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GMC 230 specs: 230 ci (3.8L) 6-cylinder, 3.875 x 3.25 in (98.4 x 82.6 mm) bore and stroke, 8.5:1 compression. Rated 140 hp. OHV. Rod ratio and piston speed.
The GMC Chevy Straight-6 (194/230/250/292) (230) is oversquare — the 3.875" bore exceeds the 3.25" stroke by 19.2% — a layout that favors airflow and RPM over leverage at the crank. The 3.25" stroke does not reach 4,000 ft/min of mean piston speed until about 7,400 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 6 cylinders displaces 38.3 ci (628 cc).
8.5:1 on iron heads is low by modern standards and generally happy on regular pump fuel.
It is one of 10 engines in the Chevy Straight-6 (194/230/250/292) family, sitting between the 194 ci and 292 ci members. Factory fitments include the Chevrolet Chevelle, Chevrolet Camaro, Chevrolet Nova and 1 other.
| Displacement | 230 ci / 3.8 L |
|---|---|
| Bore | 3.875" |
| Stroke | 3.25" |
| Cylinders | 6 |
| Compression ratio | 8.5:1 |
| Bore/stroke ratio | 1.192 |
| Piston deck clearance | 0.011" |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 140 hp |
| Bore/stroke character | 1.192 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,250 ft/min — conservative for a street engine |
| Displacement per cylinder | 38.3 ci |
| Static compression | 8.5:1 — low by modern standards, generally happy on regular pump fuel |
| Intake valve diameter | 1.725" |
|---|---|
| Exhaust valve diameter | 1.505" |
| Chamber volume | 69.6 cc |
| Rocker ratio | 1.75:1 |
| Lifter type | hydraulic |
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