500, 472, 425, 368 Discussion, Compression Test on 472 in Cadillac Engine Technical Discussion; So my wife inherited a '69 Coupe DeVille with a freshly rebuilt 472. She drove it for about 20,000 miles ...
So my wife inherited a '69 Coupe DeVille with a freshly rebuilt 472. She drove it for about 20,000 miles and then parked it about 7 years ago prior to us getting together. Due to time and money restraints, I haven't had a chance to really take a look at it until recently. Last week I decided to try and get it up and running and was able to do so with very little trouble. The engine has some performance upgrades (Edelbrock carb and intake, Mallory ignition, and from the sounds of things a cam) and I'd like to try to determine a few more things so I know what I'm working with. I'd also like to see if sitting for 7 years had any negative effects on the engine. So my questions are: How many psi should a stock 472 put out during a compression test and how can I determine compression ratio from the test?
Automobile(s): 1977 Coupe (blue), 1977 Coupe (yellow), 1977 Coupe (green)
Re: Compression Test on 472
When you do a compression test, your not neccessarily looking for the numbers, but the range of difference of the readings. A high compression engine will generally have about 150# readings.
Take and record your readings. If your readings are more than 15#s out of the mean average range of the readings, you should do more diagnostics to determine the reason.
Those numbers look OK for an engine that has sat idle for some years. After it gets driven for a while, the numbers may come up a bit. Adding some Marvel Mystery oil to the engine oil should help clean things up in there, like the lifters, rings, etc.