can you get a good read on compression while the motor is out via battery on the starter..

by doin this.. what rpm is the motor crankin at.. what numbers should be expected.. typical?

we used to set a battery charger to jump start and get accurate compression numbers.

Pressures will vary with cranking speed, typically 200 to 300 RPM, with corresponding compression pressures from around 70 to 100 psi.

the biggest difference in the numbers varies from using a rotary tester to a piston compression tester. in my own experience the piston tester will read low