Evandro Klen/ShutterstockStraight-6 engines earned their reputation for silky smoothness the traditional way — no overly complex balance shafts or exotic counterweights required, just six cylinders firing in perfect natural harmony. However, since the cylinders sit in a straight line, the tradeoff is length, That packaging headache is a unique disadvantage of the inline-6, which is why most automakers have kept their straight-6s fairly modest in size.But a handful of manufacturers ignored that logic, chasing torque, cruising comfort, or occasionally straight-up power, with inline-6s that grew to absurd proportions. Multiple engines on this list displace more than 11 liters — bigger than most V12s ever put in a car. That's the kind of number that seems impossible for a layout best known for being refined and about as far from "big-block" as you can get.These giants span nearly a century of automaking, built by manufacturers on both sides of the Atlantic. Here's a look at five of the largest ever made, ranked by displacement from smallest to largest.AdvertisementAdvertisementRead more: What Are The Rarest Cars Featured On Jay Leno's Garage?5. Bentley 8 Litre (1930–1932)Dmitry Eagle Orlov/ShutterstockBentley's largest engine arrived at the worst possible moment. W.O. Bentley built the 8 Litre to go head-to-head with Rolls-Royce's Phantom in the ultra-luxury market, carrying a displacement of 7,983 cc — nearly 8 liters, and easily the biggest six-cylinder unit the company ever fitted to a road car.It was the British automaker's philosophy in action: Chasing more power through added displacement, to the point of opposing supercharging on principle, even as Bentley's most famous, yet underwhelming, race car of the era went a completely different route with a blower strapped to its 4.5-liter. With 220 horsepower on tap, the 8 Litre could reach 100 mph despite the weight of its formal coachwork.Engineers fought the extra bulk with material choice rather than cutting displacement. The crankcase was cast in Elektron, a lightweight magnesium alloy, to keep the enlarged engine from adding even more mass to an already heavy chassis. Two chassis lengths were on offer, 144 or 156 inches. At the time, no British manufacturer was building anything on a longer chassis.AdvertisementAdvertisementBut timing undercut everything the engineering achieved. Production topped out at a mere 100 cars over the two years the model existed, a span that overlapped almost exactly with the start of the Great Depression. The luxury market's collapse left the company unable to continue independently, and control passed to Rolls-Royce in 1931.4. Locomobile Model 48 (1911–1929): 8.6 litersS.Candide/ShutterstockLocomobile, of Bridgeport, Connecticut, built its reputation on refusing to rush anything, and the Model 48 proved that philosophy in engine form. Andrew Riker's design made 70 horsepower from its 429 cubic inches when the car launched in 1911 — already well ahead of the "48" horsepower rating that gave the car its name, since that figure was a taxable rating based on bore and cylinder count, not actual output.Riker's engineering career didn't start with gasoline — by 1896, his electric roadsters were beating gasoline cars, years before he ever touched a T-head 6. That EV pedigree traces back to a teenage project: a homemade three-wheeled electric vehicle, built around the same era as some of the first practical electric cars anywhere in the world. By the end of the 1910s, the Model 48 block's capacity climbed to 525 cubic inches, or 8.6 liters. The bore stayed fixed at 4.5 inches while the stroke grew from its original 4.5 inches to 5.5, accounting for the displacement gain. Output followed a similar trajectory, with figures from the 1920s putting horsepower comfortably past the century mark.AdvertisementAdvertisementWhat set the Model 48 apart, though, wasn't size, but who bought it. Chewing-gum magnate William Wrigley and members of the wealthy Vanderbilt family kept them in their garages, alongside film director Cecil B. DeMille. The car stayed in production for an unusually long 18 years with its fundamental engineering barely touched, a rare feat for any car built before the Depression reshaped the American luxury market.3. Oldsmobile Limited (1910–1912): 11.58 litersYouTube/Exotic AffinityIf there's one luxurious American car brand whose demise enthusiasts still haven't fully made peace with nearly two decades later, it's Oldsmobile. And the 1910 Model Z Limited stands out, thanks to an engine that dwarfed almost everything else on the road.Company lore held that the Limited earned its name by outrunning the 20th Century Limited express train from Albany, New York to New York City, though the story traces back to a promotional painting Olds commissioned rather than a documented race. Whatever the truth of the legend, the car backing it up carried a 505-cubic-inch straight-6. In 1912, Oldsmobile went further. Engineers added over 200 cubic inches to the block, bringing total displacement to 707 cubic inches, or nearly 11.6 liters.That larger engine used a T-head layout, with each casting holding two cylinders rather than one, and measured 5 inches across the bore against a 6-inch stroke — without any corresponding gain in horsepower, which held at 60. Housing that much engine meant the frame now spanned 138 inches between the axles, sitting atop wheels that measured a full 42 inches.AdvertisementAdvertisementRarity only intensified as the model aged. By its final year, Oldsmobile built under 140 before shifting focus to smaller, cheaper cars. That scarcity still commands serious money — a 1911 Limited sold at auction for $5 million in September 2025, making the Limited the most expensive Oldsmobile ever sold at an auction.2. Peerless Model 60 (1912–1914): 13.5 litersAkrasia25/Wikimedia CommonsIn 1912, Cleveland automaker Peerless entered near the very top end of huge inline-6 engines with the Model 60. The car relied on a straight-6 architecture using the same T-head valve layout as the Pierce-Arrow Model 66 (which you'll find next in this list), reaching 824 cubic inches of displacement, or 13.5 liters. This was not surprising since Peerless, Pierce-Arrow, and Packard were known as the "Three P's" that battled each other to make the most luxurious aristocrat-mobiles. Packard would later push the format further, building some of the last production inline-8s. Pierce-Arrow and Peerless ended up so evenly matched on paper that displacement claims for their engines are frequently cited within a single cubic inch of one another, making the Model 60 a genuine co-holder of the largest-displacement record rather than a footnote to it. Each pair of its cylinders shared a single casting, with a 6-inch bore and 8-inch stroke. Fuel reached the engine through one central carburetor, and every cylinder relied on a pair of valves to manage that airflow.Peerless matched the ambition with exclusivity to match. A 1912 Model 60 cost buyers $6,000 new, and by 1914, production of the Model 60-Six Touring had shrunk to just 57 units. Car production at Peerless ended right around the Great Depression, but for a brief window, its straight-6 stood equal to Pierce-Arrow at the top of American engine displacement.1. Pierce-Arrow Model 66 (1910-1918): 13.52 litersJay Leno's Garage/YouTubePierce-Arrow's Model 66 remains the benchmark for engine excess, at least among straight-6s. Its T-head debuted in 1910 at 714 cubic inches, and 1913 brought a further increase, this time to 825 cubic inches — 13.52 liters, or about 4½ times bigger than Toyota's iconic 2JZ. Guinness recognizes this as the largest engine in a production car, although it's nowhere near the largest engines ever built.AdvertisementAdvertisementDespite the Model 66 engine's size, output actually stayed modest — by design. The engine's maximum speed sat at 1,500 rpm, and the extra displacement eventually pushed output to almost three-digit horsepower, trading outright speed for effortless low-end pulling power. Buffalo, New York-based Pierce-Arrow wasn't chasing lap times — it was building the ultimate American luxury car, and a straight-6 this size could haul a heavy chassis without ever feeling strained.Production of the Model 66 preached 1,250 cars before the run ended in 1918, riding on wheelbases as long as 147.5 inches to support the coachbuilt bodies fitted to the largest examples. Body styles ranged from open runabouts to formal seven-passenger touring cars, all built for a wealthy clientele who wanted their straight-6 felt as much as heard. Surviving examples today are prized as some of the most significant American Brass Era cars ever built, so much so that RM Sotheby's even named it "the Holy Grail" of the era.Want more like this? Join the Jalopnik newsletter to get the latest auto news sent straight to your inbox, and follow us or add us as a preferred search source on Google.Read the original article on Jalopnik.