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Pontiac LQ5 specs: 121 ci (2.0L) 4-cylinder, 3.50 x 3.15 in (88.9 x 80 mm) bore and stroke, 9:1 compression. Built 1985–1986. Used in the Chevrolet Cavalier.
The Pontiac 121ci (LQ5) is oversquare — the 3.5" bore exceeds the 3.15" stroke by 11.1% — a layout that favors airflow and RPM over leverage at the crank. The 3.15" stroke does not reach 4,000 ft/min of mean piston speed until about 7,600 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 4 cylinders displaces 30.3 ci (496 cc).
9:1 is low by modern standards and generally happy on regular pump fuel.
It is one of 4 engines in the Pontiac 121ci family, all of them 121 ci — the differences between them are in compression, heads and rating, not displacement. 2 factory variants share these dimensions across 1985–1986.
| Displacement | 121 ci / 2 L |
|---|---|
| Bore | 3.5" |
| Stroke | 3.15" |
| Cylinders | 4 |
| Configuration | I4 |
| Compression ratio | 9:1 |
| Bore/stroke ratio | 1.111 |
| Fuel type | gas |
|---|---|
| Years | 1985–1986 |
| Bore/stroke character | 1.111 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,150 ft/min — conservative for a street engine |
| Displacement per cylinder | 30.3 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 |
|---|---|---|
| 1985 | — | LQ5 |
| 1986 | — | LQ5 |
2 factory vehicles, 1983–1986. Each year opens that model's engine table.