From SCC they talked about how to approximately precentage wise calculate how much more fuel is needed when adding a turbo..but what about oging from one turbo to another? 7psi of a small turbo is going to push less air than 7psi of a larger turbo..

But it is probably based on how much CFM you are moving and through how many cylinders.

then see what kind of percentage increase that is over the last turbo. Then you can get injectors that are the same percentage larger than what you have now.

Eg..

You are flowing 30% more mass air with new turbo.

Get injectors that are 30% larger and probably an adjustable FPR and thats a good starting point.

try using this calculator...
http://www.rceng.com/technical.htm

aaron