850 cfm proform carb on 318!!!!

Small Block Mopar Engine

  1. T67POWER

    T67POWER Well-Known Member

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    I feel like a mad scientist.......................:glasses9:
    I am selling my 750 double pumper on my 318 cuda and will be installing a 850 proform carb.
    Why would i try such a foolish thing ........................

    I am basing this on David Vizards testing done on a 383 chevy.

    He installed three different carbs flowing.......

    740 cfm
    920 cfm
    1030 cfm.

    The 1030 cfm carb made the most horse power and gave up NO torque down low in the rpm band.
    This goes against all traditional thinking but it worked for him.

    The reason it works-- according to Dave -- is due to the carb being installed on a two-plain intake.
    The carb only sees half the engine with a two-plain intake (180 degrees)

    Dividing 1030 cfm by 383 cubic inches = 2.6892
    2.6892 x 383 cubic inches = 1029 cfm

    This is the percent ratio I did for his test comparing cubic inch to cfm.

    ----------------------------------------------------------------------
    Dividing 850 cfm by my 323 cubic inch engine = 2.6315
    2.6315 x 323 = 849 cfm

    My 318 bored .030 over = 323 cubic inches.

    It has adjustable idle feed jets so i can lean it for the small cubes.

    My 318 is gonna love this thing.=D>
    I have a 3000 converter and 3.91 gears so she will sing up high for sure.

    This 318 is begging for the 8 3/4 I'm getting with 4.56 gears and slicks.

    [​IMG]
     
  2. swinger340

    swinger340 Well-Known Member

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    Everyone laughed @ me when i put an 850 on my 340 but she loves it.
     
  3. oldkimmer

    oldkimmer FABO Gold Member FABO Gold Member

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    ............1st off a 318 bored .030 is not 323.....u do not gain 5 cube on every engine bore .030.......just saying........eg a 327 chevy bored .030 is a 331......only a 4 cube gain......kim.......
     
  4. Johnny Mac

    Johnny Mac www.blueprintengines.com FABO Vendor

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    it's a rule of thumb, who cares? the famous derogatory one sentence post thats on countless topics on here that in no way relevant to the original question........annoying.........

    now to address the topic at hand, i had a build 318 that loved a 750 double pumper vs. and edl 600..just remember u can only throttle screw lean it so much because the the CFM of air will be the same, i assume the motor is pretty built since you wanna go THAT big, but i agree, for some reason the modified 318 in my experience has always liked a biggish carb vs smaller.
     
  5. rumblefish360

    rumblefish360 I have escaped the evil Empire State! FABO Gold Member

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    Yes ol-kim, small potato's and no help.

    T67, yes and no and heres why.


    First up, it is a build dependent item.

    2nd, it's a area where a larger carb could stink on the engine. You allready descriobed certain things about the engine that can have this work.

    However, things like stock stall converter and a 2.76 rear gear etc.... would have this a real pain to tune in and work well. While possible, it's hard to get a 850 to work. I have and I didn't like it much. Then again, my stock verter & 2.76 gear were not helping the issue.

    David Vizards results are acurate. This I know first hand before I knew who he was. BUT, the engine and car set up has to be able to handle it first.
     
  6. MoparAnglia

    MoparAnglia Well-Known Member

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    Err, yes it IS a 323. You probably should have done the math before leaping into that one.


    3.94 bore and 3.31 stroke gives 1.97x1.97x3.1426x3.31=40.37cubes per cylinder. Times that by 8...

    Oh, and the 327 +.030 comes out at 331.75 - I'd call that 332 (anything over 331.5...)
     
  7. moper

    moper Well-Known Member

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    What kind of conventional thinking does it go against? The reason the generic formulas are used is because on a street car, where engine speeds and throttle opensing are all over the place. The bigger cfm will always make the most horsepower. And at full throttle, they won't give up much. It's not as mnuch about the 50% "seeing" but rather the fairly steady throttle opening and ever-increasing rpm (until shift point is reached). I think what you will find if you run a wide band O2 is that at low engine speeds and part throttle, the big carb can't mix fuel well. So the response is sluggish, the mileage sucks, the plugs get fouled earlier, the idle isn't as controlable or good, and the smaller carb would work better. Pretty much any drag race engine will do better with a typically "overcarbed" situation. Street cars don't.
     
  8. T67POWER

    T67POWER Well-Known Member

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    Moper........
    Normally I double the cube to get the cfm requirement.
    (conventional thinking)

    This is on a single plain intake that pulls the complete carb cfm.
    For example: I use a 750 holley hp on my 360 with a M1 single plain intake.
    360 x 2 = 720 cfm.

    I can also try the 850 on my 360 at some point i guess.
    My 400 big block ,when ready, will get the new 850.
    The 400 is using the new victor 383 intake (single plain)

    Just trying to improve my choices while keeping the cost down.
     
  9. rumblefish360

    rumblefish360 I have escaped the evil Empire State! FABO Gold Member

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    Conventional thinking? Equals conserveitive thinking and it's geared towards a street car with or without performance items added on. Nothing to hot as a driver. For best street manors and drivabilty and mileage concerns, the small carb is fine and very workable even if theres an upgrade in the performance add on's.

    Doubleing the engines C.I.D. for daily grand-ma street driver to high performance runner is OK and fine.

    More built up engines can go beyond this idea and leap up in CFM like ytour about to do.
     
  10. Dustedu2

    Dustedu2 Well-Known Member

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    Should I slap a 1050 on my 422?
     
  11. Johnny Mac

    Johnny Mac www.blueprintengines.com FABO Vendor

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    you're exactly right, i ran a 318 in a race car with my car number (323) for years
    ignore....that...guys....posts....he is annoying...and unhelpful .............johnnymac........... ............ ........ lol
     
  12. john_the_great

    john_the_great Active Member

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    The only reason I could see a big carb causing problems is if it was combined with big valves and big ports, may create a little bog off the bottom. But with a two-plane manifold you should be good, i really enjoy David Vizard's books. :)
     
  13. green1

    green1 Well-Known Member

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    Look up what, say, a 350 ci needs; anything over 550 carb slows it(street)
     
  14. 64physhy

    64physhy Well-Known Member

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    A 950 would do it some good. I run a Holley 950HP on my 414.
     
  15. yellowdartdave

    yellowdartdave RIP 1-5-12 Legendary Member

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    Small potatoes.................


    [​IMG]
     
  16. toolmanmike

    toolmanmike Moderator Staff Member FABO Gold Member

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    Cool old photo Dave. Back then the 4 barrels were probably around 550 cfm and 4 would be around 2000 cfm. I'm sure a 13.5:1 426 wedge could easily handle 2000 cfm. Dual Dominators? No wonder why they invented them. Those 4 carbs have got to be a chore to tune and adjust. toolman
     
  17. moper

    moper Well-Known Member

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    Sure. My 4" engines start with a wet flowed 870. the one on the stand now will idle with a little romp at 800rpm. I forgot who it was but somebody said the larger the carb the faster the car went when talking about a race 410 on the track. It's the truth. But try to get that 1050 to idle clean and transition to part throttle smoothly...lol

    The reason the carb size is important has to do with the reaction of the fuel to the air flowing thru the carb. The signals created by that motion are what makes any carb work. When the airflow is impeded the least (full throttle) and generated the stongest (mid-high rpms) those signals are strongest and clearest and the results are the best mixture you can get with a carb. I don't think I have a system for choosing anymore...lol.
     
  18. plymouth67

    plymouth67 It be a lot cooler if you did...

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    Is the 750 maual or vacum secondaries? How much?
     
  19. T67POWER

    T67POWER Well-Known Member

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    plymouth67........

    My 750 is a holley double pumper with a manual choke.
     
  20. john_the_great

    john_the_great Active Member

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    mechanical or vacuum secondaries?
     
  21. T67POWER

    T67POWER Well-Known Member

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  22. plymouth67

    plymouth67 It be a lot cooler if you did...

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    thats what i meant. and how much?
     
  23. Bad Sport

    Bad Sport HALF A BUBBLE OFF Staff Member FABO Gold Member

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    That's what I came up with.

    "bore x bore x stroke x .7854 x # of cylinders = cubic inches, then 3.94* 3.94*3.31 *.7854 * 8 =322.85 c.i.-so sounds like you have a"323".
     
  24. T67POWER

    T67POWER Well-Known Member

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    67plymouth.........
    I am selling it for $350.
    I am working on a road runner soon and will be giving him the carb with a tune up.
    I am also selling the fuel line and a four hole spacer to him for extra.

    He had three different people work on it and they could not seem to get it running right.
    His carb is junk and i know mine is good.
    It's a older 750 double pumper that i used as a bracket carb.
    I heli-coiled where the bowl screws go on the main body because they striped out from all the jet changes over the years of racing it.
    I will set the carb up for who ever buys it.
    At the moment it's sold,but you never know what the weekend will bring.
     

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  25. DusterKrazy

    DusterKrazy Well-Known Member

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    IIRC, a '71 340 comes with an 850 Carter from the factory. So jokes on them!!
     
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