Is there any way to test compression with the head removed? Is it even possible to do it in a car that doesnt even run? It'll crank but has 0 idle!

 

You can vaccuum test the head, but no the block.

 

what would a vaccum determine.... im trying to figure out if i got a valve issue is piston issue. The only way of doin that is compression testing

 

You need to have the head on the car since the head gasket would seal the whole thing

the car dosnt need to run for a compression test, you dont even need to have the motor in the car to do it.

 

Everyone is correct, there is a running compression test and there is a relative compression test and then the usual dry compression test and the wet compression test to check rings and then the infamous leak down test that checks rings and valves (leaky or burnt) and gasket and even a hole in the piston, and a shop air injection test for the poor mans method of leak down test without a gauge.

They all require the head to be on and only the running compression test requires the engine to be actually running. Did I miss anything.