So I'm going off a 2005 Legacy GT here but I think the stock injectors are like 550 cc or something like that.. I was wondering is the injector duty cycle and size play a role in it? Like say you switch out the 550's for 850 cc injectors it's going to already flow more then stock or does the IDC play a part in it as well?

Injectors are generally flowed at 80% of their capacity so if you crank up the IDC to 100% you could flow 660cc out of a set of 550's

 

An 850cc would flow 850cc at relativly the same IDC as a 550cc, you would need to adjust the IDC to compensate for the extra fuel in idle and cruise conditions