68-69 Judging Guide-manifold #'s ??

[Steve G.]

My '68-'69 Judging Guide says the correct exhaust manifolds are 3872765 or 3932461 (LH) and 3932481 (RH).

Then it notes that late '69s have had '70 manifolds: 3846559 or 396986 (LH) or 3932461 (RH)... but this is one of the numbers for LH in 1969. Is this right?

[Joe L.]

Re: 68-69 Judging Guide-manifold #'s ??

Steve-----

I think that this is an area that we're going to need to make changes in future editions of the JG. Quite frankly, I'm surprised that we didn't catch it in the review of the JG (the "we" includes me).

1968-69 Corvettes with small block used manifold GM #3872765 for the left (driver) side. Period. This is the only manifold that GM ever manufactured with the configuration necessary for all 1968-69 Corvette small block left side manifolds. Those features are (1) rams horn design, (2) straight outlet with 2" flange, (3) provisions for AIR, and (4) cast-in bracket on the forward end for alternator mounting. No other manifold ever manufactured by GM had all of these features. Therefore, no other manifold could have been used for the left side for 1968-69 small blocks.

The GM #3932461 manifold is similar to the 3872765 EXCEPT it does not have provisions for the generator mounting bracket. So, it could not have been used for the left side. It was, however, used for the right side for 1968-69. There never was a manifold of GM #3932481. I believe that's someone's mis-interpretation of the next to last digit (i.e. the "3", "6", "8", and "9" casting number syndrome).

The 3932461 is virtually identical to the GM #3872778. In fact, the 3872778 MAY have been used for some 1968 Corvette small blocks, right side. I don't think it was used for 1969, though. However, there was no functional reason that it could not have been used. The GM #3932461 and 3872778 were the ONLY manifolds that GM was manufacturing at the time that could have been used for the 1968-69 small block, right side application.

I have no information, whatsoever, on a manifold of GM #396986. If it existed, at all, I don't think it was ever originally used on a Corvette. Certainly, it would not have been used as early as 1968-69.

NO 1968-1969 Corvette could possibly have used manifold GM #3846559. That's because this manifold does not have provisions for AIR. Since ALL 1968-69 Corvettes had AIR, its use would have been completely incompatible. Period. 1970-71 Corvette small blocks with base engine or L-46 (1970) did use manifold 3846559. Those engines did not use AIR and the 3846559 was otherwise configured properly for that application (i.e. it had rams horn design, 2" outlet, and forward, cast-in alternator bracket).

One other point: just in case any of you "eagle-eyed" parts fanatics have thought of this, it is THEORETICALLY possible that manifold GM #3932461 (or, GM #3872778) could have been used for the left side for 1969 small blocks IF used IN CONJUNCTION WITH alternator bracket GM #3951337. That bracket was in the "parts bin" and available for the 1969 model year. It was used for 1969 Chevrolet light trucks with small block. However, it was not used on a Corvette until the 1972 model year. It may have "found its way onto" 1969-71 Corvette small blocks, though, if someone needed a left side manifold, couldn't find the right one, substituted an easier-to-find GM #3932461 (or, other non bracketed manifold) and used the GM #3951337 to mount the alternator. That could have very easily happened, but I really don't think that it ever happened at St. Louis during 1969-71.

[Joe L.]

Re: 68-69 Judging Guide-manifold #'s ??

Steve-----

I think that this is an area that we're going to need to make changes in future editions of the JG. Quite frankly, I'm surprised that we didn't catch it in the review of the JG (the "we" includes me).

1968-69 Corvettes with small block used manifold GM #3872765 for the left (driver) side. Period. This is the only manifold that GM ever manufactured with the configuration necessary for all 1968-69 Corvette small block left side manifolds. Those features are (1) rams horn design, (2) straight outlet with 2" flange, (3) provisions for AIR, and (4) cast-in bracket on the forward end for alternator mounting. No other manifold ever manufactured by GM had all of these features. Therefore, no other manifold could have been used for the left side for 1968-69 small blocks.

The GM #3932461 manifold is similar to the 3872765 EXCEPT it does not have provisions for the generator mounting bracket. So, it could not have been used for the left side. It was, however, used for the right side for 1968-69. There never was a manifold of GM #3932481. I believe that's someone's mis-interpretation of the next to last digit (i.e. the "3", "6", "8", and "9" casting number syndrome).

The 3932461 is virtually identical to the GM #3872778. In fact, the 3872778 MAY have been used for some 1968 Corvette small blocks, right side. I don't think it was used for 1969, though. However, there was no functional reason that it could not have been used. The GM #3932461 and 3872778 were the ONLY manifolds that GM was manufacturing at the time that could have been used for the 1968-69 small block, right side application.

I have no information, whatsoever, on a manifold of GM #396986. If it existed, at all, I don't think it was ever originally used on a Corvette. Certainly, it would not have been used as early as 1968-69.

NO 1968-1969 Corvette could possibly have used manifold GM #3846559. That's because this manifold does not have provisions for AIR. Since ALL 1968-69 Corvettes had AIR, its use would have been completely incompatible. Period. 1970-71 Corvette small blocks with base engine or L-46 (1970) did use manifold 3846559. Those engines did not use AIR and the 3846559 was otherwise configured properly for that application (i.e. it had rams horn design, 2" outlet, and forward, cast-in alternator bracket).

One other point: just in case any of you "eagle-eyed" parts fanatics have thought of this, it is THEORETICALLY possible that manifold GM #3932461 (or, GM #3872778) could have been used for the left side for 1969 small blocks IF used IN CONJUNCTION WITH alternator bracket GM #3951337. That bracket was in the "parts bin" and available for the 1969 model year. It was used for 1969 Chevrolet light trucks with small block. However, it was not used on a Corvette until the 1972 model year. It may have "found its way onto" 1969-71 Corvette small blocks, though, if someone needed a left side manifold, couldn't find the right one, substituted an easier-to-find GM #3932461 (or, other non bracketed manifold) and used the GM #3951337 to mount the alternator. That could have very easily happened, but I really don't think that it ever happened at St. Louis during 1969-71.

[Steve G.]

Re: 68-69 Judging Guide-manifold #'s ??

Great answer Joe. Super helpful.

After I posted this, I looked at the exhaust manifold list in the back of Dobbins' book on 68-72. I see that #765 is listed for the LH, while the #481 is listed for the RH for all small-blocks in 1969. The #461 is not listed in Dobbins' page until the 1970, RH, 370hp. And, the #778 is listed for the 1968, RH small blocks only.

Lots of conflicting info out there. I agree the JG needs a "tweak."

[Steve G.]

Re: 68-69 Judging Guide-manifold #'s ??

Great answer Joe. Super helpful.

After I posted this, I looked at the exhaust manifold list in the back of Dobbins' book on 68-72. I see that #765 is listed for the LH, while the #481 is listed for the RH for all small-blocks in 1969. The #461 is not listed in Dobbins' page until the 1970, RH, 370hp. And, the #778 is listed for the 1968, RH small blocks only.

Lots of conflicting info out there. I agree the JG needs a "tweak."

[Dick W.]

Re: 68-69 Judging Guide-manifold #'s ??

'69 Manual contains a typo on the RH # It should read 3989036 instead of 369986. It is duly noted for the next revision whenever.

[Dick W.]

Re: 68-69 Judging Guide-manifold #'s ??

'69 Manual contains a typo on the RH # It should read 3989036 instead of 369986. It is duly noted for the next revision whenever.

[Jim B.]

Re: 68-69 Judging Guide-manifold #'s ??

This explains why I have had so much trouble replacing my very corroded RH exhaust manifold. The NCRS Corvette Specification Guide calls for a 3872778 right hand manifold for ALL 68 Corvette small blocks. My original right hand manifold (wouldn't you know it) is long gone due to the Salt treated roads of the Northeast. Strangely enough I still have the Original Left hand manifold and it matches the number in the Spec Guide 3872765. (Or as close as I can read it) It also is not in the best of shape. Paragon makes a very good new casting that has this number. It is identical to my original Left hand Manifold. I have not been able to find a right hand manifold in great shape. I found an older one that someone had blasted and restored at Kissemee in January but too much money for the condition.

The spec guide calls for a 3932461 for a 69 right hand manifold. Since I have a very late (July 1968) build could thid one have been used on my car?? I am still confused.

[Jim B.]

Re: 68-69 Judging Guide-manifold #'s ??

This explains why I have had so much trouble replacing my very corroded RH exhaust manifold. The NCRS Corvette Specification Guide calls for a 3872778 right hand manifold for ALL 68 Corvette small blocks. My original right hand manifold (wouldn't you know it) is long gone due to the Salt treated roads of the Northeast. Strangely enough I still have the Original Left hand manifold and it matches the number in the Spec Guide 3872765. (Or as close as I can read it) It also is not in the best of shape. Paragon makes a very good new casting that has this number. It is identical to my original Left hand Manifold. I have not been able to find a right hand manifold in great shape. I found an older one that someone had blasted and restored at Kissemee in January but too much money for the condition.

The spec guide calls for a 3932461 for a 69 right hand manifold. Since I have a very late (July 1968) build could thid one have been used on my car?? I am still confused.

[Joe L.]

Re: 68-69 Judging Guide-manifold #'s ??

Dick-----

The GM #3989036 could not have been used on any 1968 or 1969 Corvette. It may have been used for 1970, although I would expect its use to be later-build cars. It didn't even exist in 1968-69, though. Also, I don't think that the 3989036 was equipped with AIR fittings, so that's another reason it would not have been used for 1968-69. It's possible, though, that some 3989036 did have AIR fittings, but, as I say, even if they did, I don't think that any would have been used for 1968-69.

[Joe L.]

Re: 68-69 Judging Guide-manifold #'s ??

Dick-----

The GM #3989036 could not have been used on any 1968 or 1969 Corvette. It may have been used for 1970, although I would expect its use to be later-build cars. It didn't even exist in 1968-69, though. Also, I don't think that the 3989036 was equipped with AIR fittings, so that's another reason it would not have been used for 1968-69. It's possible, though, that some 3989036 did have AIR fittings, but, as I say, even if they did, I don't think that any would have been used for 1968-69.

[Joe L.]

Re: 68-69 Judging Guide-manifold #'s ??

Jim-----

I really think that the GM #3932461 was used for most, if not all, 1968 Corvette small blocks. What I said earlier is that it's POSSIBLE that the 3872778 was used for 1968 right side. IF it was, I expect that by late model year the 3932461 was being used. The 3932461 implies a 1968-issued part number. Why release a part if it's not going to be used?

One of the reasons that I expect the 3872778 is so hard to find is that it was primarily used for 1966-67 passenger and Corvette small blocks with AIR. That means pretty much California cars only.

I'd be very interested to know if anyone has a GM #3872778 with a casting date that would work for a 1968 Corvette.

[Joe L.]

Re: 68-69 Judging Guide-manifold #'s ??

Jim-----

I really think that the GM #3932461 was used for most, if not all, 1968 Corvette small blocks. What I said earlier is that it's POSSIBLE that the 3872778 was used for 1968 right side. IF it was, I expect that by late model year the 3932461 was being used. The 3932461 implies a 1968-issued part number. Why release a part if it's not going to be used?

One of the reasons that I expect the 3872778 is so hard to find is that it was primarily used for 1966-67 passenger and Corvette small blocks with AIR. That means pretty much California cars only.

I'd be very interested to know if anyone has a GM #3872778 with a casting date that would work for a 1968 Corvette.

[Joe L.]

Addendum

Dick-----

If anyone out there has a GM #3989036 that does have AIR fittings, I'd be very interested in learning about that,

[Joe L.]

Addendum

Dick-----

If anyone out there has a GM #3989036 that does have AIR fittings, I'd be very interested in learning about that,