Bubic Big Block Case Study

Inside The 455 Cubic Inch Big Block from General Motors

Everything You Wanted to Know About the 455 Big Block

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'll also make an attempt to 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.
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. 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
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. They 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 [hot rod] 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