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Oldsmobile W33 specs: 455 ci (7.5L) 8-cylinder, 4.126 x 4.25 in (104.8 x 108 mm) bore and stroke, 10.25:1 compression. Rated 390 hp, 1968–1970.
The Oldsmobile 455ci (W33) 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).
10.25:1 on iron heads is in the range that usually runs on pump premium; iron holds heat, so treat it as the less forgiving side of that range.
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. 3 factory variants share these dimensions, rated at 390 hp across 1968–1970.
| Displacement | 455 ci / 7.5 L |
|---|---|
| Bore | 4.126" |
| Stroke | 4.25" |
| Cylinders | 8 |
| Configuration | V8 |
| Compression ratio | 10.25:1 |
| 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 | 390 hp |
| Years | 1968–1970 |
| Year | Version | HP @ rpm | Torque @ rpm | Comp. |
|---|---|---|---|---|
| 1969 | L32 gross | 390 @ 5000 | 500 lb-ft @ 3200 | 10.25:1 |
| 1970 | W33 gross | 390 @ 5000 | 500 lb-ft @ 3200 | 10.25:1 |
Factory specification sheet.
| 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 | 10.25:1 — in the range that usually runs on pump premium |
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 |
|---|---|---|
| 1968 | 390 hp | W33 |
| 1969 | 390 hp | W33 |
| 1970 | 390 hp | W33 |
2 factory vehicles, 1968–1970. Each year opens that model's engine table.