Typically you scan and see what duty cycle your injectors are at. Rule of thumb is to try and stay under 80%. At 100% they go static and stay open, no bueno if one sticks there.
Injector size = (HP x BSFC) / (number in injectors x duty cycle)
Horsepower limit = (Injector size x number of cylinders x duty cycle) / BSFC)
BSFC~.45-.5 from what I've found online.
HP=(25.2*8*.8)/(.5)=326.4HP@80% duty cycle
If you assume a .45 BSFC (more efficient engine)
HP=(25.2*8*.8)/(.45)=358.4HP@80% duty cycle
Copied from
How to identify vortec truck engine
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Fuel injector flow rate is very important to have programmed correctly in your PCM. Find a small 8 digit number located on side of each fuel injector. Here is the breakdown.
25317669, 25320287 - 1999, 4.8L and 5.3L - flows 2.742 gm/sec or 21.8 lb/hr @ 58 psi
25317670, 25320288, 25323974 - 1999-2000 6.0L, 2000 4.8L and 5.3L - flows 3.125 gm/sec or 24.8lb/hr @ 58 psi
25317628 2001-2007 - 4.8L, 5.3L, 6.0L - flows 3.180 gm/sec or 25.2lb/hr @ 58 psi
25326903 - 5.3L L59 Vin Z, flex fuel 5.3L - flows 4.164 gm/sec or 33lb/hr @ 50 psi
12554271 - 1997-1998 5.7L LS1 - flows 3.727 gm/sec or 29.6lb/hr @ 58 psi
12555894 - 1999-2000 5.7L LS1 - flows 3.438 gm/sec or 27.3lb/hr @ 58 psi
12561462 - 2001-2004 5.7L LS1, LS6 - flows 3.781 gm/sec or 30lb/hr @ 58 psi"
Billavista's LQ4 page
Vortec 6000 6.0L V-8 LQ4 Tech Article by BillaVista - Pirate4x4x.com