Pontiac 400ci specs: 4.125 x 3.75 in (104.8 x 95.3 mm) bore and stroke, shared by all 18 versions. Displacement, compression and factory ratings.
| Displacement | 400 ci |
|---|---|
| Cylinders | 8 |
| Bore | 4.125" |
| Stroke | 3.750" |
| Compression | 8.4–10.8:1 |
| Advertised power | 170–370 hp |
| Years | 1967–1979 |
| Cylinder head data | 3 of 18 engines |
| Engine | Displacement | Bore × Stroke | CR | HP |
|---|---|---|---|---|
| Pontiac 400ci · 4.125" × 3.750" · 8.601:1 | 400 ci | 4.125" × 3.75" | 8.601:1 | 255–265 |
| Pontiac 400ci · 4.125" × 3.750" · 10.501:1 | 400 ci | 4.125" × 3.75" | 10.501:1 | 290–350 |
| Pontiac 400ci · 4.125" × 3.750" · 10.751:1 | 400 ci | 4.125" × 3.75" | 10.751:1 | 335–360 |
| Pontiac 400ci · 4.125" × 3.750" · 8.351:1 | 400 ci | 4.125" × 3.75" | 8.351:1 | 170–185 |
| Pontiac 400ci (1977) · 180 hp | 400 ci | 4.125" × 3.75" | 8.561:1 | 180 |
| Pontiac 400ci (1977) · 200 hp | 400 ci | 4.125" × 3.75" | 9.081:1 | 200 |
| 400 4-bbl | 400 ci | 4.125" × 3.75" | — | 325–330 |
| 400 H.O. and 400 Ram Air | 400 ci | 4.125" × 3.75" | — | 335 |
| 400 Ram Air II | 400 ci | 4.125" × 3.75" | — | 340 |
| 400 H.O. | 400 ci | 4.125" × 3.75" | — | 335 |
| 400 Ram Air IV | 400 ci | 4.125" × 3.75" | — | 345 |
| L65 | 400 ci | 4.125" × 3.75" | — | 170–265 |
| L78 | 400 ci | 4.125" × 3.75" | — | 180–330 |
| L74 | 400 ci | 4.125" × 3.75" | — | 345 |
| LS1 | 400 ci | 4.125" × 3.75" | — | 345 |
| W72 | 400 ci | 4.125" × 3.75" | — | 220 |
| Pontiac 400ci (1968–1974) | 400 ci | 4.125" × 3.75" | — | 225–370 |
| XX | 400 ci | 4.125" × 3.75" | — | 265 |
Compression spans 8.351:1 to 10.751:1, so fuel requirements differ meaningfully between members — worth checking before assuming parts interchange.
All are oversquare — bore larger than stroke, which favours revs over low-end torque.
Each engine page carries rod ratio, mean piston speed, bore/stroke character and cylinder head specs where published, and links into the calculators with its dimensions already filled in.