This is my first time doing this. Not sure how the RPM comes into play here.
Also, will a brand new engine have a PSI at the higher end of the scale? Im trying to figure out if my engine has ever been rebuilt and how much wear is on it (My engine is 8.6:1 C/R)
What Bluebird said. Also if you squirt oil into the cylinders after taking the initial readings it will give you an idea of how badly the rings are worn. If you see a big change, the rings are worn.
The service manual lists a 350 2 BBL at 9.2:1 and a 350 Qjet as 10.5:1 CR. The rpm factor is as the piston compresses the gases in the cylinder some leaks out past the rings and maybe past the valves, if the engine was only turned over at one rpm some would escape faster than the piston could compress them, hence the test rpm of 155-165. What ever your starter will turn the engine over with all the plugs out will be fine. I wouldn't worry a great deal if the readings are a bit on the low side as long as all eight are close to the same reading. If one or two are a good deal lower you may have a problem in those cylinders.