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Holley Model 4175 "Q-jet Replacement" Carb Experiences

Discussion in 'The Venerable Q-Jet' started by Dan Gerber, Jan 23, 2007.

  1. Dan Gerber

    Dan Gerber Founders Club Member

    Does anybody out there have personal experience with a Holley model 4175 (p/n 80555C) "Q-jet Replacement" spreadbore carb? I'm considering replacing the custom late-model (i.e., '78 and later) Q-jet on my Buick 350 with the Holley for ease of maintenance, familiarity of local mechanics/tuners, etc.

    Now I understand that the Holley is only rated at 650 cfm (as opposed to a Q-jet 750). I'm quite sure that I'm not using the full capacity of the Q-jet, anyway, since I have ported cast-iron manifolds instead of headers. That is, I suspect that the exhaust manifolds will be the restriction, not the carb.

    This particular Holley carb uses the Q-jet bolt pattern, ahd has larger secondaries than primaries, so it is a real "spreadbore" carb.

    Anyway, has anyone had experience with that particular Holley carb?

    Hearing about your experiences will be greatly appreciated.

    Thanks in advance,
    Dan Gerber
    Anaheim, CA
     
    Dan Gerber, Jan 23, 2007
    #1
  2. BadBrad

    BadBrad Got 4-speed?

    Dan,

    I used that carb from new back in the late eighties on a 455. In theory a large enough carb for the 455; in practice it would go lean at high rpm as the fuel couldn't keep pace with the very rapid air flow.

    At all other engine speeds I found it to be a great choice.

    I think it would be a fine choice for a 350.
     
    BadBrad, Jan 28, 2007
    #2
  3. mummy68

    mummy68 Silver Level contributor

    "Q-jet" Replacement car question

    hey Guys
    I'm restoring my skylark and the carb is broken. I need to get a new one my engine compartment has a lot of chrome So I was thinking about the q-series. I have a 72 convertanle 350 engine 2bb. Does anyone know the correct model
     
    mummy68, Apr 18, 2009
    #3
  4. doc

    doc Well-Known Member

    Dan,
    I did the same thing on a 1970 455 stage 1 and it worked very well, but I could tell that the engine could use more carb.... Holley did make a 800 cfm version of the spread bore.... I find the holley to be very tunable, reliable, and easy to work with.... the factory stock qjet is rated at 750 to 800 cfm.... if you reduce the cfm s by that much you will be able to tell a difference in the performance... quite a bit of difference... Buick engines like big carbs any way and reducing the size is not the way if you like performance.... Like Brad says , all carbs will lean out at high rpms... so the combination of smaller fuel/air flow and carb lean out at high rpms will really affect the performance.... but the gas milage is probably good... I picked up 3 mpg.... went from 10 mpg to 13...:laugh: :laugh: if you put the bigger version on that engine, you probably will be happier...
     
    doc, Apr 19, 2009
    #4

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