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Over CFM on EFI N/A cars

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  • Over CFM on EFI N/A cars

    I have decided to go to the darkside and go EFI. Most EFI guys say put a huge CFM throttle body on it the mixture will be ok its EFI, this seems to be standard thinking, but I am not a standard guy : they may be right. Dont you still need port velocity to fill the cylinder, not for carb signal the EFI will do that but for the filling of the cylinder what do you all think is 2 1000 cfms threw 8 holes better or 2100 threw 4 or 1200 threw 4 for the air the motor pumps at a given RPM ? In this is a Tunnel ram better a Funnel Ram or a huge runner and plenum single plane ?
    2007 SBN/A Drag Week Winner & First only SBN/A Car in the 9's Till 2012
    First to run in the .90s .80s and .70's in SBN/A
    2012 SSBN/A Drag Week Winner First in the 9.60's/ 9.67 @ 139 1.42 60'
    2013 SSBN/A Drag Week, Lets quit sand bagging, and let it rip!

  • #2

    Re: Over CFM on EFI N/A cars

    Re: Over CFM on EFI N/A cars

    My understanding is harsh off idle throttle response when too large of a throttle body is used. WOT is fine though.
    Escaped on a technicality.

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    • #3

      Re: Over CFM on EFI N/A cars

      Re: Over CFM on EFI N/A cars

      I think he's asking from more of an airflow perspective. In a larger TB, the airflow will be slower through the "holes" than an appropriately sized carb. So the question might also be, "Is having properly rated CFM/airflow in an EFI TB as important as it is for a carb application?"


      He asked me via PM and I deferred to the smarter guys on here. I'm not an airflow wizard, I just make sure there's a proper amount of fuel, and spark at the correct time. ;)
      www.realtuners.com - catch the RealTuners Radio Podcast on Youtube, Facebook, iTunes, and anywhere else podcasts are distributed!

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      • #4

        Re: Over CFM on EFI N/A cars

        Re: Over CFM on EFI N/A cars

        That may be a better way of putting it. A well built N/A motor is all about air speed from the scoop to the CFM Carb to the booster in it ( this is fuel signal related, I think the EFI takes care of this part) intake plenum , runner cross section and length size of valve and Cam valve timing and all that goes with that. I think maybe the EFI can cover the signal and fool us into thinking more is better on CFM but if the air speed is down till it gets to the port all is lost maybe a sheet metal tunnel ram with a single big or two small throttle bodys may work well because the air signal is not critical and the long runner will speed air up if done right, I just thought I would see if 7 people out of 10 say no, I might try it LOL
        2007 SBN/A Drag Week Winner & First only SBN/A Car in the 9's Till 2012
        First to run in the .90s .80s and .70's in SBN/A
        2012 SSBN/A Drag Week Winner First in the 9.60's/ 9.67 @ 139 1.42 60'
        2013 SSBN/A Drag Week, Lets quit sand bagging, and let it rip!

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        • #5

          Re: Over CFM on EFI N/A cars

          Re: Over CFM on EFI N/A cars

          This might be a good read Jeff.

          http://www.camaros.net/forums/showth...ttle+body+size

          I think the consensus was bigger is better with the throttle bodies, but watch the intake and runner dimensions for wave tuning. Progressive linkage also seemed to be the hot ticket for low speed driveability.

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          • #6

            Re: Over CFM on EFI N/A cars

            Re: Over CFM on EFI N/A cars

            This might be relevant. I recently switched to individual throttle bodies on my 4cyl. I asked a fairly well known tuner about sizing. He came up with a size based upon questions of port flow, valve size, displacement, RPM and expected use. I asked about sizing and he said that it mattered to keep the velocity up from the entrance of the intake to the valve.

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