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Pontiac 138ci (1988) · 150 hp specs: 138 ci (2.3L) 4-cylinder, 3.625 x 3.35 in (92.1 x 85.1 mm) bore and stroke, 10.45:1 compression. Rated 150 hp, 1988. OHC.
The Pontiac 138ci (1988) · 150 hp is oversquare — the 3.625" bore exceeds the 3.35" stroke by 8.2% — a layout that favors airflow and RPM over leverage at the crank. The 3.35" stroke does not reach 4,000 ft/min of mean piston speed until about 7,150 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. A rod ratio of 1.734 is in the range most production engines fall in. Each of the 4 cylinders displaces 34.5 ci (565 cc).
10.45:1 on iron heads is in the range that usually runs on pump premium; iron holds heat, so treat it as the less forgiving side of that range.
It is one of 5 engines in the Pontiac 138ci family, all of them 138 ci — the differences between them are in compression, heads and rating, not displacement.
| Displacement | 138 ci / 2.3 L |
|---|---|
| Bore | 3.625" |
| Stroke | 3.35" |
| Cylinders | 4 |
| Configuration | I4 |
| Compression ratio | 10.45:1 |
| Rod length | 5.81" |
| Rod ratio | 1.734 |
| Bore/stroke ratio | 1.082 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHC |
| Fuel type | gas |
| Advertised HP | 150 hp |
| Years | 1988 |
| Bore/stroke character | 1.082 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,350 ft/min — conservative for a street engine |
| Rod ratio | 1.734 — moderate — the range most production V8s fall in |
| Displacement per cylinder | 34.5 ci |
| Static compression | 10.45:1 — in the range that usually runs on pump premium |
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