390 tear down.

[tbolt]

So I recently tore down my 390 in my 63 galaxie.  Car felt underwhelming power wise and only had about 15psi of oil pressure hot when idling.  So from what I can tell I have a 360 crank in it with long rods, and a 390 piston.  I’ve had some trouble finding info on whether or not the 360 piston and 390 piston are the same.  My question is with this combination do I have 360 ci or 390 ci of displacement?  And why would someone use this combination of parts?  I’m gonna build a striker out of a different block, so really I’m just curious now about what and why I have what I have.

[BigBlueIron]

You have a 360. 360 and 390 share the same bore of 4.05 and in several applications the same piston as far as pin height is concerned. I have removed factory pistons marked 360 or 390 from the same block.
A 360 is basically a 352 with a bigger piston that is way down in the hole providing horrible compression/quench.

[tbolt]

That’s what I thought, but wasn’t sure if you could mess around with piston pin height to get the quench/compression,  it definitely ran like it had horrible compression.  Before I tore it down I did a compression check and only mustered up 120/cylinder.  It was super reliable but just had no go in it.