im new to these cars so would like to know when id upgrade to this size injector? my car has turbo elbow, full exhaust, front mount,air filter, and turbo timer, so may be up to 300bhp? would these be better paired with an uprated fuel pump?
It won't be 300bhp with that list of mods mate. You'll need to be running about 1.1 bar of boost to be near 300bhp. Take a look at this from the useful threads. It's only a rough guide as far as the power outputs go, but the mods list is good showing the different stages.
I you won't need these yet BTW unless your planning for a remap + more boost.