No...it’s about 1.3x. But I agree that diesel engines are superior. They are also inherently fuel-flexible.
The efficiencies of a Diesel engine over a gasoline engine are inherent. It is in the design of the cycle itself. The Diesel cycle is more efficient than the Otto (Gasoline engine) cycle.
You can futz around all you want with Gasoline engines to remove some of those inefficiencies, and in fact a well designed turbo can do nice things for it, but there are "pumping losses" associated with the Otto cycle (basically, the engine has to use energy to "suck" air into the combustion chamber), that the Diesel cycle does not have. Thats one reason that Diesel engines get such good gas mileage on the highways, they only use as much fuel as they need to keep the engine turning over. In a gasoline engine, there is a significant amount of energy used in pumping/sucking the air through the intake manifold restrictions(the throttle basically). Diesels have no throttle, they are controlled by the amount of fuel that is injected into them.
That, plus the fact that they run at much higher compression ratios, which means that they can extract more energy from the fuel they burn.