Classic/Antique Car Repair: 51 dodge flathead six, compression pressure, peak pressure

Question
do you have any idea what or were to find out what the compression test psi. should be on the 218 ci inline six out of a 51' dodge pick-up?

Answer
The reason you don't find this number in any manual is that it depends on too many unknown factors.  You'll get a different reading depending on your altitude, the cranking speed, whether or not you have the carburetor throttle valve blocked open etc.

The more important measurement is how even the cylinders are. If they are all within a 10% band, and the compression pressure is around 100 PSI or better, the engine is in very good condition.

To make a rough guess at what it should be, at sea level, you can take the atmospheric pressure as 14.7 PSI.  Since the compression ratio is about 7 to 1, the peak pressure in the cylinder should be about 100 PSI- but if you are at higher altitude, it will be less (less air to compress!).

Dick