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Plymouth RG specs: 198 ci (3.2L) 6-cylinder, 3.402 x 3.559 in (86.4 x 90.4 mm) bore and stroke, 8.4:1 compression. Rated 125 hp. Rod ratio and piston speed.
The Plymouth Slant-6 (RG) is close to square: 3.4016" bore against 3.5591" stroke, within 4.4%, which splits the difference between a high-revving layout and a torque layout. The 3.5591" stroke puts mean piston speed at 4,000 ft/min around 6,750 RPM, which is where a production bottom end is generally considered at its limit. Each of the 6 cylinders displaces 33.0 ci (541 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, sitting between the 170 ci and 225 ci members. Factory fitments include the Plymouth Valiant, Plymouth Duster.
| Displacement | 198 ci / 3.2 L |
|---|---|
| Bore | 3.4016" |
| Stroke | 3.5591" |
| Cylinders | 6 |
| Compression ratio | 8.4:1 |
| Bore/stroke ratio | 0.956 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 125 hp |
| Bore/stroke character | 0.956 — square — bore and stroke are within 5%, a balanced compromise |
|---|---|
| Mean piston speed at 6,000 RPM | 3,559 ft/min — in the range typical of performance street engines |
| Displacement per cylinder | 33.0 ci |
| Static compression | 8.4:1 — low by modern standards, generally happy on regular pump fuel |
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