~30% efficiency, and around 40MJ of energy in a Kg of diesel. That means ~700hp/kg of fuel per hour, at a rate of 100kg per hour, the engine, fuel system, lubrication system, forced induction system, and cooling all take up space and add weight. Engines are the heaviest part of the car. With an electric car, the motor drive, and cooling system are more compact and energy dense than a combustion engine, the battery storage is not however. So there is a tradeoff. If you could have the same energy density as fuel, and the energy density of electric motors, you'd have an ideal scenario. Hybrids try to get there, by using fuel to run electric motors and batteries. Turbine engines are prohibitively expensive, both to manufacture and design, so that wouldn't work on a car. It's a tricky scenario for sure. I agree with Musk, that it's overall cheaper and more efficient if everyone gets their energy from the same source. To put into perspective how expensive it is to design and manufacture turbine engines. One reasonably intelligent engineer will collect low 6 figure salary just to work on one compressor stage in a 5 stage compressor. He works with an entire team of people to make sure his tinkering doesn't fuck up everyone else's tinkering and vice versa.