Taken from cliffyks guide to bolt ons.
If you have the orange 19 lb/h injectors upgrading to the pink 21 lb/h units is worth the cost and effort. The 19 lb injectors are running near 90% duty cycle at the stock 260 fwHP output (flywheel HP). Ford realised this and changed to the 21 lb injectors in the late 2002, 2003 and 2004 MY production. Unfortunately they did not change the tune, which is why those models run pig-rich at WOT.
The 21 lb/h injectors run just under 80% duty cycle at the stock 260 fwHP.
At the top end of what can be expected from bolt-ons you may wish to consider 24 lb/h injectors as they will be operating at 80% duty cycle at 305 fwHP, or 260 rwHP--which is about the limit for the modest bolt-on modifications presented here. Operating at 80% duty cycle means they will be consistent and well-controlled, and provides reasonable headroom.
Sent from the mothership.