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Pontiac L78 specs: 301 ci (4.9L) 8-cylinder, 4.002 x 3.01 in (101.7 x 76.5 mm) bore and stroke, 8.2:1 compression. Built 1978. Used in the Pontiac Grand Am.
The Pontiac 301ci (L78) is oversquare — the 4.002" bore exceeds the 3.01" stroke by 33.0% — a layout that favors airflow and RPM over leverage at the crank. The 3.01" stroke does not reach 4,000 ft/min of mean piston speed until about 7,950 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. A rod ratio of 2.01 is long by production standards — less side-load on the cylinder wall and gentler piston acceleration around TDC, the geometry that tolerates high RPM. Each of the 8 cylinders displaces 37.6 ci (617 cc).
8.2:1 on iron heads is low by modern standards and generally happy on regular pump fuel.
It is one of 8 engines in the Pontiac 301ci family, all of them 301 ci — the differences between them are in compression, heads and rating, not displacement.
| Displacement | 301 ci / 4.9 L |
|---|---|
| Bore | 4.002" |
| Stroke | 3.01" |
| Cylinders | 8 |
| Configuration | V8 |
| Compression ratio | 8.2:1 * |
| Rod length | 6.05" |
| Rod ratio | 2.01 |
| Bore/stroke ratio | 1.33 |
* Compression ratio from a single source; not yet cross-verified.
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Firing order | 1-8-4-3-6-5-7-2 |
| Years | 1978 |
| Bore/stroke character | 1.330 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,010 ft/min — conservative for a street engine |
| Rod ratio | 2.01 — long — less side loading on the cylinder wall, favours high RPM |
| Displacement per cylinder | 37.6 ci |
| Static compression | 8.2:1 — low by modern standards, generally happy on regular pump fuel |
Each link opens the calculator with this engine's specs already filled in.
1 factory vehicle, 1978. Each year opens that model's engine table.