The American Road, 1931
In 1931, the American road became a battlefield.
In one corner stood General Motors and its rapidly growing Detroit Diesel division—the industrial empire. Backed by immense resources, armies of engineers, and some of the largest research facilities in the world, GM believed the future belonged to speed, innovation, and mass production.
In the other corner stood Clessie Cummins, a former chauffeur from Columbus, Indiana.
GM built engines that screamed.
Clessie built engines that grunted.
General Motors wanted horsepower. Clessie wanted durability. While others chased speed records, he chased something far more valuable: an engine that simply refused to die.
To prove his point, he brought a diesel-powered race car to the Indianapolis 500.
The result would ignite one of the most important rivalries in transportation history—a battle between speed and endurance, innovation and reliability, corporate power and garage-born ingenuity.
It became known as the Horsepower Wars.
And for nearly a century, it shaped every truck, highway, and freight network in America.
The question is simple:
In the battle between the scream and the grunt, who actually won?
The Chauffeur Who Refused to Listen
In 1919, diesel engines were not considered suitable for vehicles.
They were enormous stationary machines used to generate electricity or power ships. Most weighed several tons and occupied entire rooms. Nobody seriously believed they belonged on roads.
Most engineers considered the idea ridiculous.
Clessie Cummins disagreed.
Born in Indiana, Cummins worked as a chauffeur for the wealthy Irwin family. He lacked formal engineering credentials, but he possessed an unusual gift: he learned by taking things apart and rebuilding them until they worked better.
William G. Irwin recognized that talent and invested $50,000 in Clessie’s experiments—a staggering amount of money at the time.
With that backing, Cummins set out to accomplish what many experts considered impossible.
He wanted to shrink the diesel engine and put it on wheels.
His reasoning was simple.
To defeat gasoline engines, diesel didn’t need to be faster.
It simply needed to outlast them.
That philosophy would define the Cummins brand for generations.
The Diesel That Challenged Indianapolis
In 1931, Clessie decided to prove his theory on the biggest stage in American motorsports.
The Indianapolis 500.
At the time, the Brickyard was the temple of speed. Lightweight gasoline racers roared around the track at astonishing speeds, often pushing themselves to mechanical destruction.
Into this environment rolled Car No. 8.
Powered by a Cummins diesel engine, the machine looked unconventional and sounded even stranger.
It didn’t roar.
It clattered.
Spectators reportedly viewed it more like a farm tractor than a race car.
Yet while competitors repeatedly entered the pits for fuel, repairs, and cooling-system issues, the diesel simply kept running.
Lap after lap.
Hour after hour.
Five hundred miles without a single pit stop.
The Cummins-powered entry finished 13th while consuming roughly $1.40 worth of furnace oil.
It did not win.
But it survived.
And that was the point.
The stunt proved that diesel technology could thrive in automotive applications. Reliability had entered the conversation.
The first shot in the Horsepower Wars had been fired.
GM’s Answer: More Power, More Speed
While Clessie focused on durability, General Motors focused on performance.
GM enlisted Charles “Boss” Kettering, one of America’s most celebrated inventors.
Kettering embraced a philosophy he called “Intelligent Ignorance.”
If nobody knows something is impossible, they might accidentally invent it.
When Kettering examined conventional four-stroke diesels, he saw inefficiency.
Why wait two revolutions for every power stroke?
Why not fire every revolution?
The result was the two-stroke Detroit Diesel.
GM invested millions into development. Originally designed for locomotives and industrial applications, the technology was eventually adapted for road vehicles.
The most famous version became the Series 71.
Compared to traditional diesels, it was lighter, more responsive, and dramatically more energetic.
Most importantly, it sounded different.
Very different.
The engine’s distinctive exhaust note, combined with the whine of its Roots blower, produced a mechanical scream that became legendary.
By the late 1930s, the battle lines were clear.
Indiana had the grunt.
Detroit had the scream.
Then the world went to war.
World War II: The Ultimate Test
When World War II erupted, the military needed power above all else.
The battlefield became the ultimate proving ground for both philosophies.
Detroit Diesel’s two-stroke engines found a home in Higgins landing craft—the boats that carried Allied troops onto beaches across Europe and the Pacific.
During the Normandy invasion, thousands of Detroit-powered vessels fought surf, tides, and enemy fire.
The military valued instant throttle response and high-revving performance.
Detroit delivered both.
Meanwhile, Cummins engines served a different purpose.
They powered generators, communications systems, radar installations, hospitals, and logistics hubs.
They rarely appeared in combat footage.
They rarely received recognition.
But they ran continuously under brutal conditions.
Day after day.
Night after night.
If Detroit helped win battles, Cummins helped sustain armies.
The war demonstrated a critical truth:
There wasn’t one perfect diesel engine.
Different missions required different strengths.
The Age of the Screaming Jimmy
After the war, America entered a golden age of growth.
Highways expanded.
Freight volumes exploded.
Businesses demanded speed.
For a time, the world belonged to Detroit Diesel.
Truckers nicknamed the Series 71 the “Screaming Jimmy.”
The name fit perfectly.
These engines howled down highways, powered Greyhound buses, operated fire trucks, and hauled freight across the continent.
Fleet operators loved them.
They were light.
Parts were interchangeable.
Repairs were relatively simple.
A competent mechanic could rebuild one almost anywhere.
But the Screaming Jimmy had a dark side.
Truckers feared a phenomenon known simply as a runaway.
If engine seals failed, lubricating oil could enter the combustion chamber.
Because diesel engines run on oil-based fuel, the engine would begin consuming its own lubricant.
Turning off the ignition did nothing.
The engine continued accelerating uncontrollably.
Faster.
Louder.
More violent.
Eventually, it either destroyed itself or exploded.
Veteran mechanics learned a terrifying lesson:
To stop a runaway, you had to choke off its air supply.
Sometimes that meant standing next to a screaming mechanical bomb and physically blocking the intake.
It was dangerous.
But it worked.
Clessie’s Greatest Invention
While Detroit chased performance, Clessie Cummins became obsessed with safety.
The inspiration came from personal experience.
During a cross-country demonstration run in 1931, Clessie nearly died descending California’s Cajon Pass when his brakes faded under heat.
He survived.
But he never forgot the experience.
Years later, he developed a revolutionary solution.
The diesel engine itself could become a braking device.
By releasing compressed air at the top of the compression stroke, the engine would absorb energy instead of producing it.
The truck would slow dramatically without overheating the brakes.
The invention became known as the compression-release engine brake.
Today, everyone knows it by another name:
The Jake Brake.
Ironically, Cummins management reportedly rejected the idea.
Clessie took it to Jacobs Manufacturing instead.
As a result, trucking history remembers the product as the Jake Brake—not the Cummins Brake.
It became one of the most important safety innovations ever introduced to commercial transportation.
Every rattling truck descending a mountain grade still carries Clessie’s legacy.
The Oil Crisis Changes Everything
For decades, Detroit Diesel dominated.
Then came 1973.
The Oil Crisis transformed fuel efficiency from a secondary concern into a matter of survival.
Suddenly, every gallon mattered.
Cummins recognized the opportunity.
Engineers redesigned their famous 855-cubic-inch inline-six and introduced what became known as the Big Cam.
The improvements increased injection pressure, improved fuel atomization, reduced operating temperatures, and boosted efficiency.
The engine wasn’t flashy.
It wasn’t exciting.
It didn’t scream.
It simply worked.
And it kept working.
Truckers quickly discovered that reliability and fuel economy generated more profit than raw engine speed.
The market began shifting.
For the first time, Detroit’s dominance appeared vulnerable.
The Australian Verdict
The final judgment arrived from one of the harshest environments on Earth.
The Australian Outback.
Road trains pulling multiple trailers across scorching deserts pushed engines beyond their limits.
Temperatures soared.
Dust infiltrated everything.
Failures became brutally expensive.
This environment exposed a fundamental weakness in Detroit’s two-stroke architecture.
Because two-strokes fire every revolution, they generate tremendous heat.
Under sustained heavy loads, cooling systems struggled to keep pace.
Reports of overheating and component failures became increasingly common.
Meanwhile, Cummins introduced the KTA-19.
This massive nineteen-liter engine seemed almost indifferent to the environment.
Its large oil capacity, conservative operating speeds, and robust cooling characteristics made it exceptionally durable.
Many accumulated extraordinary service lives before requiring major overhauls.
In the Outback—the industry’s ultimate torture test—the verdict became clear.
For heavy hauling, the four-stroke inline-six was king.
The scream sounded fast.
The grunt made money.
Detroit’s Collapse—and Rescue
By the 1980s, Detroit Diesel faced serious problems.
A generation of engines suffered from reliability issues, including the infamous “Green Leakers.”
One flaw, known as block fretting, allowed cylinder liners to wear against the engine block.
Coolant leaked into the oil.
Owners found milky sludge where lubrication should have been.
Engines failed.
Trust evaporated.
Even improved successors struggled to overcome the damage done to Detroit’s reputation.
Market share collapsed.
GM considered shutting the division down entirely.
Then Roger Penske stepped in.
The racing entrepreneur purchased a controlling stake and brought an entirely different philosophy.
He treated the factory like a race team.
Floors were painted white.
Processes were reorganized.
Quality standards improved dramatically.
The transformation worked.
Detroit Diesel recovered.
But Penske understood something critical:
The future would not belong to two-stroke engines.
The future would belong to computers.
The Digital Revolution
The 1990s transformed diesel technology forever.
Mechanical fuel systems had reached their limits.
Electronics promised greater precision.
Detroit’s answer was the revolutionary Series 60.
Unlike previous designs, it was built around electronic controls from the beginning.
The Detroit Diesel Electronic Control system—DDEC—used sensors and computers to calculate fueling in real time.
The result was better performance, better efficiency, and improved reliability.
The Series 60 became one of the most successful heavy-duty engines ever built.
Cummins responded with the N14.
Often described as “an 855 with a brain,” the N14 combined traditional durability with modern electronics.
The competition between the Series 60 and the N14 became legendary.
Many drivers still regard this era as the golden age of trucking.
The engines were powerful.
They were reliable.
And they used computers to improve performance rather than simply satisfy regulations.
For many enthusiasts, it was the perfect balance between old-school mechanical engineering and modern technology.
The Emissions Era
By the mid-2000s, everything changed again.
New environmental regulations introduced increasingly complex emissions controls.
Truck owners suddenly had to contend with three new acronyms:
EGR.
DPF.
DEF.
Exhaust Gas Recirculation.
Diesel Particulate Filters.
Diesel Exhaust Fluid.
Each system reduced emissions.
Each system also increased complexity.
Maintenance costs rose.
Reliability suffered.
The legendary million-mile engine became harder to achieve.
Many owner-operators responded by purchasing glider kits—new truck chassis fitted with older pre-emissions engines.
It was a clear signal.
The industry respected progress.
But it still valued simplicity.
The Modern Battlefield
Today, the war looks very different.
Detroit Diesel, now operating simply as Detroit under Daimler Truck, focuses on integration.
Its engines, transmissions, and axles function as a unified digital ecosystem.
The modern DD15 prioritizes efficiency, automation, and intelligent power management.
Cummins chose another path.
It remains the industry’s independent powerhouse.
Its engines can be found across multiple truck brands, preserving customer choice and platform flexibility.
The X15 continues the company’s long tradition of balancing durability, adaptability, and raw pulling power.
The philosophies established nearly a century ago still exist.
Detroit teaches trucks how to think.
Cummins teaches trucks how to work.
Who Won the Horsepower Wars?
In a sense, both sides won.
Detroit Diesel proved that innovation, electronics, and system integration could redefine transportation.
Cummins proved that durability, adaptability, and relentless reliability never go out of style.
Together, they transformed diesel technology from crude industrial machinery into the backbone of global commerce.
The screaming two-strokes are gone.
The highways are quieter.
Computers now manage tasks once performed by mechanical genius.
Yet every modern truck still carries traces of that original conflict.
The rivalry that began between a chauffeur in Indiana and an industrial giant in Detroit built the modern trucking world.
The noise may have faded.
But the wheels keep turning.
And nearly a century later, the Horsepower Wars still echo down every highway in America.
