The History Of The Oldsmobile 455: GM's 'Other' Big Block Muscle Car Monster

• February 23, 2021
• Story By
  Benjamin Hunting

Oldsmobile's name has long since disappeared from the modern automotive landscape, but this victim of GM's financial failures left an important, if often overlooked, legacy during the muscle car era. Overshadowed by the likes of Chevrolet and Pontiac, Oldsmobile delivered one of the mightiest, and most versatile big block engines of the period: the 455 V8.

What helped set the Oldsmobile 455—also known as the 'Rocket'—apart from the other large displacement eight-cylinder engines offered by General Motors was in the wide range of vehicles where it was available as an option. Not only did Oldsmobile stuff the 455 under the hood of the popular 442 muscle car, but it also made it available in the larger, family-oriented Delta 88 as well as the 98 luxury sedans, and even in the front-wheel drive Toronado (marking the General's first experiment with what would later come to be the industry's dominant drivetrain layout).

Dive into the Oldsmobile 455 big block's details, and it's easy to see why this V8 had such a broad appeal—and why it continues to present excellent value for hot rodders and classic car restorers alike.

All Torque, All The Time

Debuting in 1968, the 455 Rocket represented the second-generation eight-cylinder engine design offered by the brand, replacing the original Rocket that had pulled duty for 15 years. The 455 cubic inch version of the motor represented the largest on offer (with 400 and 425 cubic inch engines also available), and it featured a higher deck as compared to the small block V8 then in use by the brand.

The 455 delivered a longer stroke than the 425 (4.25 inches) while sharing the same bore (4.126 inches). As was common practice at the time, Oldsmobile manufactured a number of 455 variants, altering compression ratios, piston designs, and intakes depending on which application the motor was used for. Factory horsepower ratings ranged from 310 all the way up to 400 ponies, with 500 lb-ft the most common torque figure.

The Cutlass would benefit from the hottest versions of the 455, starting right out of the gate with 1968's Hurst/Olds, a 390hp special model with a more aggressive camshaft and carb setup. Just over 500 of these were built, but a slightly milder version of the same engine would continue in the car the following year.

A better-known and more common special edition 455 was the W30 package, which debuted in 1970 on the 442 edition of the Cutlass. Although it reported 20 less horsepower than the Hurst/Olds, it featured forged connecting rods, aluminum pistons, and a balanced rotating assembly. Again, camshaft specs (.475/475 lift) nudged the big block's personality into the red zone, and an aluminum intake was standard.

Sunsetting The Muscle Car Era

In 1971 the Oldsmobile 455 V8 would begin to fade from the high performance landscape. Compression would drop from 10.5:1 to 8.5:1 even in W30 package cars, and camshafts would slide back to the streetable side of the ledger. This knocked torque down to 460 lb-ft and horsepower to 350, both gross ratings. The 442 would carry in one form or another throughout the decade, but after 1973 its was a shadow of its former self, and by 1975 it couldn't even break the 200hp barrier (albeit judged by the less forgiving SAE net rating, which tested engine output fully-dressed with exhaust and accessories).

The 455 had been dropped by the Toronado in 1971, but General Motors was so pleased with the performance of its front-wheel drive 'Unitized Power Package' that it would live on until 1976 pulling the GMC Motorhome (which has itself become a classic).

It would also continue in the Vista Cruiser and Custom Cruiser station wagons, as well as the 88 and 98 sedans, but each of these was subjected to an even more crushing performance handicap than had been seen in the 442.

By the end of the decade, only a small number of 455 big blocks were still being built for industrial and commercial use.

Cheap And Easy Power 

Today, the Oldsmobile 455 is a popular alternative big block muscle car engine, particularly for owners who plan to use their cars exclusively on the street rather than regularly take them to the drag strip. Although small oil return passages make the 455 V8 a less-than-ideal option for continued high RPM use, these can be fixed with a larger oil pan and an oiling restriction system.

Perhaps the best part about choosing the Oldsmobile 455 for your project is its availability. With so many different cars featuring at least one version of the V8 over a period of nearly a decade, it's inexpensive to pick up a block to serve as a base. The engine responds well to camshaft upgrades, and of course low compression ratios from later engines can be improved through judicious piston selection. Parts available remains good, and it's become common to replace the factory rope rear main seal with a neoprene unit from Ford's 460 big block for improved reliability. With carefully-selected components and a little expertise, building a 500 horsepower version of the classic big block is well within most budgets.