General Motors Torque Specs
GM torque specs follow the engine family, not just the badge on the fender.
Start with the actual engine family. Chevrolet small block, Chevrolet W big block, Chevrolet Mark IV big block, Buick, Olds, Pontiac, Cadillac, and later GM engines are not one big bolt chart with different valve covers.
GM Big Block Torque Specs
Mark IV Family 396, 402, 427, and 454 big block Chevy
The familiar Chevrolet big block used through the muscle and smog eras. It needs its own page because Mark IV specs do not belong mixed with the earlier W engines.
Older GM Torque Specs
Early Chevrolet six-cylinder family
Old Chevrolet sixes are simple, but old does not mean universal. Thread condition, fastener length, gasket type, and exact engine family still matter.
Postwar Chevrolet six-cylinder family
Postwar Chevrolet six-cylinder torque specs belong with the engine family, not with later small block habits or generic inline-six guesses.
What’s Different
- GM reused familiar displacements across different engine families. Same cubic inches does not mean same architecture, same bolts, or same torque behavior.
- Chevrolet small block, W big block, and Mark IV big block engines are separate families. Do not use one page as a shortcut for another.
- Chevrolet W big blocks and Mark IV big blocks are both big blocks in casual conversation, but they are not the same engine family.
- Chevrolet small blocks are common enough to make people careless. Vortec heads, 400 blocks, main-cap variations, and replacement hardware can still change the job.
- Older GM-family engines may use thread sizes, pitches, and hardware that do not match later habits. Check the fastener before trusting the torque wrench.
- GM swaps are everywhere. The torque spec follows the engine family and the part with the threads, not the badge on the vehicle.
- Dirty threads, wrong bolt length, damaged holes, mixed hardware, and bottomed fasteners can make a torque reading lie.
- Most GM torque mistakes start with the same lazy thought: “It’s all basically the same.” No, it isn’t.
Parting Shot
The badge gets you close.
The engine family gets you correct.
If you tighten by assumption, GM gives you plenty of ways to be wrong.