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Ford 250ci (1970) specs: 250 ci (4.1L) 6-cylinder, 3.682 x 3.91 in (93.5 x 99.3 mm) bore and stroke. Rated 155 hp, 1970. OHV. Rod ratio and piston speed.
The Ford 250ci (1970) is undersquare — the 3.91" stroke exceeds the 3.682" bore by 5.8% — a layout that trades peak RPM for leverage and torque low in the range. The 3.91" stroke puts mean piston speed at 4,000 ft/min around 6,150 RPM, which is where a production bottom end is generally considered at its limit. A rod ratio of 1.504 is short — higher piston acceleration and more side-load, typical of stroker combinations and a reason to watch piston speed closely. Each of the 6 cylinders displaces 41.7 ci (683 cc).
It is one of 6 engines in the Ford 250ci family, all of them 250 ci — the differences between them are in compression, heads and rating, not displacement.
| Displacement | 250 ci / 4.1 L |
|---|---|
| Bore | 3.682" |
| Stroke | 3.91" |
| Cylinders | 6 |
| Configuration | I6 |
| Rod length | 5.88" |
| Rod ratio | 1.504 |
| Bore/stroke ratio | 0.942 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 155 hp |
| Years | 1970 |
| Bore/stroke character | 0.942 — undersquare — stroke exceeds bore, which favours low-end torque |
|---|---|
| Mean piston speed at 6,000 RPM | 3,910 ft/min — in the range typical of performance street engines |
| Rod ratio | 1.504 — short — more side loading and piston dwell at TDC, typical of stroker combinations |
| Displacement per cylinder | 41.7 ci |
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