See other engines in this family
Pontiac LR8 specs: 151 ci (2.5L) 4-cylinder, 4.00 x 3.00 in (101.6 x 76.2 mm) bore and stroke, 9:1 compression. Rated 90-110 hp, 1982–1990.
The Pontiac Iron Duke (LR8) is oversquare — the 4" bore exceeds the 3" stroke by 33.3% — 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. Each of the 4 cylinders displaces 37.8 ci (619 cc).
9:1 on iron heads is low by modern standards and generally happy on regular pump fuel.
It is one of 3 engines in the Iron Duke family, all of them 151 ci — the differences between them are in compression, heads and rating, not displacement. 12 factory variants share these dimensions, rated from 90 to 110 hp across 1982–1990.
| Displacement | 151 ci / 2.5 L |
|---|---|
| Bore | 4" |
| Stroke | 3" |
| Cylinders | 4 |
| Configuration | I4 |
| Compression ratio | 9:1 |
| Bore/stroke ratio | 1.333 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 90–110 hp |
| Years | 1982–1990 |
| Year | Version | HP @ rpm | Torque @ rpm | Comp. |
|---|---|---|---|---|
| 1984 | LR8/LQ9 net | 92 @ 4400 | 132 lb-ft @ 2800 | 9:1 |
| 1987 | L68 net | 98 @ 4800 | 135 lb-ft @ 3200 | 9:1 |
Factory specification sheet.
| Bore/stroke character | 1.333 — 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 |
| Displacement per cylinder | 37.8 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 |
|---|---|---|
| 1982 | — | LR8 |
| 1983 | — | LR8 |
| 1983 | 90 hp | LR8 |
| 1984 | — | LR8 |
| 1984 | 92 hp | LR8 |
| 1985 | — | LR8 |
| 1986 | — | LR8 |
| 1987 | 98 hp | LR8 |
| 1988 | 98 hp | LR8 |
| 1989 | — | LR8 |
| 1989 | 110 hp | LR8 |
| 1990 | 110 hp | LR8 |
10 factory vehicles, 1982–1992. Each year opens that model's engine table.