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Pontiac OHC-6 specs: 250 ci (4.1L) 6-cylinder, 3.874 x 3.531 in (98.4 x 89.7 mm) bore and stroke, 9:1 compression. Rated 165-175 hp. SOHC.
The Pontiac OHC-6 is oversquare — the 3.874" bore exceeds the 3.5315" stroke by 9.7% — a layout that favors airflow and RPM over leverage at the crank. The 3.5315" stroke puts mean piston speed at 4,000 ft/min around 6,800 RPM, which is where a production bottom end is generally considered at its limit. Each of the 6 cylinders displaces 41.7 ci (683 cc).
9:1 on iron heads is low by modern standards and generally happy on regular pump fuel.
It is one of 4 engines in the Pontiac OHC-6 family, the largest at 250 ci. 4 factory variants share these dimensions, rated from 165 to 175 hp. Factory fitments include the Pontiac Firebird, Pontiac LeMans, Pontiac Tempest and 3 others.
| Displacement | 250 ci / 4.1 L |
|---|---|
| Bore | 3.874" |
| Stroke | 3.5315" |
| Cylinders | 6 |
| Compression ratio | 9:1 |
| Bore/stroke ratio | 1.097 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | SOHC |
| Fuel type | gas |
| Advertised HP | 165–175 hp |
| Bore/stroke character | 1.097 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,532 ft/min — in the range typical of performance street engines |
| Displacement per cylinder | 41.7 ci |
| Static compression | 9:1 — low by modern standards, generally happy on regular pump fuel |
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 |
|---|---|---|
| — | 165 hp | OHC-6, 250 |
| — | 175 hp | 250 OHC-6 |
| — | 175 hp | OHC-6 |
| — | 175 hp | OHC-6 250, OHC-6 (250ci 1-barrel), 250 OHC, 250 OHC-6, OHC-6 |