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GMC 454ci (1973–1978) specs: 454 ci (7.4L) 8-cylinder, 4.251 x 4.00 in (108 x 101.6 mm) bore and stroke, 8:1 compression. Rated 205 hp, 1973–1978. OHV.
The GMC 454ci (1973–1978) is oversquare — the 4.251" bore exceeds the 4" stroke by 6.3% — a layout that favors airflow and RPM over leverage at the crank. The 4" stroke puts mean piston speed at 4,000 ft/min around 6,000 RPM, which is where a production bottom end is generally considered at its limit. A rod ratio of 1.534 is short — higher piston acceleration and more side-load, typical of stroker combinations and a reason to watch piston speed closely. Each of the 8 cylinders displaces 56.8 ci (930 cc).
8:1 on iron heads is low by modern standards and generally happy on regular pump fuel.
It is one of 3 engines in the GMC 454ci family, all of them 454 ci — the differences between them are in compression, heads and rating, not displacement. 6 factory variants share these dimensions, rated at 205 hp across 1973–1978.
| Displacement | 454 ci / 7.4 L |
|---|---|
| Bore | 4.251" |
| Stroke | 4" |
| Cylinders | 8 |
| Configuration | V8 |
| Compression ratio | 8:1 |
| Rod length | 6.136" |
| Rod ratio | 1.534 |
| Bore/stroke ratio | 1.063 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Firing order | 1-8-4-3-6-5-7-2 |
| Advertised HP | 205 hp |
| Years | 1973–1978 |
| Year | Version | HP @ rpm | Torque @ rpm | Comp. | Duration int / exh | Valve lift int / exh | LSA |
|---|---|---|---|---|---|---|---|
| 1978 | net | 205 @ 3600 | 335 lb-ft @ 2800 | 8:1 | 300° / 314° | — | 116° |
Factory specification sheet. Durations are the factory's advertised figures at the basis printed on the sheet, not duration at .050" lift; lobe separation is calculated from the printed valve timing.
| Bore/stroke character | 1.063 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 4,000 ft/min — in the range typical of performance street engines |
| Rod ratio | 1.534 — short — more side loading and piston dwell at TDC, typical of stroker combinations |
| Displacement per cylinder | 56.8 ci |
| Static compression | 8:1 — low by modern standards, generally happy on regular pump fuel |
Each link opens the calculator with this engine's specs already filled in.
These records share identical bore, stroke, displacement and compression. They differ by model year and factory power rating.
| Year | Advertised HP | Code |
|---|---|---|
| 1973 | — | — |
| 1974 | — | — |
| 1975 | — | — |
| 1976 | — | — |
| 1977 | — | — |
| 1978 | 205 hp | — |