The Chevy 454 CID big block engine (BBC), introduced in 1970, was a popular engine for both heavy-duty truck and performance automobile applications. Aftermarket aluminum heads are common performance upgrades for the engine. While no longer in production (except in the aftermarket), this engine underwent several slight design changes over the years. The "Gen 5" 454 big block Chevy uses the same general cylinder head design as earlier and later designs, but one important change presents a possible problem when adapting/upgrading cylinder heads.
The "Gen 5" design was introduced in 1991. It was subsequently replaced by an improved Gen 6 version in 1995 due to problems with parts interchangeability and other shortcomings. The coolant passages in the Gen 5 block were slightly changed from earlier "Mark IV" engines, and this presented the possibility of coolant leaks into the lifter valley of the engine when more desirable Mark IV-style cylinder heads were used on the Gen 5 block. General Motors engineers revisited the design in 1995 and corrected this problem, among others, with the "Gen 6" 454. Fortunately, however, aftermarket parts manufacturers have incorporated extra material into their aluminum cylinder head castings that allow them to be used universally across the three block generations/designs.
Cylinder heads are most often designated by the size of their intake port volume. For example, anywhere from 270 cc to 360 cc or more. Heads are also rated/measured in cubic feet per minute (CFM) of airflow. More important, however, is the shape of the port and the quality of the airflow. Good port velocity produces torque which is, in turn, translated into horsepower at high RPM.
The 454 BBC is currently considered a "small" engine when compared to other BBCs configured with aftermarket parts combinations. As such, a 454 will not have the airflow requirements a 550 to 600-plus cubic inch displacement (CID) engine will. Correct air velocity is one of the most important factors in choosing an aluminum head for the 454. The intended usage of the engine dictates which head should be used. A "street-driven" or marine 454 will have much lower airflow needs than a 454 that is used only in competition, such as from 5000 to 7500-plus RPM.
GM factory production BBC heads typically had intake runner volumes of 230 to 270 cc, with the larger port volume heads being used in their performance versions. Aftermarket heads have improved, larger ports and quality of airflow but must be properly matched to the camshaft and intake/exhaust systems for best results. Several aftermarket vendors offer suitable choices.
For an application that is intended for higher output but will still be used on the street, a cylinder head such as the Brodix Race-Rite 270 cc runner oval port aluminum head or the GM Performance Parts 290 cc runner head can be a good choice. Heads such as the Airflow Research (AFR) 305 cc Magnum BBC Cylinder Head could be the upper end of an engine that still is used in stop-and-go driving situations and still be somewhat responsive at low engine speeds.
For a competition-only 454, heads with 300 to 325 cc intake runner volumes may be the limit without requiring more displacement. Examples of these heads would be the Racing Head Service (RHS) Pro Action Big Block 320 cc runner heads or Dart Pro 1 heads with 325 cc intake ports.
Avoid the temptation of selecting a cylinder head that is "too big". When faced with similar head choices, heads with slightly smaller ports typically provide better results.
When upgrading cylinder heads, be certain to check for interference from domed pistons and/or altered spark plug locations.
