Pontiac 421ci 10.5:1 Specs
Pontiac Pontiac 421ci · 4.093" × 4" · 10.5:1 engine specs: 421 ci (6.9L), 8-cylinder, 4.093" bore x 4" stroke, 10.5:1 compression.
Dimensions
| Displacement | 421 ci / 6.9 L |
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| Bore | 4.093" |
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| Stroke | 4" |
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| Cylinders | 8 |
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| Compression ratio | 10.5:1 |
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| Rod length | 6.625" |
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| Rod ratio | 1.656 |
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| Bore/stroke ratio | 1.023 |
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| Piston deck clearance | 0" |
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Construction
| Induction | 1-4 |
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| Advertised HP | 320–338 hp |
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| Years | 1964–1966 |
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What these numbers mean
| Bore/stroke character | 1.023 — square — bore and stroke are within 5%, a balanced compromise |
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| Mean piston speed at 6,000 RPM | 4,000 ft/min — in the range typical of performance street engines |
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| Rod ratio | 1.656 — moderate — the range most production V8s fall in |
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| Displacement per cylinder | 52.6 ci |
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| Static compression | 10.5:1 — in the range that usually runs on pump premium |
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Cylinder head
| Intake valve diameter | 1.923" |
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| Exhaust valve diameter | 1.663" |
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| Chamber volume | 71.3 cc |
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| Rocker ratio | 1.5:1 |
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| Lifter type | hydraulic |
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Variants sharing these dimensions (3)
These records share identical bore, stroke, displacement and compression. They differ by model year and factory power rating.
| Year | Advertised HP | Code |
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| 1964 | 320 hp | — |
| 1965 | 338 hp | — |
| 1966 | 338 hp | — |
Similar engines
Source: NHRA blueprints — nhra.net blueprints
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