Fast Idle RPM'S ?

Engine, Trans & Driveline

  1. 1STMP

    1STMP FBBO Gold Member FBBO Gold Member

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    Hey all, at a loss as this is my first big block
    Mopar build.
    What should I set the fast idle rpms to.?
    The factory settings on the 750 cfm quick slayer
    put the rpms close to 2000. To my ear, this sounds
    way to high, and I'm getting slight lifter rattle on
    cold start. The 440 is basically stock, w/50
    psi cold. Cam is 230/230 at .05/480 lift/109lsa.,
    727 trans, 2800 stall conv. Warm idle- park-= 900
    rpm/in gear=600rpm. This engine is barely past
    break-in and has not been driven as of yet.
    Thanks in advance for your valued input.
     
    Last edited: Nov 26, 2021
  2. 66Satellite47

    66Satellite47 FBBO Gold Member FBBO Gold Member

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    IIRC, I'd set it in the 1500 RPM range. That should be enough to keep it running.
     
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    • 72sunroof

      72sunroof Well-Known Member

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      Fast idle rpms are set warm. When you start it it will take time to get there when it gets there it is warmed up. No harm in 1800 rpm fast idle it just speeds up warm up.
       
    • Ron H

      Ron H FBBO Gold Member FBBO Gold Member

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      Have mine set at 1200 RPM fast idle. Old school tips from old mechanics..
       
    • 440+6

      440+6 FBBO Gold Member FBBO Gold Member

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      1200 fast idle, never for long becouse I'm driving within 5 to 10 seconds later, never stalls either.
      725 for low idle, 440 six barrel.
       
    • Don Frelier

      Don Frelier FBBO Gold Member FBBO Gold Member

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      The 300 rpm drop into gear seems a bit high?
      I would think it should be around 1/2 of that or maybe 150 RPM.
      Have you done any tuning on it?
      Try a higher initial advance if you haven't already like 15-20 Deg. BTDC.
       
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      • Nate S

        Nate S Well-Known Member

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        2000 seems high. There’s no real “right” here. Depends on what you want. I never even bother with a choke, I start it and hold it around 1200 for half a minute then it idles at 750 after that. I guess if I had a choke I’d aim for about the same. Like you said, it’s not a huge cam so it shouldn’t need a whole lot.
         
      • Billccm

        Billccm FBBO Gold Member FBBO Gold Member

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        Ol'Richard Ehrenberg recommends 2000 for what it's worth.
         
      • Jc cooper

        Jc cooper Second gear fun! FBBO Gold Member

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        Not convinced that a cold engine should run above 11or12 fast idle , mine likes 850 rpm warmed up with my set up !
         
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