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Pontiac 326ci (1967) · 250 hp specs: 326 ci (5.3L) 8-cylinder, 3.719 x 3.75 in (94.5 x 95.3 mm) bore and stroke, 9.201:1 compression. Rated 250 hp, 1967.
The Pontiac 326ci (1967) · 250 hp is close to square: 3.719" bore against 3.75" stroke, within 0.8%, which splits the difference between a high-revving layout and a torque layout. The 3.75" stroke puts mean piston speed at 4,000 ft/min around 6,400 RPM, which is where a production bottom end is generally considered at its limit. A rod ratio of 1.767 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 40.8 ci (668 cc).
9.201:1 on iron heads is low by modern standards and generally happy on regular pump fuel.
It is one of 6 engines in the Pontiac 326ci family, all of them 326 ci — the differences between them are in compression, heads and rating, not displacement.
| Displacement | 326 ci / 5.3 L |
|---|---|
| Bore | 3.719" |
| Stroke | 3.75" |
| Cylinders | 8 |
| Configuration | V8 |
| Compression ratio | 9.201:1 |
| Rod length | 6.625" |
| Rod ratio | 1.767 |
| Bore/stroke ratio | 0.992 |
| Piston deck clearance | 0" |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 250 hp |
| Years | 1967 |
| Bore/stroke character | 0.992 — square — bore and stroke are within 5%, a balanced compromise |
|---|---|
| Mean piston speed at 6,000 RPM | 3,750 ft/min — in the range typical of performance street engines |
| Rod ratio | 1.767 — long — less side loading on the cylinder wall, favours high RPM |
| Displacement per cylinder | 40.8 ci |
| Static compression | 9.201:1 — low by modern standards, generally happy on regular pump fuel |
| Intake valve diameter | 1.884" |
|---|---|
| Exhaust valve diameter | 1.603" |
| Chamber volume | 55 cc |
| Rocker ratio | 1.5:1 |
| Lifter type | hydraulic |
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