when you say they're running at 4 bar, do you mean they are currently, with a stock maf, or they will be when it's mapped?
if the car is currently mapped to a setup, and change on MAF or injectors will require a new map.
I would question why you're running a 4 bar though? unless you're running a turbo that takes the red tops right to their limit on 3 bar?
4 bar FPR's are generally bad news, as they put much more load on the pump. Avoid unless needed.