Its not only upvotes that affect ranking, but also flagging.
Because time is involved. The scoring formula is something like `(votes/age)^g` where `g` is a "gravitational constant". So if there is a post with 200 votes overall but is 20 hours old will be ranked lower than a post with 30 votes but was created 1 hour ago
Are you sure that formula is right? f(x)=x^g is a strictly monotonic function for all positive g, so the ordering of the scores will stay the same no matter what constant is used for g (assuming g is positive).
It's a bit more involved than that. There are factors like nonURL posts etc. It's been some time since ycombinator.com/arc held the source code of HN (it no longer holds the source code) so I can not verify the actual formula.