Everton Pabon

I'm using a 2007 CZAR 175mm crank with 18/16 gear. ZOO! Piranha frame: wheel base: 1098 mm BB high: 45 mm chain stays: 383 mm head angle: 72 graus (I'm 1.78cm tall) There is some text explaining how to calculate/find the correct stem? I would like to understand how this works..

Hey! I have a Zoo! Piranha (long frame) and I'm trying to find a stem. But all I tested (the last was number 4, 150mmX30º), I feel like the front of the bike got too heavy. Someone could tell me which stem is ideal for this frame? Thanks for the help.