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Flathead Intake 4x2..IRs

Discussion in 'The Hokey Ass Message Board' started by strombergs97, Oct 17, 2009.

  1. strombergs97
    Joined: May 22, 2006
    Posts: 1,888

    strombergs97
    Member
    from California

    OK, Matt at Gear Drive has a 4x2 intake (staggered) that is IRs. Looks like the runners, one for each cylinder. Only half the carb supplies the air and fuel?? A Stromberg 81, 135CFMs will deliver about 67 CFMs per cylinder????????
    Does this make sense?????????????
    Am I way off on this.HELP...
    Duane...
     
    Last edited: Oct 17, 2009
  2. Gemini EFI
    Joined: Jan 5, 2006
    Posts: 231

    Gemini EFI
    Member

    Hilborn flathead IRs have 1 11/16 butterflies. Our own flathead IR has 1 3/4 butterflies. All IR manifolds have bigger butterflies, due having a single cylinder drawing on them.
    GeminiEFI
     
  3. panic
    Joined: Jan 3, 2004
    Posts: 1,450

    panic

    Has to be muucchhhh bigger for IR.
     
  4. Flat Ernie
    Joined: Jun 5, 2002
    Posts: 8,406

    Flat Ernie
    Tech Editor


  5. strombergs97
    Joined: May 22, 2006
    Posts: 1,888

    strombergs97
    Member
    from California

    Thanks Ernie..I forgot about that one..That intake was a Lattin and the runners weren't seperated to each cylinder. The whole 97 or 81 would feed the cylinder, not just half the carb.
    Well, I think it will work just fine. The one thing I remember is that risers do help the flow but just how high of a riser..I guess that will be trial and error also..
    Thanks
    Duane.
     
  6. Flat Ernie
    Joined: Jun 5, 2002
    Posts: 8,406

    Flat Ernie
    Tech Editor

    General consensus is you'll need a lot more flow with IR.
     
  7. strombergs97
    Joined: May 22, 2006
    Posts: 1,888

    strombergs97
    Member
    from California

    Question, if I used a riser the is open not seperate runners the whole carb would feed the cylinder on demand???????
    Duane.
     
  8. Bruce Lancaster
    Joined: Oct 9, 2001
    Posts: 21,682

    Bruce Lancaster
    Member Emeritus

    Look over how the runners go.
    Stock '34-53, most common 2 and 3 carb manifolds...each valve sees half the carb barrels.
    Open plenum...carbs atop a "box" feeding all runners...each valve sees ALL of the barrels
    True IR...most flathead 4 carb setups are sorta/semi IR but seem to act like IR's...each valve sees ONE carb barrel.

    Hence...IR can use very large total carburetion, stock/180 manifolds can use more carburetion than the open plenum kind.

    I've discussed 4 carb flatheads with a few people, including one, Flatdog, who tried everything there was on his coupe before going to a blower. On his huge 300+ inch flathead, he felt he was undercarbed when he went to 4 97's from 3! That strongly suggests that the Edelbrock 4 type does function about like a true IR.
    SBC's with true IR, weber type setups, can tolerate way beyond 1200 CFM according to tests, on STREET engines.
     
  9. carbking
    Joined: Dec 20, 2008
    Posts: 3,292

    carbking
    Member

    To reinforce Bruce's comments about the necessity of much larger carbs with IR; we had an import with IR (with small pulsing connector tubes) FACTORY intake on a 121 CID 4 cylinder. Carbs used were two 500 CFM units. And no, it was NOT overcarbed! IR manifolds require a tremendous amount of carburetion compared to a multicylinder plenum type manifold.

    Jon.
     
  10. Interesting reading!
     

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