302 exhaust manifold re-visited

[George W.]

Hi all. I happen to have a couple sets of 301/302 exhaust manifolds, and a couple of mis-matched ones. All appear to be original, all have the "teats" or "tits", casting flashes appear as original, etc.. Here's the question: One of the odd 302's does not have the choke hole drilled. I've heard from one source that this is a GM replacement manifold, and that the choke holes were not drilled until the manifold was scheduled for assembly on the line. This seems unlikey to me. Seems like the manifolds would have been cast with the choke hole, then the tube installed? Does anyone know the foundry proceedure for these castings? On the other hand, why would any company reproduce a 302 without the choke tube? Thanks in advance, george

[Wayne M.]

Re: 302 exhaust manifold heat tube (re-visited)

Way back in the early '90s, I visited Rick Miller, of Corvette fame, in
San Diego. He had an real early '66 (3-digit VIN if I recall) that had an undrilled boss on its "302". Perhaps it was an over-the-counter item.

[John H.]

Re: 302 exhaust manifold re-visited

George -

Perhaps that same raw casting was used for other 396 applications (passenger cars, Chevelles, etc.) that didn't require the hot-air choke system, thus no hole. At any rate, the hole for the hot-air tube wasn't cast-in at the foundry; it was drilled as part of the manifold machining process at Tonawanda. If a run of manifolds didn't require the hole, the auto-feed drill was disabled in that transfer station to create a different end-item part number than the one that required the hole.

[George W.]

Re: 302 exhaust manifold re-visited

Thanks guys, the info concerinig when and how the hole was drilled is especially helpful. The Chip Miller early '66 info is very interesting. This particular 302 is cast C 31 5, which seems a bit early to have found it's way to a '66---I wonder what the cast date was on Chip's car? Anyway, this info helps confirm that this is a real GM part---now how do I find a machine shop that can drill it properly and have the tube installed---or should I leave it alone? Great board, many thanks, G.

[George W.]

Re: 302 exhaust manifold re-visited

Thanks guys, the info concerinig when and how the hole was drilled is especially helpful. The Rick Miller early '66 info is very interesting. This particular 302 is cast C 31 5, which seems a bit early to have found it's way to a '66---I wonder what the cast date was on Ricks's car? Anyway, this info helps confirm that this is a real GM part---now how do I find a machine shop that can drill it properly and have the tube installed---or should I leave it alone? Great board, many thanks, G.