Clessie Cummins’ Cars
Cummins is synonymous with diesel engine power for trucks, earthmovers, boats, mining equipment and generators…but not passenger cars. That wasn’t Clessie Cummins’ fault, because he tried his damndest.
Clessie Cummins founded Cummins Inc in 1919, after a background in self-taught engineering that began with a steam engine he cast from molten iron he poured into wooden-framed moulds … at age 11. The steam engine powered a water pump on the Cummins’ family farm.
An intuitive engineer, Clessie left the farming life and became a mechanic with Marmon, where he helped develop the Marmon-Wasp racing car that won the inaugural 1911 Indy 500 at the now-famous ‘Brickyard’. He also impressed financier, William Irwin, who began a lifetime friendship and business partnership with Clessie.
After selling imported Dutch-made Hvid diesel engines for a few years, with constant improvements added by Clessie, the pair released Clessie’s own Model F (‘F’ for four-stroke) diesel engine design in 1924.
Via the Sears catalog, these engines were sold mainly to farmers, who didn’t understand the importance of clean air and regular maintenance, so the venture was plagued by warranty issues and was a financial disaster. Cummins Inc re-aimed its engines at on-road cars and trucks, and in boats.
In 1929, Clessie’s then-new, Model U, four-cylinder engine was slotted into a 1925 Packard and he ‘gate-crashed’ the 1930 New York and Atlantic City auto shows, having driven the diesel Packard from Indiana to New York with fuel an average consumption of 26mpg.
The economical automotive Model U variant was based on a marine engine design that produced 10bhp per cylinder – 40hp – but Clessie teased that output up to 60bhp in the Packard.
Orders for the Model U flooded in, but Cummins Inc lacked the production capacity to make them in large numbers. Negotiations with engine mass-producers were under way when the Wall Street stock market crashed in 1929. Luxury car diesel applications were put on hold, but truck, bus and boat makers still needed Cummins engines, so the company soldiered on.
However, Clessie couldn’t resist the temptation of a speed record attempt at Daytona Beach, so he tweaked the Packard engine some more and dropped it into a stripped-down Packard roadster. With 84bhp on tap – at a then unheard of engine speed of 1800rpm – the car clocked up a speed of 80.4mph.
Less than a year later, Clessie was back at Daytona, with a Fred Duesenberg designed, diesel-powered race car, based on a Duesenberg Model A chassis. The lightweight Model U engine was persuaded to develop 100bhp.
Clessie’s next car-power initiative was in 1931, when he entered the diesel-powered Duesenberg in the Indy 500. The Model U had bore and stroke dimensions of 4.5 x 6.0 inches, for a displacement of 382 cubic inches (6.3 litres). However, the engine size limit at the Indy 500 was 6.0 litres, so the bore was decreased by 0.125 inches.
The Cummins Diesel Special, Number 8, was the slowest qualifier, at 96.9mph, but it came 13th in the race, running on one tank of fuel, without making a single pitstop and averaging a respectable 86mph.
Number 8 was preserved by Cummins and is regularly displayed around the USA.
A still determined Clessie Cummins returned to the Brickyard in 1934 with not one, but two, diesel-powered Duesenberg cars. Number 6 was a two-stroke and Number 5, a new-design four-stroke, but both four-cylinder engines displaced six litres and featured aluminium construction and Roots-type supercharging. Both engines developed around 135bhp.
When the chequered flag fell, after 500 miles, the two-stroke car was placed 12th and the then-retired four-stroke car was given 19th place, following transmission trouble that sidelined it.
On the face of it, the two-stroke engine was the better performer, but, while the four-stroke had performed flawlessly during the race, the two-stroke had overheated and seized when it was shut down.
It’s rumoured that Clessie dumped the engine in a river on the way home from Indy. Thus ended Clessie’s dalliance with two-strokes.
The two-stroke car’s chassis was extended and fitted with a six-cylinder diesel. ‘Wild Bill’ Cummings recorded flying mile diesel car records in excess of 130mph, but these were non-sanctioned attempts and never officially ratified. This car has been restored by Cummins and is often displayed at events.
In 1935, Clessie had the Auburn Motor Company fit a new, lightweight, aluminium head and block, six-cylinder Model A Cummins diesel into an Auburn 851 sedan and drove it across the USA. The car recorded an amazing 40mpg and had a top speed of 90mph.
Sadly, Auburn-Cord-Duesenberg succumbed to Depression economics and folded in 1936, so there were no production Cummins-Auburns.
However, an Auburn 655 diesel car was preserved by Cummins and is displayed at its museum in Columbus, Indiana. It makes regular forays to historic vehicle functions, including the Auburn Cord Duesenberg Connersville Meet 2022 in August 2022.
In 1974, this Auburn was restored to its current condition and given to J I Miller as a 40th Service anniversary gift: J I Miller (then Cummins’ chairman) exiting the Auburn.
After Word War II, Clessie wasn’t finished with his car-engine fetish, despite the increasing acceptance of his truck, bus and marine diesels.
Cummins returned to the Brickyard again, in 1950, with a Kurtis Kraft chassis, fitted with a Cummins diesel, based on the JBS-600 truck engine. Number 61 was painted bright green and nicknamed the Green Hornet.
Its Roots-supercharged six-cylinder, 6.6-litre, crossflow-head engine was of aluminium construction and had four valves and twin injectors per cylinder. The injection system was a precursor to Cummins’ famous PT system. Output was 340bhp at 4000rpm and that proved inadequate, with the car qualifying last and being retired during the race.
Despite that setback, the Green Hornet was repaired and established several diesel-car speed records at Bonneville.
Undeterred by the 1950 Indy 500 failure, Clessie was back in 1952, with a new-concept car. Built once more on a Kurtis Kraft chassis, the Cummins Diesel Special, Number 28, had its turbocharged six lying almost on its side, giving the car a very low bonnet profile. Engine output had gone up to 430bhp at 4500rpm.
Although its wet weight of 3000 pounds and diesel engine characteristics limited its acceleration, Number 28 qualified third fastest and was running in fifth in the race, but was retired on lap 71, because of tyre debris clogging the turbocharger inlet.
Cummins preserved Number 28 and restored it in 2016, discovering a crack in the crankshaft that would have sidelined the car anyhow.
At the 2019 Indy 500, all five Cummins diesel-powered Indy cars were displayed.
Cummins Archive – text and photos
“Cummins at the Brickyard” by Karl Ludvigsen, Car Life (July 1969)
“Diesels at Speed” by Griffith Borgeson, Motor Trend (December 1950)
“The Triumph of the Diesel” Popular Mechanics (July 1934)