[Caddylackn]

Propane as a fuel, has about 15-20% less energy than gasoline. If you raise your compression ratio and change your timing you can get a propane set up motor close to the output of a gasoline motor.

When used in a dual fuel motor, you have to pick one or the other setup. Usually it is set up as a gas motor, that can switch to propane but it will be down about 20% in power when using propane. IDK about gas mileage. They usually compare it as $cost of fuel per miles driven. Propane usually wins since its cheaper, that is why they use propane in fleet vehicles that do not need a very long range.