How hard is it to perform compression test and how do you do it??????

I have a 71 350, thx

 

It's easy.

Remove all the spark plugs, unplug the 12V to the distributor, unplug the injectors or fuse or whatever is easiest to make sure you don't fill the motor with gas, block the throttle wide open, screw the adapter into a plug hole, hook the gauge to it, spin the motor about 5 or 6 full revolutions, read the gauge, reset the gauge, repeat for next cylinder.

 

this is mainly used to check for bad rings or valves right?? And how are you suppose to know how much it should measure, or do you just compare all the cylinders together to see if they are measuring about the same?

 

You are mainly looking for consistency among the all the cylinders, like +-10%. I don't think there's any specific reading that'll tell if your motor is in good condition. I think a motor in decent condition will pull 150 psi or more. If a cylinder has a very low reading, squirt some oil in that cylinder and see if the reading goes up a lot. If it does, you have worn rings. If it doesn't, you might have a leaky headgasket or a valve that isn't seating properly.