So guys do any of you know how much compression the 800 came with stock? I have 120psi know. My friend has a 00 thundercat and he has 125psi.

Sounds close, the T-Cat has bigger bore with the same stroke and may
show a slightly higher reading and probably less miles, I wouln't worry
about the difference. :)

120psi after break in. :D

So 120psi is lost of compression? What did they come with new like 135 or 140?

125-130 new, until the rings seat. Optimum is 120-125psi.