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Pontiac 400ci (1967–1974) specs: 400 ci (6.6L) 8-cylinder, 4.125 x 3.75 in (104.8 x 95.3 mm) bore and stroke. Rated 225-370 hp, 1967–1974.
The Pontiac 400ci (1967–1974) is oversquare — the 4.125" bore exceeds the 3.75" stroke by 10.0% — a layout that favors airflow and RPM over leverage at the crank. The 3.75" stroke puts mean piston speed at 4,000 ft/min around 6,400 RPM, which is where a production bottom end is generally considered at its limit. A rod ratio of 1.767 is long by production standards — less side-load on the cylinder wall and gentler piston acceleration around TDC, the geometry that tolerates high RPM. Each of the 8 cylinders displaces 50.0 ci (819 cc).
It is one of 17 engines in the Pontiac 400ci family, all of them 400 ci — the differences between them are in compression, heads and rating, not displacement. 23 factory variants share these dimensions, rated from 225 to 370 hp across 1967–1974.
| Displacement | 400 ci / 6.6 L |
|---|---|
| Bore | 4.125" |
| Stroke | 3.75" |
| Cylinders | 8 |
| Configuration | V8 |
| Compression ratio | 8.2–10.75:1 (published figures vary) |
| Rod length | 6.625" |
| Rod ratio | 1.767 |
| Bore/stroke ratio | 1.1 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Firing order | 1-8-4-3-6-5-7-2 |
| Advertised HP | 225–370 hp |
| Years | 1967–1974 |
| Year | Version | HP @ rpm | Torque @ rpm | Comp. | Duration int / exh | Valve lift int / exh | LSA |
|---|---|---|---|---|---|---|---|
| 1968 | gross | 265 @ 4600 | 397 lb-ft @ 2400 | 8.6:1 | 269° / 277° | 0.376" / 0.412" | — |
| 1968 | gross | 290 | 428 lb-ft | 10.5:1 | — | — | — |
| 1968 | gross | 340 | 445 lb-ft | 10.5:1 | — | — | — |
| 1968 | gross | 350 @ 5000 | 445 lb-ft @ 3000 | 10.75:1 | 273° / 289° | 0.410" / 0.413" | — |
| 1968 | 400 H.O. gross | 360 @ 5100 | 445 lb-ft @ 3600 | 10.75:1 | — | — | — |
| 1969 | gross | 265 @ 4600 | 355 lb-ft @ 2800 | 9.2:1 | 269° / 277° | 0.376" / 0.412" | — |
| 1969 | gross | 290 | 428 lb-ft | 10.5:1 | — | — | — |
| 1969 | gross | 366 @ 5100 | 445 lb-ft @ 3600 | 10.75:1 | — | — | — |
| 1969 | 400 Ram Air IV gross | 370 @ 5500 | 445 lb-ft @ 3900 | 10.75:1 | 308° / 320° | 0.520" | — |
| 1970 | L65 gross | 265 | 397 lb-ft | 8.8:1 | — | — | — |
| 1970 | gross | 290 | 428 lb-ft | 10:1 | — | — | — |
| 1970 | L78 gross | 330 | 445 lb-ft | 10:1 | — | — | — |
| 1970 | L78 gross | 350 @ 5000 | 445 lb-ft @ 3000 | 10.25:1 | — | — | — |
| 1970 | L74 gross | 366 @ 5100 | 445 lb-ft @ 3600 | 10.5:1 | 288° / 302° | 0.414" / 0.413" | 116° |
| 1970 | LS1 gross | 370 @ 5500 | 445 lb-ft @ 3900 | 10.5:1 | 308° / 320° | 0.527" | 113.5° |
| 1971 | L65 gross | 265 @ 4400 | 400 lb-ft @ 2400 | 8.2:1 | 269° / 277° | 0.377" / 0.411" | — |
| 1971 | L78 gross | 300 @ 4800 | 400 lb-ft @ 3600 | 8.2:1 | 273° / 289° | 0.410" / 0.413" | — |
| 1972 | L78 net | 250 @ 4400 | 325 lb-ft @ 3200 | 8.2:1 | 273° / 289° | 0.410" / 0.413" | 113.5° |
Factory specification sheet. Durations are the factory's advertised figures at the basis printed on the sheet, not duration at .050" lift; lobe separation is calculated from the printed valve timing.
| Bore/stroke character | 1.100 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,750 ft/min — in the range typical of performance street engines |
| Rod ratio | 1.767 — long — less side loading on the cylinder wall, favours high RPM |
| Displacement per cylinder | 50.0 ci |
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 |
|---|---|---|
| 1967 | 325 hp | — |
| 1968 | 265 hp | — |
| 1968 | 290 hp | — |
| 1968 | 340 hp | — |
| 1968 | 350 hp | — |
| 1968 | 360 hp | — |
| 1968 | 366 hp | — |
| 1969 | 265 hp | — |
| 1969 | 290 hp | — |
| 1969 | 340 hp | — |
| 1969 | 366 hp | — |
| 1969 | 370 hp | — |
| 1970 | 265 hp | — |
| 1970 | 290 hp | — |
| 1970 | 330 hp | — |
| 1970 | 350 hp | — |
| 1970 | 366 hp | — |
| 1970 | 370 hp | — |
| 1971 | 265 hp | — |
| 1971 | 300 hp | — |
| 1972 | 250 hp | — |
| 1973 | 230 hp | — |
| 1974 | 225 hp | — |
7 factory vehicles, 1967–1974. Each year opens that model's engine table.