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Oldsmobile L78 specs: 455 ci (7.5L) 8-cylinder, 4.126 x 4.25 in (104.8 x 108 mm) bore and stroke, 8.5:1 compression. Rated 215-250 hp, 1972–1975.
The Oldsmobile 455ci (L78) is close to square: 4.126" bore against 4.25" stroke, within 2.9%, which splits the difference between a high-revving layout and a torque layout. The 4.25" stroke puts mean piston speed at 4,000 ft/min around 5,650 RPM, which is where a production bottom end is generally considered at its limit. A rod ratio of 1.585 is in the range most production engines fall in. Each of the 8 cylinders displaces 56.9 ci (932 cc).
8.5:1 on iron heads is low by modern standards and generally happy on regular pump fuel.
It is one of 15 engines in the Oldsmobile 455ci family, all of them 455 ci — the differences between them are in compression, heads and rating, not displacement. 4 factory variants share these dimensions, rated from 215 to 250 hp across 1972–1975.
| Displacement | 455 ci / 7.5 L |
|---|---|
| Bore | 4.126" |
| Stroke | 4.25" |
| Cylinders | 8 |
| Configuration | V8 |
| Compression ratio | 8.5:1 |
| Rod length | 6.735" |
| Rod ratio | 1.585 |
| Bore/stroke ratio | 0.971 |
| 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 | 215–250 hp |
| Years | 1972–1975 |
| Year | Version | HP @ rpm | Torque @ rpm | Comp. | Duration int / exh | Valve lift int / exh | LSA |
|---|---|---|---|---|---|---|---|
| 1972 | L75 net | 250 @ 4200 | 370 lb-ft @ 2800 | 8.5:1 | 285° / 287° | 0.472" | 110° |
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 | 0.971 — square — bore and stroke are within 5%, a balanced compromise |
|---|---|
| Mean piston speed at 6,000 RPM | 4,250 ft/min — in the range typical of performance street engines |
| Rod ratio | 1.585 — moderate — the range most production V8s fall in |
| Displacement per cylinder | 56.9 ci |
| Static compression | 8.5:1 — 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 |
|---|---|---|
| 1972 | 250 hp | L78 |
| 1973 | — | L78 |
| 1974 | 230 hp | L78 |
| 1975 | 215 hp | L78 |
2 factory vehicles, 1972–1976. Each year opens that model's engine table.