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Pontiac LR8 specs: 151 ci (2.5L) 4-cylinder, 4.00 x 3.00 in (101.6 x 76.2 mm) bore and stroke, 8.2:1 compression. Rated 90 hp. Rod ratio and piston speed.
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).
8.2:1 on iron heads is low by modern standards and generally happy on regular pump fuel.
It is one of 2 engines in the Iron Duke family, all of them 151 ci — the differences between them are in compression, heads and rating, not displacement. 2 factory variants share these dimensions, rated at 90 hp. Factory fitments include the Pontiac Phoenix, Pontiac Fiero, Pontiac Grand Am and 4 others.
| Displacement | 151 ci / 2.5 L |
|---|---|
| Bore | 4" |
| Stroke | 3" |
| Cylinders | 4 |
| Compression ratio | 8.2:1 |
| Bore/stroke ratio | 1.333 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 90 hp |
| 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 | 8.2:1 — 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 |
|---|---|---|
| — | 90 hp | LR8 |
| — | 90 hp | LR8, 2.5L I4, LX8, LX9 |