This is interesting. According to SCT the 21# injector was never used in a 96-04 Mustang 4.6l engine.
Then SCT is misinformed, my '03 had (I am running the FRPP M-9593-AA302 24lb/h units now) the "pink" injectors as do all very late '02 through '04 MY cars.
The Ford number is FOTE-9F593-D9B, Bosch 280-150-561, rated 22lb/h at 43.5psi, 21.1lb/h at 40psi--(40/43.5)^.5 * 22 = 21.1...
Here's a photo of one taken just now:
They may be basing their assessment on the low and high injector slopes in the tunes--Ford did not alter those settings in tha later tunes that I have observed. This is why the late '02 through '04 models run pig-rich at WOT, with AFR often dipping into the low 11's (11.2:1 or richer) at high load and WOT.
With the 21s I had to set the low and high slopes to 24.10 and 20.50 respectively (from 23.76 and 19.15 in the stock tune) to get the fuel trims in order and stop it from going rich at WOT.
Most canned tunes lean out the mix in the Stabilised Open Loop Fuel
table for this same reason.
- 2003 GT, UPR X, 24lb/h injectors, Magnaflow, 180° stat,
PP 70mm TB & plenum, Ralco RZ_flywheel, RAM HDX clutch, 3.73s, 262 rwHP/305 lb-ft.
new ride - 1998 SL500, 5.0L 32V 326/347 HP/tq