I don't know whether this is a repost or not but i found this very useful when i was looking for a 35 shot jet for my dry kit and verified the sized with my local NOS dealer. Hopefully this helps out the community and is beneficial to someone. It does try to predict the loss of power through the drive train but i think it just takes a percentage and subtracts it from the HP to the crank. Also it tells you if your running a wet kit, what size the fuel jet should be while taking into consideration bottle pressure and fuel pressure.
N20 jet size calculator