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Why 21 lb injectors...

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    Why 21 lb injectors...

    All the research I've done says to use a 29 lb/hr injector for an engine making 280hp (guessing the S54 with slight mods will make that much). Why then are the 21 lb/hr ones recommended by just about everyone?

    Even if it only makes 260 it should still require a 27 lb/hour injector...are the 21 lb/hr units driven that much higher in terms of duty cycle (80% is the industry standard)? At 80% duty cycle the 21 lb/hr injectors will only support about 205 hp....

    #2
    BMW motors are relatively fuel efficient from a BSFC perspective, and they run higher fuel pressure than injectors are rated for.

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      #3
      So it appears the BFSC is around .40, which would mean the 21 lb injectors are good for approx 260hp. That solves that mystery...

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        #4
        The fuel pressure makes a bigger difference.

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          #5
          Originally posted by matt View Post
          The fuel pressure makes a bigger difference.
          So then are these engines are especially susceptible to problems from dirty fuel injectors? I had mine sonic cleaned, flow tested and refreshed with new seals and screens before I put them in.

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            #6
            No, not really. BMW fuel filters are really kick ass.

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