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GMC LG3 specs: 305 ci (5.0L) 8-cylinder, 3.736 x 3.48 in (94.9 x 88.4 mm) bore and stroke. Built 1977–1978. Used in the Chevrolet Camaro and Chevrolet Monza.
The GMC Small Block Chevy (LG3) is oversquare — the 3.736" bore exceeds the 3.4799" stroke by 7.4% — a layout that favors airflow and RPM over leverage at the crank. The 3.4799" stroke puts mean piston speed at 4,000 ft/min around 6,900 RPM, which is where a production bottom end is generally considered at its limit. A rod ratio of 1.638 is in the range most production engines fall in. Each of the 8 cylinders displaces 38.1 ci (625 cc).
It is one of 27 engines in the Small Block Chevy family, sitting between the 265 ci and 400 ci members. 2 factory variants share these dimensions across 1977–1978.
| Displacement | 305 ci / 5 L |
|---|---|
| Bore | 3.736" |
| Stroke | 3.4799" |
| Cylinders | 8 |
| Configuration | V8 |
| Compression ratio | 8.4–8.5:1 (published figures vary) |
| Rod length | 5.7" |
| Rod ratio | 1.638 |
| Bore/stroke ratio | 1.074 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Firing order | 1-8-4-3-6-5-7-2 |
| Years | 1977–1978 |
| Bore/stroke character | 1.074 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,480 ft/min — conservative for a street engine |
| Rod ratio | 1.638 — moderate — the range most production V8s fall in |
| Displacement per cylinder | 38.1 ci |
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 |
|---|---|---|
| 1977 | — | LG3 |
| 1978 | — | LG3 |
23 factory vehicles, 1976–1979. Each year opens that model's engine table.