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Pontiac 191ci specs: 191 ci (3.1L) 6-cylinder, 3.50 x 3.31 in (88.9 x 84.1 mm) bore and stroke, 9:1 compression. Rated 120-140 hp, 1991–1992.
The Pontiac 191ci is oversquare — the 3.5" bore exceeds the 3.31" stroke by 5.7% — a layout that favors airflow and RPM over leverage at the crank. The 3.31" stroke does not reach 4,000 ft/min of mean piston speed until about 7,250 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 6 cylinders displaces 31.8 ci (522 cc).
9:1 on iron heads is low by modern standards and generally happy on regular pump fuel.
It is one of 6 engines in the Pontiac 191ci family, all of them 191 ci — the differences between them are in compression, heads and rating, not displacement. 3 factory variants share these dimensions, rated from 120 to 140 hp across 1991–1992.
| Displacement | 191 ci / 3.1 L |
|---|---|
| Bore | 3.5" |
| Stroke | 3.31" |
| Cylinders | 6 |
| Configuration | I6 |
| Compression ratio | 9:1 |
| Bore/stroke ratio | 1.057 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 120–140 hp |
| Years | 1991–1992 |
| Bore/stroke character | 1.057 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,310 ft/min — conservative for a street engine |
| Displacement per cylinder | 31.8 ci |
| Static compression | 9:1 — low by modern standards, generally happy on regular pump fuel |
| Intake valve diameter | 1.717" |
|---|---|
| Exhaust valve diameter | 1.425" |
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 |
|---|---|---|
| 1991 | 140 hp | — |
| 1992 | 120 hp | — |
| 1992 | 140 hp | — |