Thermal Efficiency:
The optimal shape of a combustion chamber is spherical. When comparing piston engines to Wankel engines, it’s clear that the cylinder shape of a conventional engine is much closer to this ideal shape than the flat combustion chamber of a Wankel engine. There are several other factors at play here, but all of these combined result in the Wankel engine being less efficient, consuming more air and fuel per unit of power compared to traditional piston engines.
This is evident in the Wankel engine’s higher "Brake Specific Fuel Consumption" (BSFC) compared to piston engines. It’s hard to find directly comparable figures since BSFC varies with RPM and load, but both Google and ChatGPT agree that the Wankel engine typically has about 20-30% higher BSFC than a piston engine. In practical terms, this means the Wankel engine requires more fuel (and consequently more air) to produce the same power.

Volumetric Efficiency:
In terms of volumetric efficiency, the Wankel engine performs very well. It has no valves or other components that restrict airflow and has relatively large ports that allow air into the engine with minimal resistance. This means that Wankel engines utilize their theoretical capacity more effectively. While the engine may be less efficient in terms of fuel usage, it compensates by moving much more air and fuel for its given size. As a result, the size of the turbocharger must be significantly increased to achieve the same performance figures as a piston engine, simply because the Wankel engine consumes much more air.

OEM characteristics of the car. I will run with a flex-fuel sensor, and most probably be using 98 RON gasoline. Tho there is a ongoing issue with more and more fuel having ethanol mixed in. Our regular pump gas (95 RON) is now E10, and they are also talking about mixing that so either E5 or E10.