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Pontiac 260ci (1976) specs: 260 ci (4.3L) 8-cylinder, 3.50 x 3.385 in (88.9 x 86 mm) bore and stroke. Rated 110 hp, 1976. Used in the Pontiac LeMans. OHV.
The Pontiac 260ci (1976) is close to square: 3.5" bore against 3.385" stroke, within 3.4%, which splits the difference between a high-revving layout and a torque layout. The 3.385" stroke does not reach 4,000 ft/min of mean piston speed until about 7,100 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. A rod ratio of 1.773 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 32.5 ci (533 cc).
It is one of 2 engines in the Pontiac 260ci family, all of them 260 ci — the differences between them are in compression, heads and rating, not displacement.
| Displacement | 260 ci / 4.3 L |
|---|---|
| Bore | 3.5" |
| Stroke | 3.385" |
| Cylinders | 8 |
| Configuration | V8 |
| Rod length | 6.002" |
| Rod ratio | 1.773 |
| Bore/stroke ratio | 1.034 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 110 hp |
| Years | 1976 |
| Bore/stroke character | 1.034 — square — bore and stroke are within 5%, a balanced compromise |
|---|---|
| Mean piston speed at 6,000 RPM | 3,385 ft/min — conservative for a street engine |
| Rod ratio | 1.773 — long — less side loading on the cylinder wall, favours high RPM |
| Displacement per cylinder | 32.5 ci |
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