Rookie needs guidance for compression test

Don't pour too much oil or you could "hydro-lock" the cylinder, which could bend a valve or break a tooth on the starter wheel. Also, it would be cheating the test since displacing air volume. As people say, just enough oil to coat the rings. Sure the cylinders slant over, but so do a V-6 or V-8. Even my 4 cyl Dodge Aries engine slanted back a bit. Indeed, it was derived from the slant 6.

I agree that >100 psig is a minimum. I had a 70 psig cylinder in my 1969 slant once. The spark plug was always pristine since flushed w/ raw gas that wasn't burning. When I pulled the head, that cylinder was shiny clean metal inside and the walls showed deep scuffs from the rings.

The reason there is no exact value is that the camshaft and valve timing make a big difference. Some high rpm cams may show low cranking compression pressure because they only work well at high rpm and/or have much valve overlap for that lopey "race-car" idle that many desire, though runs like crap at low speeds w/ noxious fumes. Other cams may show >200 psig cranking pressure, which is bad because the starter must fight it. For a factory slant cam, 145 psig would probably be the "as new" pressure. It is for my 65 273 engine and I vaguely recall for a slant too.

I suggest you buy the Harbor Freight compression kit next time on sale (I got for ~$15.). Besides doing compression check, they have air fittings so you can easily connect to an air compressor. That lets you apply pressure at TDC and see how well the cylinder seals. If you hear a hissing leak, search for it. Past the rings blows out the PCV hole on the valve cover. Past the exhaust valves blows out the tail-pipe. Past the intake valves blows out the carburetor.

The poor-man's compression check is free and very instructive. Turn the engine over by hand, which you can do by tugging on the slant's fan belt (clock-wise as viewed from front). You should clearly feel 3 cylinders per rev. If you hear each one hiss down for >10 sec, the engine has excellent sealing. If you have ever kicked over a motorcycle, you will understand. I would also say tugged a lawn-mower, but many today have a "compression release" easy-start when tugging, for today's girly-man.