Ihc never published definitive diagnostic information such as compression test limits (hot and cold), leakdown rates, etc.
The compression ratio of a 304 is just a tad higher than a 345, but lower than a 266. So baseline compression numbers would vary to a degree amongst the sv engine family.
My testing over the years tells me that an "average" condition sv motor (or I-4 for that matter) will make a "cold" compression number of a nominal 165psi. A broken-in freshly-built motor with tight valve work and fresh cylinders might give 175psi cold with a oem cam spec.
A "worn" engine (typical 80>100k miles) with no particular internal damage other than worn rings and typical valve/seat condition will show a nominal 135>145psi cold.
If a "hot" compression test is then performed, those cold numbers will bump about 10% if there are no internal problems.
Since all sv motors used the same basic camshaft spec, then cam timing variations does not enter into this picture unless ya have a cylinder(s) that are way off and a worn cam lobe(s) are suspect.
If the motor in question has been sitting non-rotated for some time, then I'd advise ya to do the "pre-oil" procedure described in this thread, post #3 before ever allowing the crankshaft to turn:
http://www.forums.IHPartsAmerica.co...I-4-sv-engine-non-oiling-rocker-assembly.html
Quick and dirty version of a compression test setup:
1) all plugs removed.
2) disable ignition electrically (disconnect coil primary, never crank over an electronic ignition system without a "load" on the coil secondary as in removing just the coil secondary cable).
3) block throttle and choke plates to wide open position.
4) fully charged battery.
5) compression gauge installed in cylinder under test tightly to prevent any compression leakage.
6) rudimentary "chart" to record compression test data results.
7) crank engine for each cylinder test until highest reading is obtained for each cylinder and record data. That should not be more than say a 10 second crankover, let the starter "cool down" between cylinder tests!
8) if battery charge levels drops so that brisk cranking cannot continue, then set up a battery charger or jump it for the duration of testing.
Do not introduce any additional oil to the cylinders before performing the cold compression test. If you did the pre-oil procedure, there will be more than sufficient oil film to create a ring seal for a cold compression test.
If compression numbers are way low or just "low" you can scruu around for hours trying to determine "why"...but at that point who cares??? The motor needs to come apart and be refreshed, including all that goes along with that scenario. Yeah...ya could find a blown head gasket but if the motor has been running with coolant in the oil, it needs attention internally, so band-aiding a head gasket is a waste of resources.