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Plymouth LG specs: 225 ci (3.7L) 6-cylinder, 3.402 x 4.13 in (86.4 x 104.9 mm) bore and stroke, 8.4:1 compression. Rated 145 hp. Rod ratio and piston speed.
The Plymouth Slant-6 (LG) is undersquare — the 4.1299" stroke exceeds the 3.4016" bore by 17.6% — a layout that trades peak RPM for leverage and torque low in the range. The 4.1299" stroke puts mean piston speed at 4,000 ft/min around 5,800 RPM, which is where a production bottom end is generally considered at its limit. Each of the 6 cylinders displaces 37.5 ci (615 cc).
8.4:1 on iron heads is low by modern standards and generally happy on regular pump fuel.
It is one of 13 engines in the Slant-6 family, the largest at 225 ci. Factory fitments include the Plymouth Valiant, Plymouth Duster, Plymouth Volaré.
| Displacement | 225 ci / 3.7 L |
|---|---|
| Bore | 3.4016" |
| Stroke | 4.1299" |
| Cylinders | 6 |
| Compression ratio | 8.4:1 |
| Bore/stroke ratio | 0.824 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 145 hp |
| Bore/stroke character | 0.824 — undersquare — stroke exceeds bore, which favours low-end torque |
|---|---|
| Mean piston speed at 6,000 RPM | 4,130 ft/min — in the range typical of performance street engines |
| Displacement per cylinder | 37.5 ci |
| Static compression | 8.4:1 — low by modern standards, generally happy on regular pump fuel |
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