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Pontiac 370ci (1958) specs: 370 ci (6.1L) 8-cylinder, 4.063 x 3.563 in (103.2 x 90.5 mm) bore and stroke. Rated 255-310 hp, 1958.
The Pontiac 370ci (1958) is oversquare — the 4.063" bore exceeds the 3.563" stroke by 14.0% — a layout that favors airflow and RPM over leverage at the crank. The 3.563" stroke puts mean piston speed at 4,000 ft/min around 6,750 RPM, which is where a production bottom end is generally considered at its limit. A rod ratio of 1.859 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 46.3 ci (758 cc).
It is one of 2 engines in the Pontiac 370ci family, all of them 370 ci — the differences between them are in compression, heads and rating, not displacement. 4 factory variants share these dimensions, rated from 255 to 310 hp in 1958.
| Displacement | 370 ci / 6.1 L |
|---|---|
| Bore | 4.063" |
| Stroke | 3.563" |
| Cylinders | 8 |
| Configuration | V8 |
| Compression ratio | 8.6–10.5:1 (published figures vary) |
| Rod length | 6.625" |
| Rod ratio | 1.859 |
| Bore/stroke ratio | 1.14 |
| Fuel type | gas |
|---|---|
| Firing order | 1-8-4-3-6-5-7-2 |
| Advertised HP | 255–310 hp |
| Years | 1958 |
| Year | Version | HP @ rpm | Torque @ rpm | Comp. |
|---|---|---|---|---|
| 1958 | gross | 255 @ 4500 | 360 lb-ft @ 2600 | 8.6:1 |
| 1958 | gross | 285 @ 4600 | 395 lb-ft @ 2800 | 10:1 |
| 1958 | gross | 300 @ 4600 | 400 lb-ft @ 3000 | 10.5:1 |
| 1958 | gross | 310 @ 4800 | 400 lb-ft @ 3400 | 10.5:1 |
Factory specification sheet.
| Bore/stroke character | 1.140 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,563 ft/min — in the range typical of performance street engines |
| Rod ratio | 1.859 — long — less side loading on the cylinder wall, favours high RPM |
| Displacement per cylinder | 46.3 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 |
|---|---|---|
| 1958 | 255 hp | — |
| 1958 | 285 hp | — |
| 1958 | 300 hp | — |
| 1958 | 310 hp | — |
1 factory vehicle, 1958. Each year opens that model's engine table.