12 Obscure Diesel Engines That Made Automotive History

Developed and patented by Rudolf Diesel, the diesel engine was designed to offer higher efficiency than the widely-used Otto gas engine, using higher compression ratios. Unlike gas engines, diesel fuel is combusted via compression, requiring no spark plugs. 

However, the diesel engine had quite a few obstacles to overcome in automotive history. It was often ridiculed for being underpowered. Diesels have also always been seen as less refined than comparable gas engines and known for emitting thick black smoke. Many manufacturers have tried to change that perception, on numerous occasions. Advanced technology like high-pressure common rail fuel injection and turbocharging solved some of the issues, and secured the diesel engine a moment in the spotlight. 

During its heyday, diesel engines actually outsold their gas counterparts in Europe, but they had to go through a lot of fringe designs and technologies before then, from the early days of compression ignition onward. Automakers were always eager to have the most fuel-efficient vehicle, which most often meant developing diesel engines. And in this piece, we'll have a look at diesel engines that existed on the margins of the industry, and made history for the right and wrong reasons. From seriously underpowered one-cylinder machines to race-winning turbodiesel beasts, here is our definitive list of the most obscure diesel engines ever made.

When most people think about diesel, the name Cummins probably springs to mind. The American manufacturer has been specializing in compression ignition for over a century now, and become one of the world's greatest developers of diesel engines. It all started with the Hvid four-stroke engine in 1919, developed to run equipment like pumps, corn grinders, or wood saws.

The Hvid engines were very rudimentary by today's standards. They didn't even have fuel pumps, for example, as fuel was fed into the precombustion chamber using gravity. For that reason, Cummins situated the single piston horizontally, with this being the distinguishing feature of the engine. Later, company founder Clessie Cummins improved the design by timing the ignition better. As a result, it made 6 hp, instead of the initially planned 5 hp. That's far from impressive, though the Hvid had a mere 1.0-liter capacity and revs only to 600 rpm. The most mind-blowing fact: It weighed almost 620 pounds! Damn, internal combustion tech has come a long way.

The Hvid engine had problems, though. Because carbonation from the precombustion appeared in the fuel cup, owners needed to clean it every few hours to ensure peak power. People also didn't know how to use the Hvid engine, as gas motors were more common at the time. Even so, Cummins' design was very reliable — there is an Hvid engine still running today!

Cummins brought the diesel engine to the forefront, but Mercedes-Benz was the first company to put one in a passenger car. Like Cummins' Hvid engines, Merc's unit had a precombustion chamber and Bosch indirect injection. Since compression ignition was in its infancy, the 2.55-liter four-cylinder wasn't particularly powerful, producing only 44 hp at a relatively low 3,000 rpm.

As a result, the 260 D could only reach 56 mph. That was also partly due to the three-speed manual, which in 1938 was replaced with a four-speed unit with synchronized gears. The diesel engine had other problems initially, like difficulty starting during the cold winter months. Fortunately, Mercedes-Benz also added glow plugs in 1938, which later became a standard fare on diesel engines.

Taxi drivers loved the 260 D for its 25 mpg, which was far higher than cars of the era. Thus, with the larger 13.2-gallon (50-liter) tank, the 260 D had a range of more than 300 miles. This was crucial, as gas stations weren't as common in the 1930s. Mercedes-Benz even made it available as a six-seat Pullman Landaulet model to cater to the needs of taxi drivers. After a short four-year production span, the German automaker sold 1,967 units — not bad for a novelty car!

Ever heard about opposed piston engines? It's a concept often used to manufacture large locomotive and marine engines, where two pistons face each other and share the same combustion space, leading to high efficiency. Due to their complex design, opposed-piston engines are rarely used in road-going vehicles, though effort was definitely made. Namely, in 1954 truck manufacturer Commer  offered a model with a Rootes TS3 opposed-piston, two-stroke diesel engine.

The unusual powerplant was quite common on the British company's trucks, and famously got the name "Commer Knocker." The 3.25-liter unit had three cylinders, but two pistons in each. Although both pistons moved similarly, one had a minimal lead to allow for better control over valve opening/closing. Rootes also added a supercharger for more power and torque. As a result, the TS3 made 105 hp and 270 lb-ft of torque, both amazing figures for a diesel motor in the 1950s. For comparison, the Mercedes-Benz OM 312 inline-six diesel had a 4.6-liter capacity and only made up to 90 hp.

Unfortunately, the TS3 was the last opposed piston diesel engine in Commer's lineage. Rootes Group, the company that engineered the engine, worked on a four-cylinder TS4 variant, but the project was scrapped after Chrysler bought the company. It's a shame, as despite its complex design, the TS3 has proven to be reliable.

[Featured image by SG2012 via Wikimedia Commons | Cropped and scaled | CC BY 2.0]

Mercedes-Benz brought the diesel engine into the limelight, but Peugeot really made it approachable for the regular buyer. Like each diesel story, this one had humble beginnings. Fitted to Peugeot's popular 403 family car, the 1.8-liter naturally-aspirated diesel was good for 47 hp. That's not bad for an engine developed in the 1950s, but the 403 was a relatively heavy car at 2,800-plus pounds. As a result, 0-62 mph took a lethargic 38.5 seconds.

And who cared about slow acceleration when the 403 Diesel was also good for 36 mpg on the highway? Families, especially those with tight budgets, certainly didn't! Sure, the 403 was styled by Pininfarina, but it was never built for speed and its super-economical diesel suited it well. For those that wanted a bit more oomph, there was a 1.5-liter gas engine with 65 hp, which could be further tuned with twin cams, aftermarket headers, and performance cams.

Still, it was the diesel engine that caught the audience's attention and helped the 403 get past one million sold units. As a result, Peugeot continued to push compression ignition engines into the mainstream, and in 1984 it launched the 604 GTD, Europe's first turbo diesel vehicle.

While Europeans have long enjoyed reliable and efficient diesel offerings, Americans needed to wait until 1977 for the first diesel-powered passenger vehicle. Developed and produced by Oldsmobile, the 5.7-liter unit was designed to solve the gas V8's thirst for fuel, while appealing to the American buyer's thirst for V8s.

Unfortunately, the Oldsmobile diesel was a huge sales flop and made history for all the wrong reasons. It was quite underpowered, producing a paltry 120 hp (105 hp after tighter emission regulations). It also had laughable reliability. Namely, in a genius move, Oldsmobile decided to use mostly the same parts from its 5.7-liter V8 gas engine. Of course, the diesel unit received sturdier pistons and crankshaft, but it was still leaking oil like a cracked pot and had huge issues with the injector pumps.

To add insult to injury, the engineers knew of the problems beforehand. "In test after test, we had broken crankshafts, broken blocks, leaking head gaskets, and fuel pump problems," said engineer Darrel Sand in a 1983 interview with the New York Times. "The diesel couldn't hold up, it was a hastily converted gasoline engine with a fuel pump designed for heavy trucks."

Oldsmobile still rushed its first diesel V8 to market, leading to a class-action lawsuit against the company. The State of California even banned the engine in 1979 and 1980, because it broke down during emission tests. Hey, but at least it got 30 mpg!

[Featured image by Greg Gjerdingen via Wikimedia Commons | Cropped and scaled | CC BY-SA 2.0]

A diesel motorcycle must sound like a joke to most, but we assure you — it's a thing. Royal Enfield's Taurus actually sold really well in India, and many examples are still roaming the country's streets. Why would anyone want a rattly diesel engine in a motorcycle? Fuel economy, of course! According to some reports, the Taurus could achieve a astonishing 190 mpg!

As you'd expect, the performance took a second stage here. To reach that astonishing fuel economy figure, Royal Enfield opted for a Greaves Lombardini 325cc single-cylinder engine, paired with a four-speed transmission. You'd say that this is a significant displacement for a small motorcycle, but it only made a measly 6.5 hp @ 3,600 rpm and 11.1 lb-ft of torque. Top speed: 40 mph. Entry into the rolling coal pantheon of greats? You bet! Yeah, revving this thing out was out of the question. But, also was visiting gas stations, as you could run this engine on the vegetable oil you used to make your French fries.

The Indian motorcycle manufacturer knew the 325cc unit was underpowered and later equipped the Taurus with a larger Greaves Lombardini 436cc engine, paired with a five-speed gearbox. Keep your expectations in check, though, because it only made one additional horsepower. Still, that was enough for a more usable top speed of 55 mph, with a similar fuel economy to the smaller engine.

Enjoying your modern direct-injection, turbocharged, and electrified wonder? Well, in Africa, people can still buy an obscure naturally aspirated 4.2-liter inline-six diesel. The colossally underpowered unit produces only 129 hp and 210 lb-ft of torque, and to make matters worse, it has to power the Land Cruiser 70, which weighs around 4,600 pounds.

Yup, driving that SUV must require discipline. But other than that, you can put any diesel fuel in the 1HZ, drive it for thousands of miles in the desert, and never care about repairs. It lacks power, sure, but the 1HZ has almost infinite reliability. Covering 600,000 miles without a rebuild is almost a given with this engine, and even if it comes to that, you can buy a full 1HZ engine rebuild kit on Amazon, and pretty much do the repairs yourself. Predictably, it's one of the most reliable JDM engines ever built.

The 1HZ is surely not exciting, especially not to the first-world car enthusiast. But most of the materials to make all modern cars we buy are mined in Africa, and the 1HZ-powered Land Cruiser 70 is an integral part of those operations. Put bluntly, it's the backbone of global manufacturing.

[Featured image by Berndw~enwiki via Wikimedia Commons | Cropped and scaled | CC-BY-SA 3.0]

Diesels are only good for larger vehicles. It's a statement you'll often hear in automotive circles, but not an entirely true one. Namely, the Smart ForTwo, a tiny 98.43-inch-long city car, was offered with a 799cc three-cylinder turbocharged diesel engine. The OM 660, developed by Mercedes-Benz, initially made 40 hp, though a high-pressure Common-Rail diesel injection system bumped the output to 45 hp in 2007.

That surely sounds underpowered, but for the engine's size, it's not too bad. The ForTwo still needed 19.8 seconds to reach 62 mph and couldn't get past 90 mph, but as a two-seater, this was strictly an urban dweller, anyway. Besides, its fuel economy was off the charts, at over 71 mpg combined. For a car, even one with only two seats, that's deeply remarkable.

Crucially, the OM 660 showed that tiny diesel engines have their place in passenger vehicles. Other manufacturers followed suit soon after, with Volkswagen offering a 1.2-liter three-cylinder diesel in the 1999 Lupo. VW's effort was even more geared toward fuel efficiency, with a mind-blowing 78.4-mpg combined rating.

By now you are probably wondering — are there any obscure diesel engines that were actually fun? Don't worry, as with the Mercedes-Benz C30 AMG CDI, we are going full throttle. This performance sedan/wagon/coupe made history as AMG's first and only diesel-powered machine. It was based on the W203-chassis C32 AMG, though equipped with a 3.0-liter inline-five turbodiesel, making a healthy 228 hp and monstrous 398 lb-ft of torque.

The OM 612 engine was used in many Mercedes-Benz vehicles of the era, including the commercial Sprinter Van. However, AMG did quite a lot of tune-up, increasing the capacity by 0.3 liters, and equipping the head with DOHC and four valves per cylinder. AMG paired the engine with a five-speed automatic transmission, which might just work well with a torquey diesel powertrain. 0-62 mph took 6.8 seconds, while the top speed was limited to 155 mph. Far from groundbreaking, sure, but perhaps quick enough for a vehicle that sips fuel at 31 mpg.

AMG also equipped the C30 AMG CDI with performance suspension, better brakes, and lightweight 17-inch alloys with performance tires. Crucially, the diesel-powered AMG remained rear-wheel drive for more fun through the corners. A sincere effort, it must be said, but not enough to lure buyers into showrooms. Mercedes-Benz sold only 691 units in the two-year lifespan, pushing this model firmly into obscurity territory. But it was to no one's surprise, as buyers were seduced by the superior gas-powered C32 V6 Kompressor and C55 V8 AMG.

You probably associate V10 engines with screaming supercars like the Lexus LFA and Porsche Carrera GT. But back in the 2000s, when Volkswagen was flying high during the Ferdinand Piech era, it produced a special V10 TDI mega-diesel, one of the most powerful diesel engines in the brand's history. This 5.0-liter unit was designed not only to give deep-pocketed buyers a more economical solution but also a potent one. With two turbines onboard, the V10 made a staggering 553 lb-ft of torque, similar to modern diesel-powered heavy-duty trucks. Yet, VW's V10 diesel was installed in land yachts, like the Phaeton and Touareg.

The engine's power figure of 309 hp is not as impressive, but turbodiesels were always about that torque anyway. Utilizing it, the V10 TDI pushed the 5,300-pound Phaeton to 62 mph in 6.9 seconds. Sounds slow? A gas-powered Lexus LS 430 V8 reached 62 mph in 6.3 seconds while weighing almost 1,300 pounds less. Power was sent to all wheels via a six-speed automatic. Economy figure: 20 mpg highway.

With that much power at your disposal and low fuel consumption, VW's most luxurious sedan seemed like a no-brainer for potential buyers. However, it was also very expensive and notoriously unreliable. The V10 TDI would break down almost annually, with massively expensive repairs adding salt to the wound. Technicians roll their eyes when they see one, as it's also very challenging to repair.

Audi is number two on the list of auto manufacturers with the most wins at Le Mans, amassing 13 championships throughout its short stint in the world's most popular endurance race. And the company's unmatched domination was mainly thanks to a diesel engine. The combination of high torque and unrivaled fuel efficiency helped the R10 V12 TDI open-top racer to amass five consecutive Le Mans victories, making it one of the most successful racecars in history.

But this wasn't any old diesel engine. The 5.5-liter V12 unit was fully made from aluminum to save weight, with the R10 tipping the scales at 2,039 pounds. It had four camshafts and four valves per cylinder. Two Garrett turbines and Bosch-sourced common rail direct injection were present, too, helping the diesel monster achieve 650 hp, with an overboost function pushing the figure to 800 hp. Predictably, the 811 lb-ft torque figure was much more impressive, but the fact that it was available at just 3,000 rpm is jaw-dropping. The engine was so long-legged that a five-speed XTrac semi-automatic transmission was enough to extract maximum performance.

Perhaps even more interesting is that a diesel-powered R8 road car was also in the works. Audi showed a production-ready R8 V12 TDI at the 2008 Detroit Auto Show, powered by a 6.0-liter bi-turbo V12 diesel producing 493 hp and 738 lb-ft of torque. It even had a six-speed manual, and reached 62 mph in just 4.2 seconds. Sadly, it was deemed too expensive and never reached production.

What is peak diesel? Well, there is one only answer to that question — the BMW B57D30C engine. One of the most complex internal combustion powertrains ever produced, this 3.0-liter inline-6 shows what happens when you throw every advanced technology at your disposal in one engine. Like four turbochargers, for example. Four! Two smaller, and two medium-sized. Predictably, featuring an intricate pipeline with bypass valves to make them sing.

Using those turbochargers, the engine made 400 hp @4,400 rpm and a whopping 561 lb-ft of torque available between 2,000 and 3,000 rpm. And if that doesn't sound impressive enough, 330 lb-ft were available from 1,000 rpm, thanks to a 48-volt starter generator that reduced turbo lag at lower revolutions. Inevitably, the B57D made the BMW M550d xDrive one of the fastest diesel cars ever produced. The performance sedan/wagon reached 60 mph in just 4.2 seconds and had a limited top speed of 155 mph. Theoretically, though, it could break the 186-mph barrier.

Impressed? Wait until you hear that it's also good for around 40 mpg! It has also proven to be reliable, despite being a complex piece of kit. Unfortunately, BMW had to kill it because its state-of-the-art technologies weren't enough to make it compliant with Europe's latest emission regulations.