Clessie Cummins Made Diesels the King of the Road… and Almost at Indy Too. Part Two

Ronnie Schreiber
by Ronnie Schreiber
clessie cummins made diesels the king of the road and almost at indy too part two

In Part One we looked at Clessie Cummins’ development of the first practical and reliable diesel truck engines and his earliest attempts to race diesels in the Indy 500. Though he had succeeded in developing the technology, he still hadn’t achieved the ultimate proof of concept that market success brings.

Until the early 1930s, what success Cummins had was by selling engines to trucking companies, not truck manufacturers. That changed in 1932 when Kenworth, a leading maker of large trucks, started offering the 100 horsepower, Cummins HA4 4-cylinder engine as a factory-built option.

To help promote that application, Cummins rented the Indianapolis Motor Speedway for a week to demonstrate the endurance of his engines. Stopping only for fuel, they drove one of his diesel-powered vehicles for 13,535 miles in 168 hours at an average 80 mph, and an average fuel mileage of 32 mph.

To market the engine to long distance truckers, Cummins had the Columbus factory outfit a tractor-trailer rig powered by one of his engines. For Cummins and the two mechanics who accompanied him, the trailer was equipped with two beds and a stove in addition to food and spare parts. A promotional deal was made with Continental Oil Company to supply all the fuel, fluids and lubricants needs plus one hot meal per person per day for the duration of the trip. The truck was shipped to New York City, where it set out westward to fanfare from the New York dailies.

The trip was not without incident. In southern Illinois, a coolant leak caused some overheating. Scavenging asphalt shingles from a roadside shed to use as patches they limped into St. Louis where they made full repairs and also replaced a bad fuel pump. An earlier record-setting PR event by General Motors resulted in some collapsed bridges not capable of bearing heavy trucks. That resulted in hassles from local officials and the need to find routes to avoid bridges. That meant fording a river in Texas.

A rocker arm in the engine failed and caused raw fuel to leak onto the exhaust manifold, which resulted in a fire that spread to the cabin, and scorched the seats and burned the feet of one of the mechanics. Once the fire was put out, they realized that the damage was minor and continued on.

Coming down the grade at the Cajon Pass near Barstow, California, Clessie Cummins was at the wheel and he experienced what was surely some peak-sphincter puckering when the trucks already inadequate brakes faded and failed. At the bottom of the hill there was a train crossing the road. Near panic, Clessie downshifted to slow the truck. Because diesels ignite by compression, if you shut the throttle hardly any engine braking is effected because almost 100 percent of the energy used in compressing the air is returned on the downstroke. The truck was still doing about 30 mph when it barely missed the caboose.

That feeling of helplessness and terror stuck with Cummins his entire life and later he’d do something about it, much to the benefit of truckers everywhere (if not to the hearing of folks who live near downgrades).

This time they got the publicity they wanted. Cummins set a new coast-to-coast record of 97:20, beating the previous record by over six hours. Trucking companies and manufacturers were impressed by the 15.75 MPG average. Orders began to grow. Sales increased tenfold to 100 engines a month. Mr. Irwin started to reap the benefit from his confidence in Cummins.

The revenue gave Clessie Cummins the freedom to work full time on R&D, pursuing experiments that couldn’t be done earlier due to financial straits.

Cummins wanted to look into two-stroke diesels. He wasn’t a fan of them, they smoked badly and had issues with lubrication, but there were rumors that GM was developing their own two-stroke diesel and Cummins wanted to stay competitive. Also, all of his earlier designs had been Otto cycle but Eddie Rickenbacker had instituted new rules at Indy allowing two-cycle diesels an extra 10 gallons of fuel for the race so Clessie decided to go racing again, this time with two different engines.

Cummins ordered two chassis from Duesenberg and built both two-cycle and four-cycle diesel engines. They had 364 cubic inches of displacement, were made of aluminum and supercharged. The four-stroke car qualified 22nd and the two-stroke started in 29th position. Dave Evans was driving the four-cycle but damaged the transmission on lap 81 when leaving the pits. A few laps later, the other car came in for driver relief, the pilot having burned his foot on the hot, exposed transmission housing. Evans took over and started to move up through the field, leaving clouds of blue smoke and heat trails in his wake. He finished in 12th place, still the best finish for a diesel powered car at Indy.

After the race, as the cars were sitting in the garage, as the two-cycle engine began to cool, the metal started to creak. Cummins didn’t have to break the engine down to know that it was seizing up. Furious, he closed the garage doors and he and one of his mechanics started removing the engine from the race car and loaded it in the back of a truck. On their way back to Columbus, they stopped on a bridge over the White River and they chucked the engine into the water below. Not a further word about making two-cycle diesels has ever been mentioned at Cummins Engine to this day.

Though Cummins’ engines were gaining popularity in the truck industry, he still hoped that diesels would be embraced by automobile makers as well. Automakers, though, considered them too heavy for passenger cars. To prove them wrong, in June of 1935 Cummins introduced to the public a 1934 Auburn powered by an experimental inline 6-cylinder diesel he tabbed the Model A. Unlike previous Cummins motors, which were made of cast iron, the Model A’s cylinder block and head were cast from aluminum and the 377 cubic inch engine put out 85 horsepower. A 870 pounds, it weighed just 80 pounds more than the Auburn’s original Lycoming straight-8.

Clessie took the diesel Auburn on another of his publicity tours, going coast to coast, New York to Los Angeles, in a little more than two weeks. They used just $7.63 worth of fuel, averaging over 44 mpg. E.L. Cord must have been impressed, because he contracted with Cummins to build three diesel powered 1935 Auburn airport limousines, likely for use by another Cord investment, the young American Airlines. Auburn put one on display at the 1936 New York Auto Show and there were rumors that the brand would be offering diesels as an option in all of their models.

That never happened. Cummins was said to have been worried about the Cord empire’s financial viability and he severed the relationship. One surmises that William Irwin had some input into that decision.

By the late 1930s, Cummins had 75 percent of the heavy truck engine market. Clessie earned more patents. When World War II broke out, Cummins became a favored vendor to military suppliers. By the end of the war, most truck manufacturers and all major trucking companies were using Cummins diesels.

By 1950, Clessie was in his 60s and semi-retired, with the company being run by his brother, Donald, also an engineer. It’s not known if it was Clessie looking for something to do or Donald wanting to promote the company, but Cummins decided to return to racing.

They entered a car powered by their latest engine, the JBS 600, a 401 CI inline six cylinder that put out 345 horsepower. Widespread use of aluminum helped reduce the weight of the large engine, and racing seemed like a good idea to promote those lightweight components. One component that wasn’t lightweight, though, was the crankshaft-driven Roots supercharger, which failed after about 50 laps. Though the car qualified in last place, 33rd on the grid, by the time it DNF’d it had passed half the field to be in 16th position when it retired.

By the following year, there was a war going on in Korea and the company had to expand to fill military orders, so racing was a low priority, though Clessie was working on one more assault on Indy, an effort that would leave a historic mark.

Problems with the heavy supercharger and another rules change had Clessie working on turbocharging. The rules at Indy allowed turbo diesels 6.6 liters of displacement. Don and Clessie had a 402.6 CI engine built, with even more weight reduction with aluminum and magnesium parts. Output was a very undiesel-like 380 horsepower, though even with all the alloy parts, the engine still weighed 750 pounds. Interestingly, none of the historical pieces I’ve found on the Cummins powered Indy racers mention the marquee feature of diesels: torque.

There were also production engine implications for turbocharging. Normally aspirated diesels can lose up to 25 power of their power at high elevations. Turbocharging would allow truckers to climb and cross the Rockies at full power.

In the 1930s, Cummins used Duesenberg chassis, but by the 1950s, Frank Kurtis’ Kurtis Craft chassis were dominating Indy and related racing series. Always an innovator, Kurtis had been experimenting with offsetting the driveshaft so it sat next to the driver, not below him. This allowed for a lower overall height and better aerodynamics. To take full advantage of the low driveshaft, the inline Cummins engine was flipped 90 degrees over on its side (as in some current BMW motorcycles). At the cowl, the Cummins Diesel Special was less than two feet tall. Sources say that the ’52 Cummins Diesel Special was the first Indy racer to have been developed with the use of a wind tunnel.

Though it was sleeker and more aerodynamic than the other cars entered, it was also more than 50 percent heavier at 3,100 pounds, due to the weight of the powerplant.

As it happened, the Cummins Diesel Special was the first car to attempt qualifying, with Freddie Agabashian at the wheel. He stunned the crowd and other competitors with a four lap average speed of 138.010 mph, a new qualifying record. None of the other 32 cars, including the Ferrari that entered that year, could match it and thus in 1952, decades before Audi and Peugeot diesels ran at LeMans, a truck engine company put a diesel on the pole at the Indy 500.

Knowing that the lighter cars could accelerate faster, the Cummins team knew they’d lose the lead in the race, but since it had the highest top speed, it was able to hold its own in the race, if not the lead position. However, after 175 miles the engine began to put out black smoke. No, they weren’t “rolling coal” — rubber debris, “clagg” from tires wearing, had clogged the air intake. Two laps later they retired.

The Cummins Diesel Special went on permanent display in the company headquarters, untouched from the race, still wearing its original tires. To celebrate the company’s golden anniversary in 1969, the car was torn down for a complete rebuild. They discovered that it was fortuitous that the intake had gotten clogged. Apparently there was a crack in the crankshaft which would likely have caused a catastrophic engine failure in just a few more laps. If you’re an engine maker, retiring due to a poorly placed air intake is better publicity than dropping out of the race due to an engine exploding.

Clessie Cummins never stopped developing the diesel engines that he loved. He retired from Cummins as chairman at 67 and in 1955 he started a new company, Cummins Enterprises, to develop and market his patents, which he still personally held. Always concerned with the time near Barstow when he tried to stop a runaway truck, he figured out a way to get a diesel to engine brake.

Clessie and his son, Clessie Lyle Cummins Jr., developed a driver-activated, solenoid-operated device that opens up the exhaust valve on one or more cylinders after the compression stroke. That effectively wastes the energy stored in compression and slows the truck. Cummins first approached the company he founded with the invention but they turned him down, as did other engine manufacturers.

Clessie Cummins, working on the “Jake brake”, compression release engine braking system for big diesels.

However, in a coincidence, Cummins’ nephew introduced him to the man who ran the Jacobs Chuck Company (maker of the standard three bit rotating drill chuck). Jacobs decided to market the device to the trucking market and by the end of the 1950s, the “Jake Brake” was commonplace on big rigs. Its use became so widespread that many municipalities have banned their use. The Jake Brake vents to the atmosphere unmuffled, resulting in unpleasant noise that some compare to turbocharged flatulence.

Clessie Cummins died at the age of 80 in 1968 in California, where he had been working as a consultant to the Allison company.

The company he founded would eventually win at Indianapolis, though not with an engine of their own. In 1987, some last minute deals put then three-time Indy winner Al Unser Sr. behind the wheel of a Roger Penske owned car, sponsored by Cummins. With The Captain playing pit strategy to perfection, Unser took the lead on the white flag lap and cruised to his fourth victory. Somewhere Clessie Cummins was smiling, though I’m sure he’d have rather Unser’s car had been powered by kerosene.

Photos of the Cummins Diesel Special by the author. Cummins had the car on display downstairs at Cobo for this year’s NAIAS, and also brought it out for the 2015 Concours of America at St. John’s. The full gallery can be seen here.

Ronnie Schreiber edits Cars In Depth, a realistic perspective on cars & car culture and the original 3D car site. If you found this post worthwhile, you can get a parallax view at Cars In Depth. If the 3D thing freaks you out, don’t worry, all the photo and video players in use at the site have mono options. Thanks for reading – RJS

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2 of 14 comments
  • Quentin Quentin on Oct 31, 2015

    "Interestingly, none of the historical pieces I’ve found on the Cummins powered Indy racers mention the marquee feature of diesels: torque." Because torque is literally a useless spec for a race car. For example, if you have a race car that redlines at 5000 RPM and the gearing is such that you're always between 3500 RPM and 5000 RPM, your peak torque at 2500 RPM literally doesn't matter. The race car, in an ideal world, will never be at that RPM.

  • Johannes Dutch Johannes Dutch on Oct 31, 2015

    A very interesting read. Several UK truckmakers (sadly all gone now) used Cummins diesels in the past. Brands like ERF, Foden and Scammell. And just like in the US, Ford also offered Cummins diesels. I remember the Ford D-series COE with the 504 V8 and the big Ford Transcontinental COE with the 14 liter Cummins. The main truckmakers from Continental Europe have always built their own diesels, with MAN and Saurer as the pioneers. MAN offered the first truck with a direct injected diesel engine in 1924, and in 1938 Saurer introduced the first truck diesel with a turbocharger.

  • NotMyCircusNotMyMonkeys for that money, it had better be built by people listening to ABBA
  • Abrar Very easy and understanding explanation about brake paint
  • MaintenanceCosts We need cheaper batteries. This is a difficult proposition at $50k base/$60k as tested but would be pretty compelling at $40k base/$50k as tested.
  • Scott ?Wonder what Toyota will be using when they enter the market?
  • Fred The bigger issue is what happens to the other systems as demand dwindles? Will thet convert or will they just just shut down?