When the flag dropped to start the 1931 Indy 500, 39 cars in the field that included Studebakers, Reos, Hudsons, Chryslers, Buicks, Fords, Willys-Knights and a Snowberger all had one thing in common, a gasoline-fuelled engine. The 40th was a Cummins Diesel Special powered by a boat motor.
This Sunday when the 33 runners start the 96th Indy, they'll all be driving virtually identical cars powered by same-spec engines from Honda, Chevrolet and Lotus, but the race was more open to innovation in the past. Along with diesels and just about every configuration of gasoline engine, there have been turbines, twin-engined cars and six-wheelers.
But innovation was particularly rife in the early 1930s when the Depression was making filling the grid a problem and race organizers responded with the "junkyard formula," which made stock block engines of up to 6.0 litres eligible along with the 1.5-litre pure sang supercharged motors then mandated.
So when engine manufacturer Clessie Cummins turned up and said he'd like to give it a try with a car powered by one of his big four-cylinder marine diesels, they said why not. At least on the understanding that in the unlikely event it won he'd get no prize money.
Indiana farm boy Cummins wasn't exactly an unknown at The Brickyard. A mechanically handy youngster who'd built his own car at 15, he was employed by Marmon in 1911 and part of the pit crew that serviced its yellow Wasp racer that won the first Indy 500 that year.
A few years later, he discovered diesel engines and, in 1919, formed Cummins Engine Co. to build them for farm, industrial and marine use, which it did with modest success.
When diesel power began to be used for trucks in the 1920, he set out to explore this new potential market. His first effort saw one of his engines installed in a used Packard limousine, which gained valuable publicity and was the first diesel-powered car built in North America.
Cummins' pioneering Indy entry was also essentially a publicity stunt designed to show the economy and durability of his engines, predating Audi's equally unlikely-seeming diesel assault on Le Mans by almost eight decades, but like it actually turning out to be a pretty racy effort.
Cummins turned to brothers Augie and Fred Duesenberg to create the Cummins Special, which they did by fitting the heavy 361-cubic-inch (5.9 litre), three-valve, four-cylinder yacht engine that thumped out 85 hp into a Duesenberg passenger car chassis. It was tested with a run on Daytona Beach and set a new diesel record at more than 100 mph (161 km/h).
Indy race organizers had stipulated it had to average at least 70 mph (112 km/h) but the hefty 3,389-pound (1,537-kg) racer qualified – at almost 97 mph (156 km/h) – dead last in the field in the hands of veteran Indy driver Dave Evans. Alongside him in the cockpit, specially padded to provide a little comfort as they planned to run the race without stopping, was riding mechanic Thane Houser, and in the trackside crew, aviation legend Jimmy Doolittle was handling the pit signals.
The white No. 8 Cummins special ran steadily and managed to avoid the usual race carnage to finish a more than respectable 13th. It had used just 31 gallons of fuel and one quart of oil for total running costs of $2.40.
Later that year, Cummins staged an endurance record-seeking run at Indy with a modified diesel powered truck that ran non-stop for two weeks and covered 13,535 miles, which impressed trucking operators. The race car was later fitted with a windshield and top and used for a 5,000-mile promotional tour of Europe.
But Cummins wasn't finished with Indy.
The company returned in 1934 with a pair of Duesenberg-based specials: one fitted with a two-stroke diesel (a technology some in the company were espousing), the other a four-stroke, both of them supercharged.
The four-stroke car managed only 81 laps in the hands of Evans before the gearbox disintegrated, but the two-stroke, after a series of problems, rattled home in 12th driven by gutsy Stubby Stubblefield, who finished with a foot badly fried by an overheated gearbox.
One story about the race says that when the engine was finally switched off, it seized solid and that Cummins, who was firmly in the four-stroke camp, had it removed and that night drove it to a nearby river to pitch it off a bridge. Cummins stuck to four-strokes after that, but didn't return to Indy again until 1950.
That year, Cummins engineers built a version of its huge JS-600 truck engine from aluminum rather than iron and supercharged it to make 345 hp. Powering a car dubbed The Green Hornet, it qualified in 33rd place at 129 mph and was running in 16th place when its crankshaft harmonic balancer went bang.
The company returned for one more try in 1952, with the engine now turbocharged and lying on its side to improve aerodynamics and lower the centre of gravity and, despite the low volatility of its fuel, set the place on fire.
Driver Freddie Agabashion took it easy during practice so as not to alarm Indy officials into a last-minute rule change, but on qualifying day let it all hang out, running a single lap at a record 139 mph and a four-lap average at 138 to win pole position on a shredding right front tire.
The race didn't go as well, with the car retiring on lap 71 after it was claimed the turbocharger inlet became clogged with track debris. But Cummins had already scored a promotional victory of inestimable value, it could now say to potential truck engine buyers: "Hey, the engine you're looking at won the pole at Indy."
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