Offenhauser Dual plane SBC
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Offenhauser Dual plane SBC

  1. #1
    Cpt. Millenium Falcon John Thompson's Avatar
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    Default Offenhauser Dual Port SBC

    Having a fairly mild 400 SBC being built for a 12J-C probably a B impeller. Shooting for 380 hp. I bought some vintage valve covers with "CHEVROLET" in a script font (factory). There's no way to install a filler caps or breathers, unless I want to ruin the covers. So I have been on a search for a spread bore (Q-Jet) manifold with the filler / vent on front that would also accomodates a circulating system thermostat fitting. I think I found one. Offenhauser Dual Plane. Using ProMAX heads my builder is machining and building up with his hardware.

    My question is how will this manifold be as a performance match to what I am trying to do? 5000-5500 rpm max.

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    (the covers)

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    Last edited by John Thompson; 01-21-2018 at 04:08 PM.

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  3. #2
    Member ezstriper's Avatar
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    those were lower RPM intakes with a strange port setup(ran one on a SB ford years ago, it should work ok for the RPM you are looking to run, but you will be giving up power VS something like performer RPM. also you are going to have to vent the engine well to run those valve covers, using the oil fill on that intake or drilling large hole in the rear, neither a great deal, those covers were used with a very early intake that had a canister in rear and what they called a road draft tube. To me the intake and valve covers better off hanging on the wall...just my .02

  4. #3
    Cpt. Millenium Falcon John Thompson's Avatar
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    Went ahead with the intake but went to vented covers. Peak HP of 356 occurs at 4800 RPM. I am happy. Calls for the AA impeller.

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