The 1973 oil crisis played a part in frustrating the uptake of the Wankel engine. Mi with a large retractable propeller and a Wankel engine. The combustion chamber of the Wankel engine is an epitrochoid. Among other improvements researched were larger motors such as the Wankel engine. NSU invented the principle of the modern Wankel engine with an inner rotor. The rotational shaft speed of a Wankel engine is high compared to reciprocating piston designs. The core of the Wankel engine is the rotor, which creates the turning motion. The wankel engine would later be used in Norton machines. The Wankel engine (rotary engine) does not have piston strokes. Mercedes-Benz fitted a Wankel engine in their C111 concept car. The Wankel engine is actually a variable-volume progressing-cavity system. The Wankel engine has problems in fuel efficiency and emissions when burning gasoline. All these points lend the Wankel engine as ideal for hydrogen fuel burning. A GM two-rotor Wankel engine powered the car through a new transaxle. After years of development, Mazda's first Wankel engine car was the 1967 Cosmo 110S.