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Chevrolet 409ci specs: 409 ci (6.7L) 8-cylinder, 4.313 x 3.50 in (109.6 x 88.9 mm) bore and stroke, 11:1 compression. Rated 400 hp, 1965.
The Chevrolet 409ci is oversquare — the 4.313" bore exceeds the 3.5" stroke by 23.2% — a layout that favors airflow and RPM over leverage at the crank. The 3.5" stroke puts mean piston speed at 4,000 ft/min around 6,850 RPM, which is where a production bottom end is generally considered at its limit. A rod ratio of 1.717 is in the range most production engines fall in. Each of the 8 cylinders displaces 51.1 ci (838 cc).
11:1 is high enough that pump premium or better is normally required.
It is one of 7 engines in the Chevrolet 409ci family, all of them 409 ci — the differences between them are in compression, heads and rating, not displacement.
| Displacement | 409 ci / 6.7 L |
|---|---|
| Bore | 4.313" |
| Stroke | 3.5" |
| Cylinders | 8 |
| Compression ratio | 11:1 |
| Rod length | 6.01" |
| Rod ratio | 1.717 |
| Bore/stroke ratio | 1.232 |
| Piston deck clearance | 0.011" |
| Induction | 1-4 |
|---|---|
| Advertised HP | 400 hp |
| Years | 1965 |
| Bore/stroke character | 1.232 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,500 ft/min — conservative for a street engine |
| Rod ratio | 1.717 — moderate — the range most production V8s fall in |
| Displacement per cylinder | 51.1 ci |
| Static compression | 11:1 — high enough that pump premium or better is normally required |
| Intake valve diameter | 2.195" |
|---|---|
| Exhaust valve diameter | 1.725" |
| Rocker ratio | 1.75:1 |
| Lifter type | mechanical |
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