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Pontiac L66 specs: 455 ci (7.5L) 8-cylinder, 4.153 x 4.214 in (105.5 x 107 mm) bore and stroke, 8.2:1 compression. Rated 185-280 hp, 1971–1972.
The Pontiac 455ci (L66) is close to square: 4.153" bore against 4.214" stroke, within 1.4%, which splits the difference between a high-revving layout and a torque layout. The 4.214" stroke puts mean piston speed at 4,000 ft/min around 5,700 RPM, which is where a production bottom end is generally considered at its limit. A rod ratio of 1.572 is in the range most production engines fall in. Each of the 8 cylinders displaces 56.9 ci (932 cc).
8.2:1 on iron heads is low by modern standards and generally happy on regular pump fuel.
It is one of 6 engines in the Pontiac 455ci family, all of them 455 ci — the differences between them are in compression, heads and rating, not displacement. 3 factory variants share these dimensions, rated from 185 to 280 hp across 1971–1972.
| Displacement | 455 ci / 7.5 L |
|---|---|
| Bore | 4.153" |
| Stroke | 4.214" |
| Cylinders | 8 |
| Configuration | V8 |
| Compression ratio | 8.2:1 * |
| Rod length | 6.625" |
| Rod ratio | 1.572 |
| Bore/stroke ratio | 0.986 |
* 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 |
| Advertised HP | 185–280 hp |
| Years | 1971–1972 |
| Bore/stroke character | 0.986 — square — bore and stroke are within 5%, a balanced compromise |
|---|---|
| Mean piston speed at 6,000 RPM | 4,214 ft/min — in the range typical of performance street engines |
| Rod ratio | 1.572 — moderate — the range most production V8s fall in |
| Displacement per cylinder | 56.9 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.
These records share identical bore, stroke, displacement and compression. They differ by model year and factory power rating.
| Year | Advertised HP | Code |
|---|---|---|
| 1971 | 280 hp | L66 |
| 1972 | 185 hp | L66 |
| 1972 | 200 hp | L66 |
2 factory vehicles, 1971–1972. Each year opens that model's engine table.