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  1. #1
    Join Date
    Aug 2014
    Holley, New York

    Default 66 standard exhaust manifolds

    I have the original log manifolds on my '66 GTO 389, they are showing their age. I recently came across what look to be a really good clean set that is being advertised as being removed from a '68 GTO. I know Pontiac used the same manifolds with the same part numbers from 65 to 68, without date codes. My left manifold has the part number 9779032-2, the "new" set has 9779032-1. This is the only difference I can find on this one. My right manifold is where I'm seeing a noticeable difference. My manifold 9779328 GM 4, the new one same part #, GM 3. My manifold was cast with lugs on the exhaust ports centered between the bolt holes where they mount to the head, I'm guessing for added strength. The "new" manifold is smooth. Is the difference in castings just because they came off of a different casting machine, or a revised design from 66 to 68? My big question is if I buy these manifolds to use, when it comes to judging at POCI or GTOAA, would they be correct, or would it be noticeable they came off a different car? After owning the car for 20 years, I have now become anal about making sure the car is as it was when it left the factory, save for a couple of bolt on options that I have added. Thanks for any help. Scott

  2. Default

    The 1965-1968 Tempest/LeMans/GTO LH exhaust manifold s/b 9779032. I don't know what the -1 or -2 represents, possibly night or day shift casting, it's ignored.

    Here are the numbers from the MPC.

    These are part numbers which may or may not be same as casting number. They are usually close but not always the same. The -2 and -1 on the left are a bit of a mystery. The GM3 vs GM4 has always been a mystery to me. Same year, same part may have d

    The 1965-1968 Tempest/LeMans/GTO RH exhaust manifold s/b 9779325. I don't find a 9779328, I suspect the numbers are being mis-read. The GM 4 is a newer revision than the GM 3 and I believe the cast lugs on the newer version are there to be drilled and tapped for the addition of the A.I.R. (Air Injection Reactor) or "California Smog" lines where a belt driven air pump injected air into the exhaust to cut down on emissions.

    I'm not sure of and cannot find the exact date that GM made the revision to add the lugs, but the California smog option started on 1966 Pontiacs. I believe for 1966 production, they phased in adding the lugs to all exhaust castings to avoid producing and stocking 2 versions (smog or non-smog) .

    For judging at POCI, I would expect to see the lugs on the exhaust manifolds of a 1966 GTO, but "lug-less" manifolds would have been used until the supply was "exhausted" * happy. If the 2 letter engine code indicates a CAL smog engine, I would expect to see the entire smog system in place and functional.

    I may be proven wrong, but I seriously doubt that a "smooth" 9779325 GM3 manifold came off of a 1968 GTO from the factory, probably from a 1965 and transplanted into the '68.

    Rick Gonser
    Paul Bergstrom
    POCI Club Office Mgr.

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