550cc is good for 300whp. and you will need a walbro 255lhp fuel pump. again, all this has been covered. if you just use the little search button you will find any info you need.
for yourself.. 300hp like it says above 550cc are fine. if you plan on wanting to eventually break past the 300hp mark, get some 800cc injectors and tune them down.
i have a Turbonetics GT35R with 1000c.c. precision injectors, AEM FPR, 255 walbro pump and stock gsr fuel rail.