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Docs dual plane mod

Discussion in 'Small Block Tech' started by Super Bald Menace, Jan 31, 2025.

  1. Super Bald Menace

    Super Bald Menace Frame off oil changes

    I've decided initially to run a factory 300 four-barrel intake and a Holley Terminator throttle body. One way or the other I have to open up the holes in the intake so that they are not creating turbulence or a restriction. Wondering if I should still leave it as a four hole or get rid of the dividers between the front and rear holes? As you can see the factory holes are smaller than the holes in the spacer which are the same size as the base plate holes in the throttle body. Will be a blow through turbo charger application Messenger_creation_1FF60D3F-4DF3-4CA6-B8CB-9924F6E4E664.jpeg Messenger_creation_7E3DF6CF-0F5E-422D-B00F-04A069D63416.jpeg 20250131_191448.jpg 20250131_191515.jpg
     
    TrunkMonkey likes this.
  2. TrunkMonkey

    TrunkMonkey Totally bananas

    Since your going to use the spacer and forced induction, leaving it a four hole won't matter after you open the holes.

    If you ever run it with the carb and no spacer, then it would make a difference with the blades being near/in the holes and removing the divider helps with the turbulence.

    You gonna tap and block the heat passages?
     
  3. Super Bald Menace

    Super Bald Menace Frame off oil changes

    The heat crossover passage under the carb will be blocked off and filled. TA heads don't have the exhaust crossover provision in them so I don't have to worry about them. I thought about going with a tapered adapter such as a super sucker or super duper sucker..lol
     
    TrunkMonkey likes this.
  4. Stevem

    Stevem Well-Known Member

    If you have the room a spacer deal like this will maintain the bottom end when there’s no boost being made but also pick up top end hp.
    With this set up the divider between the primary and secondary bores should be ground out.
     

    Attached Files:

  5. TrunkMonkey

    TrunkMonkey Totally bananas

    The divider on the intake is not going to be in play, or have much influence of flow/turbulence when a spacer is used and "blown thru" induction, as would be the case with a carb setting on the intake, where the throttle blades are in the airstream in the bores of the intake.

    In the latter case, having the divider removed, will be significant with normally aspirated application.
     
    Super Bald Menace likes this.
  6. Jim Blackwood

    Jim Blackwood Well-Known Member

    I wouldn't remove the divider. It separates the upper and lower planes of the intake and I don't think the manifold will work as it was designed to without it. Decades ago guys were playing with cutting slots in the divider, you might look up some of those old threads but the goal was to improve the top end and I don't think much attention was given to what it did at lower speeds and throttle openings. I seem to recall there were some intakes basically ruined in the attempt. Simply boring the holes out to match the throttle bores would probably be the best solution, maybe slightly larger to avoid a step.

    Those old iron intakes aren't exactly rare, but they aren't making any more of them and I'm pretty sure they made more of the 2bb ones to start with.

    Jim
     
    Super Bald Menace likes this.
  7. Jim Nichols

    Jim Nichols Well-Known Member

    I know if it was the aluminum intake you would open up water jackets and have to tig the holes up. The cast Iron intake you may open the heat riser port but I don't know.
     
  8. Super Bald Menace

    Super Bald Menace Frame off oil changes

    I would only be removing the portion between the lines. I think initially I will just open up the four holes to the same size as the spacer so there isn't a big step there to upset the air.

    20250131_191515.jpg
     
  9. knucklebusted

    knucklebusted Well-Known Member

    Could you get away with just chamfering the four holes to match the spacer? Might induce a little venturi effect. No evidence to support that other than my own thinking.
     
    Mark Demko and Super Bald Menace like this.
  10. Super Bald Menace

    Super Bald Menace Frame off oil changes

    I think that's where I'm going to start initially. It won't hurt the intake as far as I can tell. at the very least it should smooth out the air entry into the manifold
     
  11. Mark Demko

    Mark Demko Well-Known Member

    I would just taper that lip/edge and leave the rest alone.
     
  12. Jim Blackwood

    Jim Blackwood Well-Known Member

    Break out the old die grinder...

    Jim
     
    Super Bald Menace likes this.
  13. jmos4

    jmos4 Well-Known Member

    Hi,

    I thought I remember people using a 215 aftermarket AL intake with spacers on 300's. If you want to experiment might be a option.

    Docing the intake shouldn't have a big effect, but if it allows you to run the throttle body, go for it but check out the linkage clearance as had a few Holley carbs that need the spacer to get everything to clear linkage wise.

    Regards,
    Jim
     
  14. Super Bald Menace

    Super Bald Menace Frame off oil changes

    I have a Rover intake and spacers. I still have some work to do to adapt it and this will get me on the road sooner.
    20240803_151406.jpg
     
    patwhac and Max Damage like this.
  15. Super Bald Menace

    Super Bald Menace Frame off oil changes

    That's what I'm going to do initially and see how it works out
     
    Mark Demko likes this.
  16. Dan Jones

    Dan Jones Well-Known Member

    We've done some work with dual planes on the flow bench and tested the modifications on the dyno. This was for a Ford 351C but the principles should apply. First we tested the flow of a cylinder head, then we bolted the intake to head, along with a carburetor body wired open and tested each port again (both sides of the intake. What we found was that all of the older dual plane manifolds had 4 good runners and 4 bad runners. Generally, the runners were group by plane but oddly which plane was better or worse varied by intake. Sometimes it was the upper plane, other times it was the lower. Blending the runner inlets on the poorer flowing runners so they flowed as well as the better runners paid off on the dyno. Some intakes improved over 30 HP on a ~400 HP engine. On intakes with 4 hole bases, you have to mill them out to 2 ovals in order to get access to the runner entries. Depending upon the application, we might need to lower the intake divider for best results and we also tested several 1" carb spacers (HVH Super Sucker, 4 hole, open, etc.). If you look at the better dual planes (Performer RPM), they come with radiused entries and a lowered divider out-of-the-box.
     
    Super Bald Menace likes this.
  17. Super Bald Menace

    Super Bald Menace Frame off oil changes

    Ideally I would like to find one of the single plane aftermarket intakes for the Rover and use my spacer plates with those. I think it would suit my engine better but at this point I have two choices either the 4.2 individual runner intake or the 65 factory 300/4 barrel intake.
     
  18. Dan Jones

    Dan Jones Well-Known Member

    > I would like to find one of the single plane aftermarket intakes for the Rover

    You mean like one of these?


    Buick_Rover_intakes_06.jpg
     
    patwhac likes this.
  19. Super Bald Menace

    Super Bald Menace Frame off oil changes

    No wonder I can't find one. You got them all..:rolleyes:
     
    patwhac and Dadrider like this.

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