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Join Date: May 2008
Location: Orange County, Calif
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While trying to final tune my 426 Jeep, I have been to more injector sizing sites than what should be allowed. It seems that all injectors are rated using a 43.5psi fuel pump rating. That makes it difficult to figure out what is needed or the formula for our 58psi fuel system. Once you cross over into bigger cubic inches or forced induction you need to size a larger injector. The downside is loss of quality idle, drivability and long and short term fuel trim. Well until a tuner can SIZE the injectors into the tune....and even then I havent seen one that idled perfect!
Based on wheel horsepower and roughly a 20% driveline loss for a Jeep I had to swag the crank horsepower...so,
For a crank horsepower of;
580hp.... a 45.3 lb/hr or 475cc/min injector is required.
600hp.... a 46.88 lb/hr or 492.19 cc/min injector is required.
680hp.... a 53.13 lb/hr or 557.81 cc/min injector is required
38lb injector @58psi = 43.8 lbs/hr
40lb injector @58psi = 46 lb/hr
42lb injector @58psi = 48.4 lb/hr
50lb injector @58psi = 57.7 lb/hr
Out of curiosity I looked up the smallest SRT4 injector which is the
2003 SRT4 injector, rated at (43.5psi) 47lb/hr @ 58psi = 53lb/hr or 557cc/min.
2004 SRT4 injector rated at (43.5psi) 52lb/hr @ 58psi = 59lbs/hr or 577cc/min.
I wont even touch the Stage 2&3 injector rating.
Clearly the 2003 SRT4 injector is a bit overkill unless you are making well over 680 crank horsepower.....and at that point good luck with idle and streetability.
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