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Chevrolet LH7 specs: 173 ci (2.8L) 6-cylinder, 3.50 x 3.00 in (88.9 x 76.2 mm) bore and stroke, 8.9:1 compression. Rated 135 hp, 1981.
The Chevrolet 173ci (LH7) 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).
8.9:1 on iron heads is low by modern standards and generally happy on regular pump fuel.
It is one of 11 engines in the Chevrolet 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 | V6 |
| Compression ratio | 8.9:1 |
| 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 | 135 hp |
| Years | 1981 |
| Year | Version | HP @ rpm | Torque @ rpm | Comp. | Duration int / exh | Valve lift int / exh | LSA |
|---|---|---|---|---|---|---|---|
| 1981 | LH7 net | 135 @ 5400 | 145 lb-ft @ 2400 | 8.9:1 | 304° / 324° | 0.393" / 0.410" | 111° |
Factory specification sheet. Durations are the factory's advertised figures at the basis printed on the sheet, not duration at .050" lift; lobe separation is calculated from the printed valve timing.
| 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 | 8.9:1 — low by modern standards, generally happy on regular pump fuel |
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5 factory vehicles, 1981–1984. Each year opens that model's engine table.