Unlike most other car makers at the time, Buick had been using a valve-in-head/OHV overhead valve reverse-flow cylinder head design or I-head since their inception and continued this practice in their straight-eight designs.

The engine was sold in different displacements depending on the model of car and the year and was constructed upon two distinct (possibly more) block castings.

The engine block in the smaller displacement versions internally resembled the 1937-53 inline Chevrolet 216, 235 & 261" straight six (the combustion chamber design was quite different), albeit with additional cylinders.

The large block version (320 cid and 345 cid; used in large-chassis models such as the Roadmaster) was considerably heavier and this weight adversely affected vehicle performance and handling.

All other lines using the same basic chassis received the new V8 322 cu in (5.3 L) Fireball.