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Pontiac LT3 specs: 121 ci (2.0L) 4-cylinder, 3.386 x 3.386 in (86 x 86 mm) bore and stroke, 8:1 compression. Rated 165 hp, 1987–1990.
The Pontiac 121ci (LT3) is exactly square — 3.3858" bore and 3.3858" stroke are the same — which splits the difference between a high-revving layout and a torque layout. The 3.3858" stroke does not reach 4,000 ft/min of mean piston speed until about 7,100 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).
8:1 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. 4 factory variants share these dimensions, rated at 165 hp across 1987–1990.
| Displacement | 121 ci / 2 L |
|---|---|
| Bore | 3.3858" |
| Stroke | 3.3858" |
| Cylinders | 4 |
| Configuration | I4 |
| Compression ratio | 8:1 |
| Bore/stroke ratio | 1 |
| Fuel type | gas |
|---|---|
| Advertised HP | 165 hp |
| Years | 1987–1990 |
| Year | Version | HP @ rpm | Torque @ rpm | Comp. |
|---|---|---|---|---|
| 1987 | LT3 net | 165 @ 5600 | 175 lb-ft @ 4000 | 8:1 |
Factory specification sheet.
| Bore/stroke character | 1.000 — square — bore and stroke are within 5%, a balanced compromise |
|---|---|
| Mean piston speed at 6,000 RPM | 3,386 ft/min — conservative for a street engine |
| Displacement per cylinder | 30.3 ci |
| Static compression | 8:1 — 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 |
|---|---|---|
| 1987 | 165 hp | LT3 |
| 1988 | 165 hp | LT3 |
| 1989 | 165 hp | LT3 |
| 1990 | 165 hp | LT3 |
2 factory vehicles, 1987–1990. Each year opens that model's engine table.