Sorry for being a bit dumb in this area but ive never needed to know but what are air injectors?

and can anyone tell me what sort of power i could get from a cossie if its running a hybrid t34 .48 housing, big custom intercooler, ported head, 3bar map, 4x4 pistons and either blues or greys depending on what my turbo could keep up with?

thanks in advance. darren.