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Can someone please point me to normal compression test values for a 1931 Packard 840 (super 8 engine)? I’ve seen a couple of forum posts on the internet suggesting 80-85 as normal, but I can’t find an official listing. Thanks!

This should provide the answer.

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Dave, I'm surprised altitude has that much of an effect on compression?!!? It makes sense that it would have an effect - but a couple of thousand feet sure brings it down a notch! Chris.

The Packard manual specifies 85 psi through 1931. They raised it to 100 psi in 32.

Rule of thumb doesn't always work. For example, I had a modern car that always had 165-175 psi for 9.9:1 compression and the manual specified 200 and said anything below 180 was a sick engine. I bought the car new and the engine quit at 112,000. I later found out from an engineer that they were using junk rings for the American builds. The Mexican builds were going over 700,000. If only I was in California when I bought it!

Back to rule of thumb: Generally, an engine will lose 3% horsepower for every 1000 feet above sea level. Which always has me thinking about a publicity photo of a Packard 120 seven passenger fully occupied and climbing Pike's Peak. That means the car was only putting out 70 crankshaft horsepower at the summit. That picture has me thinking that all the overhauling in the world will not restore as new performance in old motors.

Thanks to all!
I’ve got problems- hopefully it’s just valves that can be adjusted, and cylinder 1 likely with a ring issue.

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Looks like some stuck valves. Pull valve cover and check the action.

The one wet test indicates ring problems, but they may be stuck as well.

Not surprising if you think about it. You need oxygen above 10000 ft, so the ratio of fuel/air has to change going up. Planes adjust, cars aren't equipped but usually tuned for altitude if they reside at elevation.
The compression ratio isn't always correct. Best to calculate or measure as head space varies with design /overhaul. The L flat heads have a larger head space so lower compression by default.
Use it as a guide, if they're all over the map then there's problems, if fairly uniform, good to go. I would not get bent out of shape, if my numbers did match to book values, because you probably did not correct for air pressure, temperature, etc. which you need to do. Log what you got by vehicle and keep for reference next time.

I have lots of documentation on the car which was originally restored by Nethercutt around 1960- Here’s an Allen-Tronic evaluation that I believes dates to that period, although no specific date is listed. Page two lists compression test results at the time- mostly 60-65 psi, and check boxed “ok”-interesting.

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Page one of Allen-Tronic report

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I’m thinking about filling the zero compression cylinders with Marvel mystery oil or penetrating oil and letting them soak to see if I can get the stuck valves to loosen up. Any thoughts or recommendations?