If nobody else, Clessie Cummins had proved to Americans the viability of the diesel engine.

The fuel economy that the Cummins engine exhibited at Indy managed to attract the interest of truckers; the next year, Kenworth became the first truck builder to offer diesels as an optional engine. Yet automakers still believed the diesel engine was too heavy for passenger car use. Clessie Cummins set out to change that perception.

In June 1935, he debuted the result of that effort: a 1934 Auburn powered by an experimental Cummins Model A six-cylinder diesel. Where all of Cummins's previous diesels used cast-iron engine assemblies, the Model A had an aluminum block and head, "making it more comparable in weight to a gasoline engine," according to Cummins company literature. A Time article announcing the Cummins-powered Auburn noted that the Model A, which developed 85 horsepower from 377 cubic inches, weighed 80 pounds more than the Lycoming straight-eight that originally powered the Auburn (870 pounds total).

Combined with a three-speed manual transmission and a two-speed rear axle, the 4,000-pound car was able to pull down 40.1 MPG on the first leg of a NY-to-LA transcontinental trip that Clessie planned to display the economy of the Model A engine. The trip, which lasted from June 17 to July 4, covered 3,774 miles and consumed just $7.63 worth of fuel; assuming the same fuel cost quoted in the Time article (and assuming my math is correct), that translates to an average of 44.5 MPG over the entire trip.

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