Inside The 455 Cubic Inch Big Block from General Motors

455 Buick Wildcat Engine
455 Buick Wildcat Engine. Photo by Mark Gittelman

There's no question that 455 cubic inches of displacement equals a big motor. Nevertheless, this giant engine from the General is a little mysterious. In the beginning you would find them in Oldsmobile Motor Division products. As time went on you started seeing this exact displacement under the bonnet of Buicks and performance models from the Pontiac Motor Division.

Here we'll dig into the history of the record torque producing big block.

We will also uncover the difference between a 455 SD (Super Duty) and a 455 HO (High Output). Discover if the Buick, Pontiac or Oldsmobile engine has an advantage over the other. Finally, learn how the 455 benefited during a time when GM's divisions took great pride in making their own engines.

The Oldsmobile 455 Version

Olds beat the other GM divisions to market with the first 455 Cubic Inch motor. In 1968 the engine found its way into Oldsmobile's premium luxury muscle car, the 442. They called it the Rocket 455 which became an excellent marketing tool. They based the engine off of the 425 CID found in the 1967 Toronado. The company actually retained the same size bore yet increased the stroke by altering the crankshaft.

The side effects of a longer stroke include a healthy increase in torque. The downside is the engine finds itself a little slower at gathering RPMs. Horsepower ratings from 1968 through 1970 remained in the 375 to 400 HP range.

At first the engines remained exclusive to the Toronado, Cutlass and 442's. After 1970 you'll also find them in the Olds Vista Cruiser Station Wagons, Delta 88's and even GMC motor homes.

Stage I Buick 455 Performance Engine

The Buick version of the 455 is actually quite different from the Oldsmobile version.

Instead of altering the stroke, Buick honed out the cylinders on the 430 CID Buick Wildcat engine. For this reason GM considered it a thin-walled big block. The advantage of this casting design is a significant drop in weight over the other 455 versions.

In fact, the engine actually weighed close to 150 pounds less than the legendary 454 big block that Chevy used. This weight reduction compensated for slightly lower horsepower output from the Buick version. They rated the standard issue 455 at 350 HP and the high performance stage I version at 360 HP.

This engine had a short run starting in 1970. In 1975 General Motors started using the same engines across the different divisions and platforms. This gave them better compliance control for the increasing government regulations regarding fuel economy and exhaust emissions. For this reason you often find an Oldsmobile 455 under the hood of a 1975 or later Buick model.

The Pontiac version of the 455

In 1966 Pontiac really didn't have a small block engine. In an effort to keep things simple Pontiac designed all their V-8 engines around the same casting. Even the small displacement 326 CID motor is considered a big block. Therefore, the 389 Tri-power Trophy engine is also based off of the 326 block casting.

Fast forwarding to 1967 Pontiac altered the bore and stroke to produce the 400. This is the same year that Pontiac used the HO (High Output) to distinguish their engine from the Oldsmobile Rocket version and the Buick Wildcat engines. When 1970 rolled around, Pontiac offered their largest displacement in the company's history. Although you could still get a 400, you could also get 455 HO.

The Difference between a 455 HO and the 455 SD

The 455 HO is a bored out version of the Pontiac 400 HO. In 1970 Pontiac increased the displacement in an attempt to make up for reduced compression required by new government regulations. Engineers did their best to squeeze out as much horsepower as they could. They used the HO moniker to counteract the perception of lost performance. Meanwhile Pontiac assembled a special team to provide a permanent solution to the problem.

The team is asked to design a 455 that could retain performance while meeting the stricter standards. The result launched in 1973 as the Super Duty 455. The SD engine is different in so many ways over the standard HO version. I'll direct you to a technical article from Hotrod outlining the mechanical differences. Nevertheless, when the team finished the project, Pontiac provided one of the strongest and most powerful engines ever produced. This came at a time when most car companies abandoned performance in an effort to just survive.