Dr. Felix Wankel's rotary engine was arguably the most significant improvement on the internal combustion engine since the electric starter. If the auto industry had set out to eliminate its flaws instead of sticking with the reciprocating engine the "Wankel" would likely be powering most, if not all, of today's cars. Germany's NSU was first to put a Wankel into production with the Wankel Spider in 1964 (which I test drove at the time) followed by the sensational RO 80. NSU was then bought out by Audi but the latter's directors showed little interest in the Wankel, other than using the RO 80 body as inspiration for the Audi 5000. In the meantime Japan's Mazda saw an opportunity. It purchased the rights and dropped a 110 hp version of the Wankel into a limited-production, Miata-size sports car: the cosmo. Many years later television host Jay Leno found a Mazda Cosmo and ordered his technicians to swap the original Wankel for a later Mazda 12A rotary. A custom-built Weber carb and newer 5-speed gearbox are part of the conversion, which develops 220 hp, effectively doubling the Cosmo's power. Nigel Mathews took this photo during a recent visit to Leno's California collection.