Compression/Leakdown Test

[gvr4550]

i have a 1g 6bolt .020 over 2g pistons put in arp head studs and felpro head gasket 170miles and i lose compression on #4 cylinder idle lumpy drive home
No oil in water, pull plugs no sign of detenation
Do a compression test #4 0psi #3 125psi #2 120psi #1 115psi

Then crank it over to tdc and put about 60psi in #4 cylinder and air comes out of #3 cylinder spark plug hole! Same with cylinder #1 air comes out of #2.
What causes that?
Also had radiator cap off and no air bubbles

Pulled head off and head gasket looks good the compression rings arent burnt or distorted or anything.

 

[TalonTsi_291]

The only way compression would be escaping from cylinder to cylinder is the head gasket. And 120 psi on a rebuild is pretty low. So hg is where id start man.