Can anyone tell me what the compression should read on a 1950 216 chevy engine? The service manual says the comp ratio is a whooping 6.6:1 but doesn't say what the readings for a comp test should be. All six cyls.are read around 90. Thanks in advance.

120 would be about perfect with engine warm. You'll find the info under Tune Up Specs in your manual.

If you have 90# your in great shape.

Greetings . . .

90 PSI is a decent number for one of these old engines.

Measuring compression ratio with a PSI gauge depends on the starting the point (barometric pressure) - which is dependent on ambient temprature, engine temp, humidity and elevation with respect to sea level. At sea level with a steady barometer, one atmosphere is roughly 14.7 psi.

So if your car is sitting with a cold engine at sea level then your 90 PSI reading is about a 6:1 compression ratio - or six atmospheres. Spec would be just under 100 PSI. If, however, your car is sitting in Denver CO the starting pressure is lower so your CR would be higher with 90 PSI reading.

Here's an online pressure calculator that you can experiment with:
PSI to Atmospheres Converter

regards,
Keith

Thanks for the responses. I feel better knowing that you both agree 90 is a decent reading for that motor. Thanks again....I appreciate it!

The raw number is not as important as consistency. 90 on all six is jus' fine. 65 on one cylinder with 90 in the others, or significant variation (10 psi or more) in every cylinder, would indicate trouble.

God's Peace to you.

d
Inliner # 1450

The absolute numbers are also highly dependent on engine cranking speed. Try checking compression on 6 volts and then on 12 volts and you will see what I mean. 90 seems good to me.