HISTORY OF CUMMINS, 1931–2002

Part 1

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Every manufacturing company has a foundational product. Sometimes, that product comes right away, but for the Cummins Engine Company, that foundational product came over a decade after its 1919 beginning. Its direct offspring continue in production today.

Much of founder Clessie Cummins’ early efforts with compressionignition technology involved the HVID system (pronounced “veed”). He quickly learned the limitations of HVID and moved past it, but his thinking also extended beyond engine designs and into engine markets.

First On-road Engine

By the end of the 1920s, Cummins saw a diesel market in the automotive realm—“automotive” meaning anything operating on the highway. Due to technical barriers, automotive diesels were generally regarded as impractical in this era and weren’t being widely pursued. Working toward an achievement in that realm, Cummins repowered a used 1925 Packard limo with one of the company’s most modern engines—a four-cylinder Model U marine diesel. Normally, this engine made 40 hp at 900 rpm, but Cummins tweaked it to make 60 at 1,300; and, in January 1930, he went on the road to make some news.

The Model U wasn’t an optimal swap for a car. The engine was huge, heavy and slow turning, but it took Cummins to shows around the country on a few dollars’ worth of fuel. It opened a lot of eyes, among them Henry Ford’s. Ford was encouraging but suggested focusing on the truck market.

Cummins had already figured that out, but he also knew he had to make a splash, and cars made the biggest splash. While on the tour, he was invited to run a diesel car in the March 1930 Daytona Beach Speed Trials. The limo was too heavy, so he “souped-up” the Model U a little more and put it into a stripped Packard roadster. On March 20, 1930, the car set an official diesel-powered car

record of 80.389 mph.

“Special Project”

In the fall of 1930, Cummins assembled his small engineering department and challenged it to update a Model U engine for a special project. A test engine was destroked to reduce the displacement from 382 to 361 cubic inches, and a second intake valve was added to specially built aluminum heads. There is some debate over how much it was destroked, and period sources disagree. Even Cummins historians Keith Baylor and Bruce Watson have not been able to resolve the question. Some sources say it was destroked to 360.8 cubic inches; others to 350 cubes. Without a teardown, there is no way to resolve the question.

About the same time, Cummins contracted with Duesenberg in Indianapolis to design a race car that could mount the updated Model U to set another diesel car record at Daytona Beach and to run the Indianapolis 500 race. The car ran at Daytona in February 1931, turning in a new diesel car record of 100.75 mph. On May 30, 1931, wearing number 8, it finished 13th at the Indianapolis 500—on one tank of fuel. On top of that, Cummins drove it home from the track and then to St. Louis on the same tank. These successes marked the beginning of the development of a new engine, soon to be known as the Model H.

The Model H

Cummins’ chief designer was Hans Knudsen. He and Cummins fleshed out the basic Model H design in August 1930 as Cummins was preparing the #8 Indy car and for a cross-country run in a Model U-powered truck. Plans coalesced around new fourand six-cylinder engines with a 4.875-inch bore and a 6-inch stroke, displacing 448 and 672 cubic inches, respectively.

A foundational element was the new Cummins Single-disc (SD) rotary fuel injection pump. Development had begun in 1928 for a pump to replace the individual pumps used for each cylinder, and the late Model U engines had them. Cummins wanted to manufacture its own pumps. However, certain designs posed manufacturing challenges, and the SD pump would provide an answer that lasted nearly 20 years in various iterations. The SD pump featured a rotating disk that delivered fuel according to the firing order, with a single highpressure pump supplying fuel and pushrod-actuated injectors timing and metering the spray.

10,000-Mile Test

A mere 23 days after its first start, the prototype H engine had been mounted in an Indiana truck. On December 12, 1931, Cummins, Dave Evans (the driver who raced the #8 car at Indy), Ford Moyer and Lt. Lawrence Genaro began a 10,000-mile, nonstop endurance run on the Indy 500 track.

 Built on September 15, 1932, this HA is approximately the 25th HA-600 production engine and is the earliest known surviving H-series six-cylinder. It was used for the 1935 Daytona Beach trials. It was updated with improved manifolding and a supercharger, raising the power output to 300 hp at 2,100 rpm on about 8 psi boost. Most likely, the pump was tweaked as well, but other mods are likely. This engine runs but has not been apart in a lifetime, so the internals are a mystery. It’s unclear why an early engine was used in the modified #5 race car three years after it was built.

 The Cummins Model U diesel used in the 1931 #8 Daytona Beach Indy 500 race car was the inspiration for the Model H. As this engine was being modified for the race, the prototype Model H engines were being designed and built by the same men. You can still see it at the Indianapolis 500 Speedway Museum. The engine was lightened as much as possible with aluminum, including the heads, which mounted an extra intake valve. This engine was tuned to make 85 hp at 1,800 rpm continuous, with short spurts up to 100 hp at 2,300 rpm.

 The Cummins HB four- and six-cylinder performance curves from 1937. The power ratings are nothing to brag about by today’s standards—but, man, look at the flat torque lines! Also check out that fuel consumption curve, peaking at about .4 lbs/hp-hrs at 1,000 rpm (about 5.2 gph) right there at peak torque. Not bad for a 672-cubic-inch engine!

 The four-stroke Indy race engine was a destroked HB-400 but was supercharged with a Switzercummins blower to about 8 psi. Like the two-stroke, it was rated at 135 hp at 2,500 rpm. It’s still mounted in the original #6 car and begs to go racing again.