Re: Normal Compression Test Values for 1931 Super 8

Posted by Fish'n Jim On 2022/5/17 8:25:55

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.