling).
I worked for a California sand & gravel company that ran almost all their gas engines on LP, and only ran diesels in their big rigs like concrete mixer trucks. The technology is so primitive that even gasoline carburetion, let alone fuel injection, would be a major improvement. Now, figure out how to fuel-inject liquid LP and work all the bugs out, and you'll have something!
Jerry
