74' Drivers Side Exhaust Manifold P/N Help

[Robert S.]

My 74' L48 4 Speed has a P/N 3872766 exhaust manifold installed on the drivers side rather than the 3932461 or 3989036 called out in the judging guide. The passenger side manifold is the correct P/N as are all of the other major engine pieces.
Can someone tell me if my P/N 3872766 manifold is possibly a factory installed part?

[Joe L.]

Re: 74' Drivers Side Exhaust Manifold P/N Help

My 74' L48 4 Speed has a P/N 3872766 exhaust manifold installed on the drivers side rather than the 3932461 or 3989036 called out in the judging guide. The passenger side manifold is the correct P/N as are all of the other major engine pieces.
Can someone tell me if my P/N 3872766 manifold is possibly a factory installed part?

Robert------


There was no exhaust manifold of GM casting #3872766 that I am aware of. However, there was a manifold of GM casting number 3872765 and that may be what you have (a "5" and a "6" can be difficult to distinguish between on casting numbers).

If it is a GM #3872765 it will have an integral forward bracket for alternator mounting and it will have AIR fittings. The 3872765 was used extensively on small block Corvettes in the 1966-71 period, but it was not used after 1971. After 1971, the integral alternator mount was eliminated from the left side manifold and, instead, a bracket which bolted to the forward end of the left side cylinder head was used for alternator mounting.

[Robert S.]

Re: 74' Drivers Side Exhaust Manifold P/N Help

Joe - Thank you for the quick reply - I must have misread the part number as the part is as you describe it - the manifold has an integral mount for the P.S. pump and has air fittings.

[Joe L.]

Re: 74' Drivers Side Exhaust Manifold P/N Help

Joe - Thank you for the quick reply - I must have misread the part number as the part is as you describe it - the manifold has an integral mount for the P.S. pump and has air fittings.

Robert------


The mount is not for the power steering pump. It's used for the alternator mounting. Does your car have the alternator mounted to this or is it unused and a separate bracket mounted to the cylinder head is used for alternator mounting?

I suspect that someone replaced the original manifold with this one. It would work as long as the integral bracket did not interfere with the original style alternator mounting.

[Robert S.]

Re: 74' Drivers Side Exhaust Manifold P/N Help

I was replying from memory which is always dangerous. You are correct, the manifold mounts the alternator. There is no evidence of a separate bracket on the front of the block. The manifold, as installed, works fine in all respects and looks like a factory installation.

[Joe L.]

Re: 74' Drivers Side Exhaust Manifold P/N Help

I was replying from memory which is always dangerous. You are correct, the manifold mounts the alternator. There is no evidence of a separate bracket on the front of the block. The manifold, as installed, works fine in all respects and looks like a factory installation.

Robert------


Yes, it should work just fine to mount the alternator. However, this manifold should not have been used for 1974. The last use of it was for 1971. So, I'd guess that someone replaced the original manifold somewhere along the way with this one. When they did this they removed the bracket mounted to the cylinder head (probably because it interfered) and used the manifold to mount the alternator, just as was done for 66-71 Corvettes.

From a FUNCTIONAL perspective, it should work perfectly. However, it would not be considered a correct configuration by NCRS or NCCB.

Is it possible that the factory built it this way? I'd say it is REMOTELY, and I mean REMOTELY, possible. However, even if it was, it would not be considered "typical of factory production" for the 1974 model year and you'd need substantial documentation to get anyone to believe that it was originally built that way.

By the way, the 3872765 has a cast-in date, usually on the rear side of the manifold. However, even if the date was late 1973 or 1974, that would not necessarily mean the manifold was original to the car since this manifold was still being manufactured for SERVICE in 1974 and long after. If the manifold had a date that was after the engine build date, though, then it could not have been original to the car.