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Chevrolet LD4 specs: 250 ci (4.1L) 6-cylinder, 3.875 x 3.53 in (98.4 x 89.7 mm) bore and stroke. Rated 100 hp, 1976–1978. Used in the Chevrolet K5 Blazer.
The Chevrolet 250ci (LD4) is oversquare — the 3.875" bore exceeds the 3.53" stroke by 9.8% — a layout that favors airflow and RPM over leverage at the crank. The 3.53" stroke puts mean piston speed at 4,000 ft/min around 6,800 RPM, which is where a production bottom end is generally considered at its limit. A rod ratio of 1.615 is in the range most production engines fall in. Each of the 6 cylinders displaces 41.7 ci (683 cc).
It is one of 6 engines in the Chevrolet 250ci family, all of them 250 ci — the differences between them are in compression, heads and rating, not displacement. 3 factory variants share these dimensions, rated at 100 hp across 1976–1978.
| Displacement | 250 ci / 4.1 L |
|---|---|
| Bore | 3.875" |
| Stroke | 3.53" |
| Cylinders | 6 |
| Configuration | I6 |
| Rod length | 5.7" |
| Rod ratio | 1.615 |
| Bore/stroke ratio | 1.098 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 100 hp |
| Years | 1976–1978 |
| Bore/stroke character | 1.098 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,530 ft/min — in the range typical of performance street engines |
| Rod ratio | 1.615 — moderate — the range most production V8s fall in |
| Displacement per cylinder | 41.7 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 |
|---|---|---|
| 1976 | 100 hp | LD4 |
| 1977 | 100 hp | LD4 |
| 1978 | 100 hp | LD4 |