The switch occurred in the late 1980s, around 1987, when GM began widely using center-bolt valve covers on SBCs. This design change affected how valve covers were fastened and sealed, and it remains common on later small-block Chevy engines.
Understanding Center-Bolt Valve Covers
Center-bolt valve covers are secured with bolts along the centerline of the cover rather than around the entire edge. Proponents say the design can improve gasket sealing and simplify gasket changes, especially when engines feature modern heads or intake configurations.
Timeline: When did SBCs switch? (Key milestones)
The following timeline highlights when center-bolt valve covers started appearing on common SBC platforms and when they became widespread in production vehicles.
- Late 1980s: Center-bolt covers begin appearing on production SBCs in GM cars and light trucks.
- 1987–1990: Widespread adoption in many 305/350 small-blocks used in passenger cars, trucks, and heavy-duty applications.
- 1990s: Center-bolt design becomes standard for many GM service parts and crate engines based on the Gen I SBC platform.
Concluding note: While the center-bolt design became common in the late 1980s and persisted through the 1990s, not every SBC model adopted it at the exact same time. Some early 1987–1988 vehicles and certain export or specialty engines retained perimeter bolts for a period, and aftermarket center-bolt covers have been widely available since the design’s introduction.
How to identify a center-bolt SBC valve cover
Center-bolt covers can be identified by bolts that run along the cover’s centerline and by the absence of the traditional perimeter bolt pattern. They may also feature raised lettering or a stamped GM logo. If uncertain, check the valve-cover part number or compare with era-specific service manuals.
In short, the late 1980s marked the transition for many SBCs toward center-bolt valve covers, with broad adoption by the early 1990s. Timing can vary by model and production line, but 1987 is widely cited as the turning point.
Summary: The GM small-block Chevy generally moved to center-bolt valve covers in the late 1980s, around 1987, with widespread use through the 1990s. Variations existed by model and application, but the late '80s is the commonly cited turning point.