i go for speed only and my ranking is pretty good

I went back to improve my Feb games on speed; but the ranking went down. I understand the first 33 games weight more than previous games. However; I don't understand why they don't let us to understand the ranking program in details.

You're saying your ranking improved when you improved games earlier then the last 30 days or were you saying it got worse? The problem with the explanation for the ranking system may be that it's lost with Adam the author of this site who no longer is involved. Without digging into the programming, Qhermit may not know since all we have from Adam was some brief explanations what he was thinking of doing. Once he changed the ranking system for the last time he never gave a full description of how it was calculated.

I guess I am lost in ways that the new rules are not transparent.

One thing clear about the score is that if you go back to improve old games (speed particularly), your score will drop. I found this out the hard way, so do not do this.