That is them running at 100% duty , but I have to say would think if everything else is right like intercooler and fuel pump you might find 21 psi is enough in it , but at least they should give you some " headroom " in case you want to go to 26 psi , if you are looking at not running injectors flat out but more towards 80% you would be looking at 450cc so the ones you got are somewhere between the two .