11 Huge Engines With Surprisingly Low Horsepower

The 1970s progressive rock band Rush has got to be one of the most impressive musical groups of all time. Why? Not only did they influence an entire genre, but they did it using only three band members. Each one worked overtime, playing multiple instruments and extracting the absolute maximum out of their sound.

We’d argue that this same convoluted labyrinth of an analogy can be applied to some of the best internal combustion engines of all time. Take the Honda FC20, for example. Widely considered among the greatest four-cylinder engines in automotive history, it had just 2.0 liters of displacement, but delivered 240 naturally aspirated horsepower, equating to an incredible 120 horsepower per liter at the time of its debut.

Or maybe the Ferrari 458 Italia, which made 562 horsepower from its god-like 9,000 rpm naturally aspirated 4.5-liter V8, coming out to nearly 125 horsepower per liter. Like Rush, these engines were all hands on deck, stretching their bandwidth to the very last atom, and achieved monumental outcomes despite their lack of size. But this isn’t about those masterpieces. Instead, we’d like you to imagine the polar opposite side of that spectrum.

We had to enter the Cadillac 500 first because, let’s be honest, it’s basically used as shorthand for this concept by now. But that’s only because of where it ended up — when it debuted, this motor was actually quite ferocious. In 1969, GM’s Cadillac subsidiary debuted the largest passenger engine available for sale, the 472 big-block. But a year later, the company wanted to add an air of exclusivity to their flagship Eldorado model, and what better way to do it than plop in a bespoke engine.

What came out was the Cadillac 500 cubic-inch V8. Designed as a stroked out evolution of the 472, the whopping 8.2-liter titan was capable of 400 horsepower and 550 pound-feet of torque, handily putting it near the top of the horsepower hill. But with the 1970s came frightening new hurdles. Increased concern over carbon pollution, as well as the oil crisis that led to the CAFE standards (Corporate Average Fuel Economy), resulted in regulations that killed horsepower and propped up fuel efficiency.

The effects on former high-performance American engines were immediate, and in the years following, finding factory-built cars with more than about 250 horsepower was a rare encounter. The Cadillac 500, specifically, was among the biggest victims, as by 1976, cars equipped with the optional 500 V8 (like the Eldorado) were making as little as 190 horsepower from its 8.2 liters. If you do the math, it comes out to a sad 23 horsepower per liter.

The Detroit Diesel, as much flak as it receives, was a formidable workhorse engine for decades of GM products. And though it would be considered (severely) low tech by today’s standards, this engine was quite the headline back when it debuted in 1982. It was GM’s first diesel built from the ground up specifically for truck use, as the previous 5.7-liter diesel V8 it replaced was originally a gas-powered unit reworked to operate on diesel.

But enough pleasantries — why is this engine on this list? For much of the 6.2-liter Detroit Diesel’s production cycle (1982 to 1993), it made just 130 horsepower and 240 pound-feet of torque. That was just functional enough for the average towing job in the early 1980s, and the fuel economy was about 25% better than comparable gas truck engines, but in hindsight, those 130 horses were working overtime to move those heavy 4,500+ pound trucks.

In the very same year, Mercedes-Benz’s new 3.0-liter five-cylinder turbo-diesel made a comparable 120 horsepower with three fewer cylinders and 3.2 fewer liters of displacement, albeit with some more expensive technology like turbochargers. Still, the 6.2 was a certified dog. Interestingly, the Detroit Diesel is also the reason why you’ve heard stories of military Humvees being so slow. That’s right, a slightly upgraded 150-horsepower version of the 6.2 was used in the original M998 HMMWV, and with all that extra armor weight, the Detroit Diesel earned its gutless reputation.

The 6.75-liter L-Series V8 holds deep historical importance, possibly more than any other engine on this list, but as you’ll read, it certainly had some low points. Originally developed under the umbrella of Rolls-Royce (Bentley’s former owner), the L-Series V8 debuted in 1959 in the Bentley S2, replacing the outdated straight-six. Back then, the L-Series was far from a 6.75-liter machine, though, displacing just 5.2 liters in prototype form, and then 6.2 liters once it hit production.

The famous 6.75-liter delineation first appeared in 1965, powering both Bentley and Rolls-Royce models for more than 30 years with various power ratings. Within those 30 years, however, came the L-Series’ low point, as in the 1991 Rolls-Royce Corniche, the 6.75-liter would only make 215 horsepower. Seven years later, in 1998, Bentley and Rolls-Royce would finally part ways, as Rolls was now to be a part of the BMW group, utilizing their powerplants for future models. It wasn’t the end for the L-Series, though, as it would continue in Bentley models like the Mulsanne for many years.

The L-Series became famous for its low-end torque and trademark British smoothness that had been baked in since 1959, but some six decades later, Bentley decided the “six and three-quarters” had served its purpose, and in 2020, it said goodbye to the L-Series, honoring the motor with a final “Mulsanne 6.75 Edition” by Mulliner, where it would make 530 horsepower as well as a hearty 811 pound-feet of torque at just 1,750 rpm.

While countless American engines met their end at the onset of the 1970s emissions-regulated Malaise era, the Oldsmobile 5.7-liter diesel V8 was a direct product of it. Automakers weary of the short timeline allowed to comply with new regulations had to get creative, and for Oldsmobile, this meant dusting off their old homework.

While some manufacturers reacted to the new eco-friendly industry standards by developing brand-new downsized fuel-efficient motors (like that 3.0-liter Mercedes turbo-diesel from earlier), Oldsmobile took their existing 5.7-liter gas V8 and converted it to run on diesel fuel — a process which included a rework of the entire unit; block, heads, fuel system, and all. By 1978, their work was done, and in most applications, the new “LF9” made 120 horsepower. Not too much worse than the Detroit Diesel that would come 4 years later (only 10 horsepower difference), but still properly feeble.

Only, it would get worse, as by the time the Detroit Diesel actually debuted in 1981, the Olds oil burner was further detuned to make just 105 horsepower, for a ratio of only 18.4 horsepower per liter. Oldsmobile’s underachieving diesel would find its way into (probably too many) GM products over the following years, covering several Cadillacs and most of Olds’ own lineup. But after the LF9 started clogging injectors, leaking oil, and breaking headbolts (among many other issues), it was promptly discontinued in 1985, and GM would ditch non-utility diesel vehicles for good.

In the 1990s, both Ford and Dodge would debut their end-all be-all truck engines, and both happened to come in 10-cylinder form. Dodge with its iron-block 8.0-liter and Ford the 6.8-liter Triton unit, leaving GM toiling about with their lowly 8-cylinders. But sure enough, by the turn of the century, GM would go bigger than all of them, when in 2001, the world would lay eyes on the new Vortec 8100 V8.

Intriguingly, this 8.1-liter hog of an iron lump was based on the iconic 454 big-block, and included, among other things, boosting the 454’s usual stroke of 4.00 inches to 4.37 as well as raising the deck height with rods and pistons to fit. GM also fitted a burlier head bolt pattern and additional end-cap bolts on the bottom end, for maximum durability. As far as power goes, the 8100’s 340 factory horsepower is certainly better than our other entries, especially the comparable 8.2-liter Cadillac from before.

But that was nearly 30 years removed from the pathetically underpowered Caddy, and the pessimist in us says that getting 340 horses from more than eight liters in 2001 is almost just as bad. On an even more depressing note, the Vortec 8100 was the last big-block Chevy we ever got. The 8100’s 761-pound weight could only be used by trucks and utility vehicles, and by 2009, GM ditched the idea, focusing on the small-block and its wider array of applications.

Call it unfair, but we’re going back 90+ years for our next pick. Enter the Bentley 8-liter straight-six. Even though this engine debuted all the way back in 1930, the 8-liter six was the last (and biggest) in a lengthy line of Bentley straight-six engines developed since 1921, and because this was to be the best one yet, founder W.O. Bentley had a certain spectacle in mind — a 100 mph car. The 8-liter was developed using the previous 6.5-liter engine by increasing its bore to gain 1.5 liters of displacement. The motor also received a larger radiator and various lightweight components. In fact, the crankcase of the 8-liter was made entirely of magnesium alloy… in 1930.

The new engine now made 200 horsepower in low-compression configurations (25 horsepower per liter); Unquestionably weak by today’s standards, but still somehow better than the Cadillac 500. Bentley’s engineers insisted that when finished, the new car would be able to reach 100 mph regardless of the lavish custom coachwork chosen by buyers. And they were right. The cleverly named Bentley 8 Litre was capable of 101 mph in its 1930 debut, thanks to its high-tech four-speed transmission.

Another fun thing that happened around 1930 was… the Great Depression. This global economic collapse irrevocably marred the release of the Bentley 8 Litre, so much so that only 100 units were ever built between 1930 and 1932, and soon after, Bentley would undergo an ownership change.

Funny enough, Bentley’s new owner would be none other than Rolls-Royce, who also happened to have a gigantic straight-six in their inventory. It was a massive 7.7 liters in displacement, featured an overhead valve design, and made just 120 horsepower(15.5 horsepower per liter), so if you thought the Bentley was slow, think again.

The 7.7-liter we’re talking about wasn’t actually the first to have that exact displacement, as the Rolls-Royce Silver Ghost used earlier versions of the straight-six in 7.0, 7.4, and 7.7-liter displacements before the updated 7.7 came in 1929 for the then-new Phantom II. This new model was one of the marque’s biggest yet, weighing in at around 7,000 pounds, and though the engine’s 120 horsepower was still considered powerful for the era, even co-founder Sir Henry Royce said the straight-six was reaching its limits.

Was he lying because he was embarrassed by Bentley’s ability to get 80 more horsepower out of a straight-six in the same year, or was he a fortune teller who knew that WWII was right around the corner and would spell the end for the 7.7-liter anyways? Who knows. The fact remains, though, the 7.7-liter would be the brand’s final pre-war straight-six, and the 7.4-liter V12 that would succeed it under the hood of the Phantom III was Royce’s final major project before his death, in 1933.

Dodge’s Hemi engine might get all the googly eyes and attention from muscle car folks, but in our opinion, the 440 was the true street king. Debuting for production in 1966, the 440 was an evolution of the 413 cubic-inch V8, sharing the “wedge” combustion chamber and “RB” (raised block) design that would define Chrysler’s big-blocks of the era. To make the 440, engineers simply bored out the 413’s cylinders for extra displacement, and in the early years, the 440 was making up to 375 horsepower across its applications in Chrysler products.

It was a more conventional and usable hot rodding engine than the race-bred 426 Hemi, and for buyers at the time, it was also less expensive to option. But as time went on, well, you know the story: The 1970s hit, heavy regulations were implemented, and the V8s got hit where it hurts. By 1978, the life was all but drained from the 440, as in some full-size sedan and truck applications, it was breathing through a 2-barrel carburetor and making just 200 horsepower.

As 1978 charged on, the 440 became entirely unfeasible for Chrysler. Its husky size and aversion to strict emissions tests were glaring, and production of the 440 would cease at the end of that year. It made its mark, though. More than 750,000 440s were built in those 13 years, and they are still incredibly popular for folks who want to swap big power into their old Mopars.

The Ford 460 was a part of an exciting new class of V8s from the blue oval. Dubbed the 385-series engines (named for their 3.85-inch bore), Ford debuted the 370, 426, and 460 cubic-inch engines for use across several segments starting in 1968. These three were lighter and more powerful than their FE and MEL predecessors. The 460, often called a “Lima” engine because of its origins at the Ford factory in Lima, Ohio, was the biggest and most exclusive of the 385-Series motors, initially only reserved for use in fancy Lincoln models. And safe to say, those big boats were moving. 

The 460 provided a stern 365 horsepower and 485 pound-feet of torque, more than enough to move a four-door Continental in the late 1960s. Unfortunately, the glory days were short-lived. Even in the early 1970s, exacerbated by the growing requirements for brands to advertise “net” horsepower rather than “gross” horsepower (basically, crank hp vs. wheel hp), the big 460 was rated at only 208 horsepower. It would stay on this trajectory as emission regulations took a firmer hold, hitting rock bottom in 1977 with a factory rating of 197 horsepower.

But, unlike Chrysler’s 440, which was killed off before the 1980s, Ford found a use for the 460 all the way until 1998, when it was finally discontinued. It only sustained minor adjustments through all those years, depending on the current regulations, and in the end, it was Ford’s longest-serving big-block to date.

It’s high time we expand our shaming session beyond the U.S. and Britain. Germany, it’s your turn. Introducing the Mercedes-Benz M100 V8. The 6.8-liter actually began life as a 6.3-liter unit, which was initially used to power the long-bodied Mercedes-Benz 600.

Long story short, the legendary late Mercedes engineer, Erich Waxenberger, wanted to prove to the journalists that Mercedes was capable of more than boring estate cars. Thus, he took the rolling chassis of a 300SEL and stuck the 6.3-liter V8 under the hood. His colleagues loved it so much that it actually went into production, and later to the racetrack. But he wanted more, and subsequently punched the 6.3-liter V8 out to a 6.8-liter, and stuffed it into yet another 300SEL.

Dubbed the “Red Pig,” this racecar was one of the most famous of all time, and even took second place at Spa in its debut. All of Waxenberg’s successful shenanigans led to Mercedes allowing him to put the new 6.8-liter V8 into the newly developed 450SEL sedan, and by 1975, it was in production, making an impressive 286 horsepower. But just a couple of years later in 1977, U.S.-spec 450SEL models were detuned for only 250 horsepower. We know, it’s not that big of a deal, and yes, bigger American V8s were making less at the time. However, by today’s standards, 250 horses from 6.8 liters would never fly.

Debuting in 1970, the 454 cubic-inch V8 stood decisively at the top of the bloodied hill of the horsepower wars, delivering 450 horsepower and 500 pound-feet of torque in the LS6-spec 1970 Chevelle, and (almost) 465 horsepower and 490 pound-feet of torque in the LS7-equipped 1970 Corvette that was never actually sold to the public. Still, the big-block 454 was a motor city force like no other.

A part of the Gen IV group of engines lovingly called “the rat motor”, the 454 was an evolution of its smaller sibling. In this case, its blueprints were taken from GM’s 427 cubic-inch V8, just stroked out to a larger 4 inches. But because it arrived so late to the game (1970), it wasn’t long before GM slowly began removing it from passenger car option lists. And by the late 1970s, it was a truck and SUV-only engine.

Production continued, though, and when the new Gen V big-block rolled around in 1991, the 454 was worse for wear, maxing out at a factory-rated 230 horsepower. Five years later, the Gen VI was introduced (1996), and the 454 was back, this time called the Vortec 7400, or “L29” for the nerds out there. Power was up, but not by much. About 290 horsepower was all it had to its name, and by 2001, the 454 was gone for good, replaced by none other than that darn Vortec 8100.