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Chevrolet 409ci 4.125" bore specs: 409 ci (6.7L) 8-cylinder, 4.125 x 3.825 in (104.8 x 97.2 mm) bore and stroke. Rated 450 hp, 2016–2017. OHV.
The Chevrolet 409ci 4.125" bore is oversquare — the 4.125" bore exceeds the 3.825" stroke by 7.8% — a layout that favors airflow and RPM over leverage at the crank. The 3.825" stroke puts mean piston speed at 4,000 ft/min around 6,250 RPM, which is where a production bottom end is generally considered at its limit. A rod ratio of 1.621 is in the range most production engines fall in. Each of the 8 cylinders displaces 51.1 ci (838 cc).
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. 2 factory variants share these dimensions, rated at 450 hp across 2016–2017.
| Displacement | 409 ci / 6.7 L |
|---|---|
| Bore | 4.125" |
| Stroke | 3.825" |
| Cylinders | 8 |
| Configuration | V8 |
| Rod length | 6.2" |
| Rod ratio | 1.621 |
| Bore/stroke ratio | 1.078 |
| Piston deck clearance | 0.01" |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 450 hp |
| Years | 2016–2017 |
| Bore/stroke character | 1.078 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,825 ft/min — in the range typical of performance street engines |
| Rod ratio | 1.621 — moderate — the range most production V8s fall in |
| Displacement per cylinder | 51.1 ci |
| Intake valve diameter | 2.205" |
|---|---|
| Exhaust valve diameter | 1.615" |
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These records share identical bore, stroke, displacement and compression. They differ by model year and factory power rating.
| Year | Advertised HP | Code |
|---|---|---|
| 2016 | 450 hp | — |
| 2017 | 450 hp | — |