What is a good compression pressure for a 4.7:1 CR?

Turbo Dog

New User
I am looking forward to picking up what should be a good running 1936 B this Sunday. I have done compression tests on automotive engines but their normal compression ratios are twice what this engine has. What is a normal good compression pressure for a 1936 B?
 
I think I figured it out.

If I was at sea level, 14.7 psi atmospheric pressure, and I multiply that times the compression ration I get the compression pressure at sea level.

For example, testing automotive engines with 8.5:1 compression ratio I would normally see 125 psi. So I now live at 7400 ft and atmospheric pressure is about 11.4 so the engine compression pressure should be 11.4 x 4.7 = 54 psi.
 
I should add that since it is a normally aspirated engine the pressure of the air coming into the cylinder will be slightly below the local atmospheric pressure. So it won't hit the ideal theoretical compression pressure of 54 psi, might be something around 50 psi.
 
I was thinking the all fuel engine specs. are to be around 75 psi at Ohio sea level. Your results may vary.
 
Assuming 14.7 PSI at sea level is fine. There are some
losses, so it will be slightly lower than the calculated figure.
But it is a good guide.
 
Field Service Bulletin 167-S (Feb 15, 1950) says the compression ratio of a ?36 B (S/N 12012 ? 27388) is actually 3.90:1. A compression ratio of 4.71:1 didn?t occur until the beginning of the 1941 model year (S/N 96000). That bulletin states the compression pressure should be 60 PSI for the 3.9 ratio and 70 PSI for the 4.71 ratio.
 

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