2.55 upper is 13psi. proabably ~550-560whp.
most people don't do just the upper alone. some people have done just the lower 10% pulley which was 540-550whp. that is 10.5psi or so
my .02 if your pulling the snout to do the upper port it and throw a TB on at the same time.
then when you get done with all your mods you will be in the 600-625 range you will need injectors too at that point as you will be out of duty cycle.
2013 ZL1 (president of the tangent oregon trophy husband association, founding and only member)
2013 Megacab 8" lift 38"mt's