Are They All The Same Engine?

For many gearheads, the year 1970 represents the peak of the muscle car era — or at least the peak of the first muscle car era. A big part of what conspired to make 1970 special is that to remain competitive against brands like Chrysler with its 440 Magnum, 440 Six Pack, and 426 Hemi, General Motors dropped its 400 cubic-inch size limit for engines in the midsize cars on which GM’s muscle cars were based.

Perhaps most famously, this rule change launched Chevy’s 454 cubic inch Chevelle SS in two flavors: a 360 horsepower LS5 or the ground-pounding LS6 with 450 horsepower. Sooner than later, these high-compression big-blocks would be hampered by performance-killing events like an oil crisis, unleaded fuel, skyrocketing insurance rates, and primitive emissions controls, but it was glorious while it lasted.

Not to be outdone, Oldsmobile, Buick, and Pontiac all upped the ante from 400 to 455 cubic inches for their Cutlass 442, Gran Sport, and GTO muscle cars, respectively. Considering the modern practice of using “corporate” engines across multiple sub-brands, one might assume that these three 455 powerplants are the same, but that’s not the case. All three engines were developed independently, with no shared architecture between them besides the happenstance of reaching the same magic displacement number. Additionally, each arrives at its 455 cubes via a unique bore and stroke measurement. 

Oldsmobile, the company founded by Randsom Olds in 1897, released its second-generation pushrod V8 engine design in 1964 with a 330 cubic inch displacement. Within a few years, that design had expanded into the 455. Oldsmobile achieved its 455 cubic inches by increasing the stroke — the distance a piston travels inside its cylinder — versus the smaller 425 cubic-inch iteration. The resultant taller deck height made the Olds 455 a true big-block, with a 4.125-inch bore and aforementioned 4.250-inch stroke.

This engine was available in large vehicles like full-size sedans, station wagons, and limited-edition Hurst muscle cars as early as 1968, but enthusiasts will best remember the variant in the 1970s Cutlass-based 442 (short for four barrel carb, four-speed manual, dual exhaust) with W-30 performance package. That combination made 370 horsepower and a stump-pulling 500 lb-ft of torque. Interestingly, the chunky 455 with its wide intake manifold also appeared in the Oldsmobile Toronado, an early front-wheel drive GM car. 

That same “Unitized Power Package” that pulled the FWD Tornado would also find an unlikely home inside the futuristic GMC Motorhome, the only factory-produced motorhome ever offered by Detroit’s Big Three. If the Olds 455 has an Achilles heel, it’s surely the small oil return passages, which starve the engine for oil at high rpm. While okay for street driving, this flaw gave the Olds 455 something of a bad reputation for use in drag racing and other high-rpm motorsports unless specially modified. 

Much like Buick’s turbocharged, intercooled Grand National and nondescript Regal T-Type in the 1980s, the brand’s Gran Sport muscle car was something of a sleeper. Buick might be a name that’s typically associated with retirement communities and golf courses, but the 455-powered Gran Sport and GSX of 1970 were real hell raisers, albeit in a classy outer wrapper. Buick’s take on the 455 has its roots in the new-for-1967 400 and 430 cubic inch engines. Unlike some other GM brands’ 455s, Buick opted to give its largest displacement engine a big bore of 4.3125 inches rather than increasing the stroke, which remained at 3.90 inches.

Buick’s 455 powered its share of boring land yachts to be sure, but the brand also released a specially tuned “Stage 1” option which was available in its 1970 muscle cars like the Gran Sport. Specifically, the Stage 1 455 had a higher compression ratio, performance cam, and larger valves. The result was 360 horsepower and 510 lb-ft of torque. At a time when other manufacturers were prone to exaggerating their engine’s horsepower ratings to impress consumers, the Stage 1 Buick 455 was actually thought to be underrated from the factory. In January 1970, Motor Trend made a 13.38 second pass in the standing quarter mile with a four-speed manual-equipped Stage 1 Gran Sport. Although that’s nothing special by modern standards, the magazine crowned the GS the “fastest muscle car it ever tested,” as reported by Hagerty. 

Pontiac’s first foray into the realm of pushrod V8 engines was way back in 1955 with a modest 287 cubic-inch mill. Remarkably, that same engine would morph into the brand’s torque-monster 455 over the years. That means, unlike the other brands in this article, it isn’t technically a big-block. Pontiac’s take on the 455 features a 4.1525-inch bore, 4.21-inch stroke, and was available with either two-bolt or four-bolt main bearing caps, with the latter designated “High Output” (HO). 

When even HO isn’t strong enough, buyers could opt for the Super Duty variation of the 455 which featured a beefed-up engine block with extra material added for strength, plus forged pistons and connecting rods. In 1970, Pontiac made 4,146 GTO muscle cars with the top-dog 455 cubic inch powerplant, which made 360 horsepower and 500 lb-ft of torque. While that’s certainly respectable, it’s worth noting that little to no power was gained versus the smaller 400 cubic inch mill despite the extra 55 cubes, so what happened? The 400 cube V8 had available Ram Air III and Ram Air IV equipment, including better-breathing cylinder heads. 

The 1970 455 was supposed to get the Ram Air treatment as well, but Pontiac backed away at the last minute, correctly citing upcoming fuel economy and emissions regulations as a deal-killer. In its final year of production, Pontiac’s 455 made just 200 horsepower in the screaming chicken-adorned 1976 Trans-Am. Still, that was enough to make it one of the fastest cars on the market in a Malaise-era America.