I'm in on the valve idea, what would timing have to do with it? Check your rocker arm adjustment and make sure they are correct. Is it a hydraulic cam? If it is, you could have a lifter that is siezed/jammed solid. This will cause the popping in the exhaust, as your exhaust valve on the effected cylinder/s will never close. This does not however explain the fact that you are reading 175psi consistant on all cylinders unless you have lifters that are pumping up solid when
oil pressure is applied which would not be present when just cranking an engine over. If it is a solid lifter cam, they are adjusted differently than a hydraulic cam.
Let us know your progress.
John