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Pontiac 173ci (1989) · 130 hp specs: 173 ci (2.8L) 6-cylinder, 3.50 x 3.00 in (88.9 x 76.2 mm) bore and stroke, 9.1:1 compression. Rated 130 hp, 1989.
The Pontiac 173ci (1989) · 130 hp is oversquare — the 3.5" bore exceeds the 3" stroke by 16.7% — a layout that favors airflow and RPM over leverage at the crank. The 3" stroke does not reach 4,000 ft/min of mean piston speed until about 8,000 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. A rod ratio of 1.9 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 6 cylinders displaces 28.8 ci (472 cc).
9.1:1 on iron heads is low by modern standards and generally happy on regular pump fuel.
It is one of 8 engines in the Pontiac 173ci family, all of them 173 ci — the differences between them are in compression, heads and rating, not displacement.
| Displacement | 173 ci / 2.8 L |
|---|---|
| Bore | 3.5" |
| Stroke | 3" |
| Cylinders | 6 |
| Configuration | I6 |
| Compression ratio | 9.1:1 |
| Rod length | 5.7" |
| Rod ratio | 1.9 |
| Bore/stroke ratio | 1.167 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 130 hp |
| Years | 1989 |
| Bore/stroke character | 1.167 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,000 ft/min — conservative for a street engine |
| Rod ratio | 1.9 — long — less side loading on the cylinder wall, favours high RPM |
| Displacement per cylinder | 28.8 ci |
| Static compression | 9.1:1 — low by modern standards, generally happy on regular pump fuel |
| Intake valve diameter | 1.71" |
|---|---|
| Exhaust valve diameter | 1.42" |
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