Re: 1979 mercury thunderbolt (pressure)
Won't find a max spec on compression anywhere. There are alot of factors that determine the reading and that makes it hard to assign a number.
Most manuals won't even give a typical spec. More important is the uniformity between cylinders. A motor will run well at low compression if all cyls are the same, but the same motor with some cyls at higher and some at lower compression will run like crap.
Generally accepted rule is that all cyls should be within 10% of each other.