The lb/hr rating on injectors is what they're capable of flowing - not what they flow. They flow what they're told to flow by the computer up to (and down to) their limits. So even if the motor's stock, larger than stock injectors can be used provided the maf or computer are calibrated for the larger injectors. If the fuel pressure stays the same, the proper calibration simply allows the computer to keep the larger injector open for a shorter amount of time than the smaller injector under the same circumstances. So the same amount of fuel is injected by the 19 or the 24 if the cablibration is correct.
Where problems occur is when the engine is capable of moving more air than the smaller injector has the capacity to provide fuel for. That's when moving up in injector size will help things. Problems can also occur when a large injector is asked to inject very small amounts of fuel - for instance at idle.
So--24's on a stock motor can work just fine - but there's no performance benefit; 19's on a modded motor can work fine provided the mods don't cause the motor to require more fuel than the 19's can supply.
Similarly, if an engine is modded to where it wants to move more air than it's maf size will allow (in other words, the maf is the bottleneck to moving more air), than a larger maf will provide a performance benefit. If the maf is not the bottleneck, then moving to a larger one won't provide a performance benefit. Same is true with throttle bodies, manifolds, etc.
My car runs off more than ideas.
