1927 Miller Model 91

The Miller 91 models were powered by 91 cubic-inch (1.5-liter) supercharged straight-eight double overhead cam engines offering 250 horsepower at 8,000 RPM, giving them top speeds in excess of 170 mph. They were so successful in motorsports competition that they dominated speedways for the 1920s and were effectively responsible for their own demise. In 1930, AAA's rule change to the 'Junk Formula' was done to essentially stop the Miller 91's seemingly unending winning streak.

Rule changes for the 1926 racing season limited displacement to 1.5-liters (91 cubic inches). The 122-cubic-inch Harry Miller engine could have been modified to comply with these changes by simply shortening the stroke, but instead, Miller and his staff began work on an entirely new car.

The Miller 91 and the preceding 122 were completely different, with only minor components shared between the two, including the wheels, tires, electrical components, and instrumentation. They were virtually identical in appearance, except for the 91's three-piece radiator and grille assembly. At the time of introduction, the supercharged 91-CID engines offered 155 horsepower at 7,000 RPM, with further development bringing this figure to over 250 horsepower at 8,000 RPM.

The Miller 91 was built in both front- and rear-wheel-drive configurations. In 1929, the Packard Cable Company sponsored a trio of new Miller 91s for American National Championship racing; two front-drive versions driven by 'Leon Duray' (real name George Stewart) and Ralph Hepburn and a rear-drive variant for Tony Gulotta. Duray took the two gleaming front-drive cars on a European tour, setting records at Montlhéry near Paris, France, and then at Monza Autodrome in Italy.

Complications arose due to the excessive racing wearing out the vehicles, and 'Leon Duray' eventually ran out of money. One of the spectators was Ettore Bugatti, who was so impressed by the Packard Cable Special Millers that he offered Duray a deal, trading the pair of Millers for three Type 43 Bugattis. The Miller engine would later inspire the road-going Bugatti Type 50 and the Grand Prix Type 51. The Miller engine was based on the successful 1913 Peugeot racing engine. The 181 cubic-inch straight-eight Miller engine had a valve-train featuring twin overhead camshafts, which would later characterize American track racing engines and culminate with the long-dominant Offenhauser in-line four-cylinder design.

It is estimated that 12 to 13 rear-wheel-drive Miller 91 examples were originally built. They successfully raced on a variety of surfaces and in various races. They competed at the Indianapolis Motor Speedway, dirt tracks, and steeply banked board speedways in Culver City, Atlantic City, Fresno, CA, Altoona, PA, Atlantic City, NJ Woodbridge, NJ, Miami, FL and many tracks where speeds were even higher than at Indy!

by Daniel Vaughan | Mar 2020