[serialk11r]

That's peak efficiency. Most current production car engines are ~36% efficient or so at peak, maybe a little higher.

Gasoline engines and diesel engines have very consistent performance across a wide range of rpm compared to turbines, which are not efficient at all short of max power.

40% is about the best you can do with a single cycle, combined cycle it is obviously higher. Gasoline engines of the typical design can probably hit 45% if optimized fully, I think. Extremely high compression ratio, simulated Atkinson, titanium rods/valves, race engine balance and friction reduction, should get you there or close (F1 engines are ~37% running at rpms so high the piston is about to outrun the flame front). A good exhaust heat regeneration system can probably pick up 5% more.

If you compare to what percent Carnot cycle efficiency at the same temperature ratio, current gas engines are like 50% of that, which to be honest isn't that bad. Much room for improvement sure, but it's not that bad.