62 FI "real" r/h exhaust manifold

[E S.]

I'm sure this has been discussed before, but how do you decide if a 3797902 R/H is "real" (as came from factory on a car)? or a re-pro. or re-issue?

[Keith R.]

Re: 62 FI "real" r/h exhaust manifold

I don't know if this applies to a '62 but a '60 FI manifold is GM Part #3750556. A "real" one has no heater riser tube or evidence that there was one at any time. According to the TIMJ, there are eight "burrs" along the top mold parting line where the gate was broken off the casting. There are no grind marks on original manifolds. Tonawanda manifolds do not have burrs. Replacement manifolds may have two to five burrs that are typically larger and more pronounced or may be completely ground off. There are two small bosses on top, one near each end. One boss is slightly rectangular about 1/2" X 11/16". The other is nearly square, about 1/2" X 5/8". Later replacements have noticeably larger bosses.

You should probably get your hands on a 61-62 TIMJ and see what it says

[E S.]

Re: 62 FI "real" r/h exhaust manifold

Keith- Thanks for the info- What you described sounds exactly what I have, even though mine are 901 and 902-(I did not know there are Tonawanda manifolds)
Seems like there so many variations of the 901 and 902's even though one supplier claims to have the original GM molds.
Thanks again for the reply
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[Michael G.]

Re: 62 FI "real" r/h exhaust manifold

I don’t know that the ‘62 L.H. manifold looks like that, it doesn’t for ‘63-5. As for the R.H. one, it is the correct shape, but its hard to tell if the choke tube hole has been welded up without removing that paint from the manifold. The top surface where the hole is normally found looks a bit odd, sort of concave, which I haven’t seen before. Maybe that’s just the pics. You may want to take a scope and look inside at that depression (where the hole would be found) to see if there’s evidence of the hole having been filled. You’ll lose points with that paint, but the weld may show up without it...

[E S.]

Re: 62 FI "real" r/h exhaust manifold

Mike- Yes -62 FI uses a 3797901 on the L/H side, where 63-65 FI uses 3797942 on the LH side (because of the FI air cleaner can)
By the way- These manifolds are not painted- They were bead blasted.

[Michael G.]

[Tom P.]

Re: 62 FI "real" r/h exhaust manifold

Mike,
Up through 63, left manifolds had the gen/alt mounting holes facing the LEFT side, regardless of 2" or 2 1/2" versions (63-5 FI engines used the 942 with NO alt mounting bracket). ALL 942 manifolds that I've ever seen have a heat riser tube for the choke (left side for FI, right side for carb).
Then beginning in 64, the manifold alt mounting holes faced FORWARD on the left manifolds (3846563), second picture.

The first picture is a GM 62-3 3797901 left manifold, compared to a Chinese replacement (NOT repo) imported by Dorman and available at most parts stores, or online vendors.

[Tom P.]

Re: 62 FI "real" r/h exhaust manifold

As far as I know, ALL 2 1/2" RIGHT side manifolds were the same with an alt bracket with 2 holes facing the RIGHT side.
Air cond cars got a 942 on the right side with PLAIN ends (NO alt mounting bracket).
As I mentioned, as far as I know, ALL 942 manifolds had the heat riser tube for a choke.
The 942 is the hardest to come by because it was not as commonly used as the 901/902/563 manifolds. Nor was it available as a service replacement. Only 901/902/563 manifolds were available as service replacements for many years.
BUT, in desperation, with care, patience, skill, a 563 CAN BE modified to duplicate the plain end of a 942 manifold. Then, if needed, holes can be drilled to insert a heat tube. I've done this to several 563 manifolds. I actually have one on the FI SB400 in my 56 (without the heat tube).

[Michael G.]

Re: 62 FI "real" r/h exhaust manifold

Tom, the manifold that I was writing about (shown in the first pic of post #3) is a 3797902, with no drilled choke hole. It was used on the passenger side of all mid-year fuelies, as the choke tube on those cars is on the driver’s side. It has provisions for passenger-side alternator mounting of the C2 fuelies. It is extremely rare, I haven’t seen one offered for sale in 15 years - and I’ve scoured flee markets for at least that long. If the one shown in the OP’s pic is real (not welded) its pretty valuable...I’d buy it, if E J wants to part with it...

I’ve never owned a C1 and am not familiar with ‘62 usage of this manifold. Perhaps you can edumacate me

[Tom P.]

Re: 62 FI "real" r/h exhaust manifold

Tom, the manifold that I was writing about (shown in the first pic of post #3) is a 3797902, with no drilled choke hole. It was used on the passenger side of all mid-year fuelies, as the choke tube on those cars is on the driver’s side. It has provisions for passenger-side alternator mounting of the C2 fuelies. It is extremely rare, I haven’t seen one offered for sale in 15 years - and I’ve scoured flee markets for at least that long. If the one shown in the OP’s pic is real (not welded) its pretty valuable...I’d buy it, if E J wants to part with it...

I’ve never owned a C1 and am not familiar with ‘62 usage of this manifold. Perhaps you can edumacate me

To the best of my knowledge, ALLLLLLLLLLLLL carbs---------------up to 65 (66-later went to divorced choke), had the heat riser tube ONLY on the right side (I have ZERO knowledge of a carb with a left side choke using heat from the left manifold). Thus, ANY right side manifold on a car with a carb, got the heat riser tube in the manifold.
The 901 and 563 were ONLY left side manifolds.
The 902 was ONLY a right side manifold.
BUUUUUUUUUUT, the 942 could be EITHER a left (FI engines) or a right side (carb engine with air cond) manifold. If a 942 was used on the right side, it had the heat tube for the choke on a carb. If it was used on the left side, it had the tube for the FI choke.
For 62 models, ALL engines (regardless of engine option/2" or 2 1/2" manifolds), BOTH manifolds were cast with a generator bracket . In 58, the generator moved over to the right side, requiring a manifold with a generator bracket. In 62, BOTH manifolds had a generator bracket, one on the right for the generator, one on the left for the over flow tank. Thus, 62 models with 2 1/2" manifolds were ONLY 901/902-----------------NO 942 manifolds for 62.
Finally, for ANY, repeat, ANY 63-65 Corvette, there was EITHER a 902 manifold with a heat tube, OR, a 942 manifold with a heat tube.
I'm not aware of a FACTORY PRODUCTION 902 manifold without a heat tube being installed on a car.
BUT, with that said, there may have been some SERVICE REPLACEMENT 902 manifolds without a heat tube.
And keep in mind, 65 was the LAST year for the 2 1/2" manifolds, AND, it was the last year for exhaust heat for the choke. As I mentioned, the divorced choke was on 66-later carbs. This all pertains to small blocks. As an addition, for BIG BLOCKS, this makes the RIGHT side ex manifold and intake manifold unique and specific to the 65 396 engine -------------- ONE YEAR ONLY (actually, only 1/2 year)!

[Mike M.]

Re: 62 FI "real" r/h exhaust manifold

tom: a 64 283 2bbl carb chevy pass car right exhaust manifold wasn't drilled for choke heat riser tube. i've got some here. however, they are 2" header pipe types/ mike

[Mike E.]

Mike,
Up through 63, left manifolds had the gen/alt mounting holes facing the LEFT side, regardless of 2" or 2 1/2" versions (63-5 FI engines used the 942 with NO alt mounting bracket). ALL 942 manifolds that I've ever seen have a heat riser tube for the choke (left side for FI, right side for carb).
Then beginning in 64, the manifold alt mounting holes faced FORWARD on the left manifolds (3846563), second picture.

The first picture is a GM 62-3 3797901 left manifold, compared to a Chinese replacement (NOT repo) imported by Dorman and available at most parts stores, or online vendors.

[Tom P.]

Re: 62 FI "real" r/h exhaust manifold

tom: a 64 283 2bbl carb chevy pass car right exhaust manifold wasn't drilled for choke heat riser tube. i've got some here. however, they are 2" header pipe types/ mike

I presume you are referring to the style used on Chevelles with a SB, right? I was actually referring to the 2 and 2 1/2 Ram Horn style used on Corvettes and full size cars.
I don't know what the Chevelles with a 2bl carb did for heat for the choke.

AND, now that you have mentioned it, are you aware of, or ever seen a 2 1/2in manifold for the 64 Chevelles??????? In Robert Colvin's 60-64 book he shows a 2 1/2" Chevelle style manifold for "presumably" a 365hp/327 in the 64 Chevelle (LOTS of debate if such was ever built). I'd give almost anything for a pair of those for my Chevelle!!!!!!!

[Michael G.]

Re: 62 FI "real" r/h exhaust manifold

Finally, for ANY, repeat, ANY 63-65 Corvette, there was EITHER a 902 manifold with a heat tube, OR, a 942 manifold with a heat tube.
I'm not aware of a FACTORY PRODUCTION 902 manifold without a heat tube being installed on a car. !

As I said, and John confirms in the quote below, factory production 63-65 fuelies used a 902 manifold without a heat tube on the passenger side.

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[Tom P.]

Re: 62 FI "real" r/h exhaust manifold

VERY GOOD, I just have not seen a 902 without the hole for the choke tube.