I was reading in the hanyes manual that if you unplug the vac hose of the FPR, It states with the hose on it's 31-44PSI with it unplugged it's 42-50PSI. If I were to plug off the vac line with a screw or something like that and leave the FPR unplugged would it give me anymore performance? Or is it something I should just try out down the track and see if it's good or bad?

2009 Ford Mustang V6
No don't try it down the track or at all.
let me help you think logicly about this
when the FPR is unplugged from vaccuum it see's atmospheric pressure (the same as WOT). so your turning the pressure up at all times.
meaning now you stock injectors that flow 19lbs/hr are going to flow a tad bit more, meaning your going to run rich at all times, even when its not needed. If you have minor bolt ons, their is probably not much more needed fuel, even at WOT, let alone anywhere else.
you probably wouldn't see any gains at the track because when you are WOT, its just like have the FPR unhooked, because it is seeing atmospheric pressure. So no performance gains will be seen.
I will chime in on this. From personal testing of this. As state it will increase fuel pressure. Can it add power?? Well it could if certain things are inline. Testing on 2.4 cars. 2 2001 Z24's and 1 99Z24 with a 01 motor. Also 2 were auto's and 1 (mine was manual). The auto's did gain about 1 tenth in the 1/4. Mine no real difference. Now seeing as our cars run rich from the factory adding more fuel is not really needed. In my case I need to take fuel away. Every car and every set-up is different, and your car could be lean, but without a wideband you will not know. Also as stated when racing you are at WOT anyways, but I could see a small edge to haiving fuel there already, but only if the extra fuel is needed.
FU Tuning
OK thanks thats all I was wondering.

2009 Ford Mustang V6