The ＂Leaning＂ 6-Cylinder That OUTLIVED Detroit’s Greatest V8s

There's an engine sitting in barns, combines, old darts, and the occasional forklift that outlasted the 426 Hemi, the 446 Pack, the Boss 429, and pretty much every other V8 that ever made the cover of a car magazine. It was not supposed to be special. It was not even supposed to be tilted. But tilt it they did, 30 degrees off vertical, and that one decision accidentally created one of the most overbuilt, overachieving, and flat-out unkillable engines in American automotive history. This is the story of the Chrysler Slant 6. To understand why this engine exists at all, go back to the late 1950s and understand just how badly Chrysler needed a win. Their six-cylinder situation was, to put it charitably, a disaster. Chrysler had been running some variation of the same L-head flathead in Line 6 since 1925. The automotive version finally limped off the line in 1959, which means that by the time it retired, this engine had been in continuous service for over three decades. By the late 1950s, with a new era of compact cars coming, it was painfully clear the old flathead was not going to cut it anymore. The big three were all scrambling to build compact cars in response to the growing import threat, particularly the Volkswagen Beetle, which was quietly eating American market share while Detroit was not paying attention. Ford was cooking up the Falcon. Chevrolet was doing something genuinely weird with a rear-engined, air-cooled design that would become the Corvair. And Chrysler needed their own answer, a car they were calling internally the Q-Car, which would eventually reach the public as the Plymouth Valiant. The problem was they had nothing to put in it. The old flathead was too heavy, too tall, and too long. It was a complete non-starter. So in 1957, Chrysler commissioned a clean-sheet six-cylinder engine. The man who led that program was Willem Wurtmann, who would eventually become Chrysler's chief engine designer, working alongside Robert S. Rary, who had already proven himself leading the B&R BV8 project. These were not junior engineers handed a throwaway assignment. What they ran into almost immediately was a packaging problem. A conventional upright inline six was too tall for the Valiant's planned low hood line, and the standard front-mounted water pump made the engine too long for the compact engine bay. Lead designer Fred Rose and design supervisor Ray Latham had the solution. They moved the water pump off the front, mounted it laterally to shorten the overall length, and tilted the whole block 30 degrees to the passenger side. Simple, elegant, and as it turned out, accidentally brilliant. The first iron block 170 cubic inch prototype hit the dyno in November of 1958, just months after the program was approved. Two weeks later, the 225 was on the dyno behind it. Chrysler's engineers had just built something genuinely new. They did not fully know it yet. Now, Plymouth's marketing team initially called it the 30D Economy 6, which is about as exciting as naming a dog dog. It referred to the 30 degree cylinder bank angle, and it did not stick. What did stick was the name from Chrysler's own press releases right from the start, Slant 6, because that is exactly what it looked like. An engine that had tipped over to one side and just stayed there. But here is what nobody fully appreciated in 1960. The tilt was not just a packaging solution. It accidentally unlocked a set of engineering advantages that conventional inline 6s of that era simply could not match. When you lay an inline 6 over on its side, you create space in the engine bay that does not exist in a conventional upright installation. A Chrysler engine designer named John Hurst came up with the concept, fine-tuned by John Platner and Don Moore. The result was a sinuous curved intake manifold that became known around Chrysler as the Bunch of Bananas, and the nickname was earned. Runners for cylinders 1 and 6 were approximately equal length, 2 and 5 equal, 3 and 4 equal. That symmetry meant each cylinder got essentially the same air fuel charge at the same time, which is exactly what you want for consistent combustion and smooth power delivery. Competitive designs from GM and Ford at the same price point had some cylinders sharing runners, others with sharp bends, others with dramatically different lengths. The slant 6's manifold was genuinely better engineered. The block itself was built with a deep skirt design, with the crankshaft axis sitting well above the oil pan rails, the same structural philosophy Chrysler used in the second generation Hemi 5.8. The four main bearings were sized identically to the five bearing Hemi mains. The crankshaft was forged steel. The top piston ring was chrome-plated, solid lifters throughout. These were not the choices you make for a throwaway economy engine. When the 225 cubic inch version launched for 1960, it made 145 horsepower at 4,000 revolutions per minute and 215 pound-feet of torque at 2,800 revolutions per minute on gross figures. The undersquared geometry, a 4.125-inch stroke against a 3.40-inch bore, prioritized low revolutions per minute torque over top-end power, which made it strong, flexible, and easy to live with. Consumer Reports consistently praised it for outperforming equivalent GM and Ford 6's in both speed and economy. GM even ran their own internal test on a 1961 225 and reportedly found 126.5 horsepower at 3,800 revolutions per minute and 210.7 pound-feet of torque at just 1,600 revolutions per minute under controlled conditions. That last number is the telling one. Torque at 1,600 revolutions per minute. This engine pulled hard from almost nothing. Between 1961 and 1963, Chrysler experimented with an aluminum block version of the 225, producing over 50,000 of them. The cast in iron cylinder liners had a tendency to separate from the aluminum casting. Chrysler quietly shelved the aluminum block by 1963 and never looked back. The iron block was better in every way that mattered, and the iron block is what the legend was built on. So by the end of 1960, Chrysler had an engine that was mechanically overbuilt, breathed better than anything in its class, and made more torque than the competition at virtually every engine speed. What they needed next was a moment, and NASCAR was about to hand them one. Bill France sanctioned the Cannonball Compact Car Division, a new race class for the incoming domestic compacts. All three manufacturers accepted, and all three developed performance packages to homologate their cars. Chrysler handed the program to a young engineer named Tom Hoover. It was his first major performance assignment at the company, and he treated it like the most important engine project on earth. He was right to, because the work he did on that six-cylinder launched him directly into leading development of the 426 Hemi. But in 1960, Hoover's job was simpler. Take the slant six and make it embarrass the competition on a racetrack. What came out of that program was the Hyperpack. It was never a factory installation. It was sold over the parts counter at Chrysler dealers from day one. For approximately $430, roughly $4,300 in today's money, you got a long-runner aluminum intake manifold that was only physically possible because the engine was tilted, a Carter AFB4 barrel carburetor, dual cast iron exhaust headers with the front three and rear three cylinders routed separately, a camshaft with 276 degrees of duration, and heavy-duty valve springs. Full race versions added domed pistons, pushing compression up to 10.5 to 1. The dealer Hyperpack 170 was rated at 148 horsepower. The 225 version came in at 196 horsepower, and that number is worth sitting with for a second because the base two-barrel, 273-cubic-inch V8 Chrysler introduced in 1964 debuted at only 180 horsepower. The Economy 6 outrated the new small-block V8 by 16 Ponies. The racing debut came January 31, 1960 at Daytona, two races same day. Race one was a 10-lap road course at 3.81 miles per lap. Valiant swept the top seven finishing positions. Marvin Panch won, averaging 88.134 miles per hour. Race two was 20 laps on the high-speed oval. A multi-car crash on lap four took out four Valiants, including a young Richard Petty, who by his own admission had never run a road course in his life and had already crashed out of the first race on lap two. Panch had been delayed in the pits at the start and avoided the carnage entirely. He charged from the back of the field, caught the leaders, won the race, and averaged 122.282 miles per hour from a brick-shaped compact on 170 cubic inches. The remaining Valiants finished 1-2-3. The Top Falcon came in fourth. The Corvair was not close. The series ran one final time in 1961, with Lee Petty winning the road course. After two rounds of complete and total domination, NASCAR pulled the plug on the compact class. The official story was that it was not compelling television. Sure, I would also wager that Ford and GM were not exactly lobbying Bill France to run it back after watching their brand new compacts get embarrassed on live national TV. Either way, the Hyperpack program was discontinued. The engine went back to a single-barrel carburetor, but the nickname the racing had earned it stuck forever. The Leaning Tower of Power, and the engine was about to prove you did not need a racetrack to become a legend. Through the 1960s and into the 1970s, the Slant Six settled into the role it would play for the rest of its life, the sensible choice. It became the backbone of Chrysler's Abati platform. It was the engine in the Dart your neighbor drove to work every day, the Valiant your aunt bought because it was cheap to insure, the Duster sitting in high school parking lots next to the cars everyone actually wanted, while the 340, the 440, and the 426 Hemi were collecting magazine covers and quarter-mile trophies. The Slant Six was collecting miles. Quietly. Relentlessly. Without complaint. It wasn't just powering cars, either. Agricultural equipment manufacturers licensed it for combines and windrowers, John Deere Model 800 and Model 830 swathers, the Hestan 6400 Case 1H mowers, industrial forklifts, marine applications of every description. Chrysler developed dedicated industrial variants with two-row timing chains, chrome upper piston rings, stellite-coated exhaust valves, and high-volume oil pumps built specifically for continuous duty cycles that would destroy a lesser engine. There are people who spent years looking at a Slant Six in a piece of farm equipment with absolutely no idea what they were looking at. That's how far this engine spread. Then the muscle car era ended. Not gradually. Abruptly. Insurance rates spiked, emissions regulations bit down hard, and the engines that had spent the better part of a decade making the Slant Six look invisible started disappearing from the order sheets. This is where the title of this video earns its keep. The Boss 429 Ford's hand-built tunnelport racing engine lasted exactly one model year from 1969 to 1970. One year. The 426 Hemi, the most famous performance engine Chrysler ever built, the engine that dominated NASCAR and defined what a muscle car could be, was last offered in a passenger car in 1971. Eight years. The 446 pack was dead by 1971. Pontiac's 455 HO was gone by 1972. Chevy's LS6 454 was neutered almost immediately by emissions regulations and quietly shelved. Chrysler's own 340 small block, the engine that gave the Duster 340 its entire identity, was discontinued after 1973. The Slant Six was on its 14th year of production when the 340 died, 14th. And it kept going. 1974, 1975, 1976. Still on the line, still in the darts and valeras, rolling off the assembly floor, while the engines on bedroom posters all over America were turning into museum pieces. By 1976, the emissions stranglehold had taken a real toll. The 225 that made 145 gross horsepower in 1960 was now rated at 100 net, a 31% power loss from catalytic converters, EGR valves, and air injection pumps all fighting each other under the hood. But Chrysler found a way to make the Slant Six useful in a completely different direction. The Feather Duster was a $51 option package on the Plymouth Duster. It replaced hood and trunk bracing, bumper reinforcements, and the intake manifold with aluminum equivalents, saving 187 pounds off the curb weight. And it paired a specially tuned 225 with a 2.94 to one rear axle and a four-speed overdrive manual transmission. The EPA rated it at 36 miles per gallon on the highway and 24 in the city. That was the highest EPA highway rating ever recorded for an American six-cylinder compact at the time. The most frugal performance engine of the muscle car era had just become the most fuel-efficient compact in America. The 426 Hemi got eight years in passenger cars. The Slant Six was on its 16th year, and it wasn't done yet. By 1977, Chrysler knew the Slant Six needed help. The single-barrel carburetor, strangled to meet emission standards, was making the engine feel hesitant, off-idle, rough at cruise, and generally unpleasant in a way the earlier versions never had been. The solution was characteristically simple. A valve engineer and two road test mechanics, three people total, developed what became known as the Super Six package. A Carter BBD two-barrel carburetor borrowed from the 318 V8, a matching intake manifold, and revised distributor advance curves. No exotic engineering, no expensive redesign. Horsepower bumped to approximately 110 net, and the drivability issues largely went away. As Pete Hagenboek, the retired head of Chrysler engine tuning, later confirmed, most of the benefit came simply from fitting a more appropriate carburetor, something even small European and Japanese engines had been running for years while American manufacturers stuck stubbornly to single barrels. Chrysler did make the idle mixture screws deliberately inaccessible so owners could not tune the carb themselves. That was not an oversight. That was the emissions compliance department. The attempts to modernize grew more ambitious from there and less successful. A turbodiesel prototype was developed. An overhead cam version had actually been built by a Chrysler engineer named Jim Grundy back in 1971, installed in a Dart and driven regularly, but Grundy could not generate institutional interest, sold the car in 1973, and it turned up at a Michigan State University engine lab in 1992. For 1981, hydraulic valve lifters finally replaced the solid lifters that had been in continuous use since 1960. 21 years of solid lifters ended not by performance philosophy, but by tighter emissions tolerance requirements on the assembly line. That same year, electronic mixture control arrived on the carburetor, which sounds like progress and largely was not. Vacuum leaks multiplied. Warning lights started coming on for reasons nobody could fully explain. The engine celebrated for its simplicity was being buried under layers of hardware it was never designed to carry. Passenger car production ended in 1983. The last domestic trucks left the line in 1987. Marine and industrial applications ran until 1991, 31 years after the first prototype fired up on a Chrysler dyno in November of 1958. It didn't die because it wore out. It stopped because it was too long and too fundamentally rear-drive oriented to survive Chrysler's shift to front-wheel drive platforms, and because the 2.2 liter four-cylinder replacing it was shorter, lighter, and easier to certify under the regulations that had been slowly strangling the six for over a decade. The slant six didn't lose a fight, it just ran out of road. The slant six never really left. The durability folklore alone could darts with 300,000 miles on original, never rebuilt engines. A 225 pulled from a wrecked Valiant and bolted into a lumber mill saw, where it ran 10 hours a day for over 12 years before anyone thought to replace it. And then there is the story told in every slant six form you will ever find. The teenager who drained the oil from his mother's duster trying to kill the engine so he could justify swapping in a V8. He drove it around town for days, drove it to school, the engine never knocked, the oil went back in. That story exists in about 40 different versions involving 40 different people, and I believe every single one of them. The hot rod community never let it go either. The deep skirt block and the forged crankshaft on engines made before 1976 anyway, can handle a serious amount of boost. Mopar Magazine documented a home-built, low-budget turbo slant six running consistent 12 second quarter mile times at the drag strip. 12 seconds from an engine that came out of a taxi cab. The aftermarket never dried up completely. Wyan four barrel intakes, Aussie speed manifolds, headers. You can still build one today. People do. And here is where we come back to the title, because this is the part that deserves to be said out loud and slowly. The Boss 429 lasted one year in production. One. The 426 Hemi lasted eight years in passenger cars. The 440 six-pack lasted seven. The LS6 454 was neutered after a single season at full strength. The 428 Cobra Jet was gone by 1971. Chrysler's own 340 was dead after 1973. These were the engines on bedroom posters. These were the engines that made the muscle car era what it was, that boys grew up dreaming about, that journalists ran out of superlatives trying to describe. The slant six, the economy engine, the taxi cab engine, the farm equipment engine, the engine tilted 30 degrees because an engineer needed somewhere to put the in passenger cars until 1983. It ran in trucks until 1987. It ran in marine and industrial production until 1991. 31 years of continuous production. It outlived every single one of those engines by more than a decade. And when it finally stopped, it was not because it failed. It was not because it wore out. It was not because anyone found something more reliable to replace it with. It stopped because the world changed around it. The engine itself never gave anyone a reason to stop building it. That is what outlived actually means. Not just longer, but undefeated. The leaning tower of power never fell down. They just eventually stopped stacking bricks. Let me know in the comments whether you have ever owned one of these or whether you have ever tried to kill one and failed. I have a feeling there are a lot of those stories out there. I hope you all enjoyed another episode of The Car Archives. If you did, a like and a subscribe go a long way. I will see you all in the next one, enthusiasts.