I don't know how to factor in altitude but when I did a compression test on my 350 I was getting 170-180 readings except one cylinder was down to 90 so I swapped in a 454 and left the SBC world behind me never to return
Nothing like a stump pulling low RPM 454 RAT!!
YYYYYYEEEEEEEEHHHHHHHHHHHAAAAAAAAAAAAAAAAAAA!!
Sorry a little too much
for me today! hahaha