The size injectors you get are dependent on a few things. 550s are good for up to 21 psi on any turbo w/ 93 octane. YOu can actually run 550s up to 26psi on 93 octane and AFPR. 550s are more then enough injectors to do the job if you have available fuel resources. Now if you only have up to 91 octane then you should go with 660cc beyond 19psi. People think the size of the turbo matters when it doesn't, it is the amount of boost that matters.