base gaSKET THICKNESS

Discussion in 'The Venerable Q-Jet' started by agetnt9, Sep 26, 2013.

  1. agetnt9

    agetnt9 Agetnt9 (Dan)

    How thick should the Q-jet base gasket be for a 72 350 4bbl GS ? Summit sells all kinds:Do No:
     
  2. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    I use the 1/4" one. The best IMHO. It isolates the carburetor better from intake heat transfer, but if you have the exhaust cross over open, it doesn't matter much.
     
  3. Gary Farmer

    Gary Farmer "The Paradigm Shifter"

    I read somewhere that someone stacked two 3/8" to get 3/4" because with no spacer, the size of the rear secondary flaps dip down into the plenum and hinder reversion flow.

    Personally, I would use a (1") 4 hole spacer on dual plane and combo spacer on single plane, with regular paper/fiber type gaskets and/or an insulator gasket for sealing the divider in a dual plane case on lower-end engines, depending on the combo.

    If what you're looking for is insulation from heat, I hear the phenolic spacers do a good job at this, and can be had in thicknesses as thin as 1/4" I believe.

    I read that phenolic plastic can withstand up to 300* Fahrenheit, is relatively inexpensive compared to other spacer materials (such as aluminum), and is about the best you can get for heat transfer resistance and durability.
     
  4. agetnt9

    agetnt9 Agetnt9 (Dan)

    Well, just thinking about the ram air cleaner, and how that will be affected height wise.
     
  5. Gary Farmer

    Gary Farmer "The Paradigm Shifter"

    I read here on the forums that you can use up to a 1" 4 hole spacer and still use the GS ram air cleaner with clearance under the hood, you just have to cut the foam rubber seals down a little.

    So 1/4" would be fine with no modifications, I would think.
     
  6. agetnt9

    agetnt9 Agetnt9 (Dan)

    Cooooooooool,,, But the bracket that holds the cleaner up would be to low, right?
     
  7. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    If it is, all you need to do is glue a piece of rubber to the top of it, or the contact area of the air cleaner.
     
  8. Cliff R

    Cliff R Well-Known Member

    The correct OEM gasket is 4 hole and pretty thin on those, probably about .120-.130". A thicker gasket can be used, but the choke arm may end up needing some adjustment, or a longer one made if you are still using the factory divorced choke set-up. Use caution when using anything other than the factory gasket on the 71-74 Buick carburetors, as it may not cover the void where it provided vacuum to the secondary choke pull-off, and will have a vacuum leak. Spacers and double stacking thick gaskets for near stock applications is a complete waste of time/funds, and just mandates some "cobbling" to get the choke and other items hooked up and working correctly. You aren't chasing around enough power for all that effort. My car runs nearly into the 10's in full street trim with a factory intake, carb, and stock gasket. I've swapped on 1" spacer, 4 hole, semi-open, fully open, and fully divided at the track on back to back runs. The car runs the quickest in ET with one stock gasket, and slowed down in 60' with all other combinations. I did see a slight MPH improvement with a semi-open 1" spacer, but the car still ran slower in ET. Keep in mind this testing is with a 455 that has 11 to 1 compression, .635" lift roller cam, and custom ported aluminum heads. Going thru all that testing with a 350 engine is just wasting time, the effort is better off spent elsewhere....IMHO.....Cliff
     
  9. agetnt9

    agetnt9 Agetnt9 (Dan)

    I bought your book and have a 7044244 carb that is off a 355 and want to put on a 445 engine with a little bigger cam and bigger exaust valves and headers. Can U give me a start point as far as the jets and rods?
    I made some of the air blead mods in base to start small first.

    Inlet tubes are .036
    chanel restrictor is .059
    Base plate air bleads drilled at .059
    Air horn bleads look to be about .036
    Jets are 72
    Rods are CZ
    Metering rods at 46C
    Dont know if that was what was in there factory or not. Had a hell of a time getting the little inlet tubes out but did:eek2:
     
  10. Cliff R

    Cliff R Well-Known Member

    72 jets would be HUGE in a 244 carb if it has the tiny MAB's in the airhorn. I leave all the airbleeds at the stock sizes in those carburetors, just modifying the idle tubes, idle bypass air and idle down channels for the application. I prefer to keep the 68 main jets, then add an external APT screw and use our 42 metering rods in them. I go richer on the secondary side as well......Cliff
     
  11. Gary Farmer

    Gary Farmer "The Paradigm Shifter"

    I can't foresee any of those spacer combinations tested resulted in anything but power loss when used on a 4 hole stock manifold.

    When using aluminum heads, the stock intake won't get hot enough to warrant any sort of insulating gasket, and any spacer other than a true solid 4 hole spacer would cripple air flow into the plenum, since it would create a break in the 4 holes leading to the plenum. THIS is why no spacers or insulating gaskets are needed on a 455 with aluminum heads using the stock intake manifold, because incorrect spacers will actually hurt performance.

    Cliff's combination isn't the same as a Buick 350, but whatever. I don't have a 10 second car and therefore have no clout to back up my scientific theories or statements other than a logical explanation as to why something is the way it is. Changing conditions in the weather will have more of a power impact on Cliff's engine than a spacer ever would because 10-15 HP on his engine is nothing compared to its total. The ratio is smaller than 10% extra humidity in the atmosphere or 200 extra feet in elevation.

    You won't kill your car by putting on the factory gasket, and it will save the trouble of all this back and forth and disagreement.

    Best wishes.
     

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