This actually clears some stuff up for me too. With the GIAC tune, their k04-02x sotware, I was running the 225TT's maf and injectors because they were a requirement of the tune. After starting to do a little tuning here, it is now clear to me why GIAC would make those requirements in a tune. 'Cause they are lazy bastards and just took their base maps from the stock 225TT tune. I didn't realize that the 225TT was a 3bar. Makes sense why GIAC didn't require a 4 bar FPR. duh.
So should I stick with the 3 bar or would it benefit to use a 4bar?
If you feel like spending the time to tune for the 4bar go for it. You'll get slightly better atomization and the injectors will be able to overachieve the rating of 386cc@3bar but not by much. What I mean by "not by much" is say you are running 3bar @386cc and you raise the pressure to 6bar effectivaly doubling the pressure, you'll only gain 1/3rd the total original flow.
Your pump will have to work harder all the time also and you'll find that the stock pump won't be able to keep up at higher rpm. That may even happen @ 3bar especially if its old. I assume if you can find a pump that drops in from a car that came with the 4bar reg then you'll be alright for the most part but you may as well go aftermarket.
As far as GIAC being lazy, I don't think so. They are selling a base map "safe" to flash and if you can get to one of their dealers and spend lots of money dyno tuning they'll go the extra mile and custom tune your ECU for whatever mods you have or want. Same thing with the other big name tuning companies. They all offer custom tuning of their software you just gotta go there or rent their hardware used to flash files to your ECU in some cases.
