quick question

[suprra_girl]

LOL

well you are to the point aren't you

when you install 550cc injectors you now need to either drop them back using an safc or similar so you don't borewash the engine, run rediculously rich or even stall out from the richness
the engine doesn't know that there are 550cc injectors so it can't control them... so you then need something else that will invisibly input air or control airflow/injector duty somehow
this is where the lexus afm comes in
the lexus when installed allows 25% more air to enter the engine which the ecu doesn't know about either
so the invisible fuel and the invisible air end up matching each other and the air fuel ratio is once again even

550cc injectors = 25% more fuel than stock
lexus afm = 25% more air than stock

if you require any more info i'd be happy to help