Another Potential Error in the 1966 Judging Guide

[John L.]

The latest edition of the manual states that the 1966 L-79 327/350 should have 2 1/2 inch side exhaust pipes. I believe that is incorrect due to the following information.

The Exhaust manifold used on 1966 L-79 327/350 w/o K-19 per the NCRS Corvette Specifications Guide was Part No 3846559 for the LH and 3747042 for the RH. The 1966 JG states the same. Using as a reference "Chevrolet by the Numbers" by Alvin Coleman is the following. For RH manifold the Outlet size is 1.96" which equates to 2". For the LH manifold the outlet size is 2.026" which also equates to 2". Both of these manifolds were also used on the 1965 Corvette 250 & 300 HP which if memory serves me correctly used the 2" side exhaust.

Furthermore, the NCRS Corvette Spec Guide states that the 1965 327/350 HP car w/o A/C used Exhaust Manifolds 3846563 for the LH and 3797902 for the RH. Again using Colvins book it states that the LH 3846563 manifold had a 2.526" outlet which equates to 2 1/2". Likewise the RH 3797902 manifold also had a 2.526 outlet which also equates to 2 1/2".

Based on this information I feel that the 1966 JG is in fact incorrect and should call for a 2" side pipe for the 1966 L-79 327/350 w/o K-19. Just from a reasonable test one would have to wonder how you would mount a 2 1/2 inch sidepipe to a manifold designed for 2". Now if you tell me the sidepipe changes size at some point where it flares from 2" to 2 1/2 inch, that would be a reasonable explanation. However I dont believe it does. Also I don't think the exhaust extensions that support the donut insulator and go between the exhaust manifold and the sidepipe would ever fit.

Additionally if you check the Long Island Corvette Supply, Chicago Corvette Supply and Paragon Corvette Supply catalogs, they call for a 2" side exhaust for the 66 327/350. The 65 327/350 calls for a 2 1/2 " but not 66.

Your comments on this are greatly appreciated.

regards

john lolli

[William C.]

Re: Another Potential Error in the 1966 Judging Gu

The pipes are reduced in size a short didtance from the manifold to adjust fron the 2 1/2 inch pipe to the 2 inch manifold. This is one of the unique features of the '66-67 SHP exhaust systems that are difficult to replicate

[Joe L.]

Re: Another Potential Error in the 1966 Judging Gu

Bill and John------

Yes, I agree. From 1966-onward, no Corvette small block used anything other than 2" outlet exhaust manifolds. However, the actual exhaust systems for SHP small blocks and, even, a few others (like base engine 1968 Corvettes) were 2-1/2". This included BOTH undercar exhaust as well as side-exhaust-equipped cars.

As Bill mentioned, the 2-1/2" forward exhaust pipe was swaged down near the manifold to provide for the 2" connection. Why did Chevrolet abandon the 2-1/2" outlet small block exhaust manifolds after 1965? I don't know for sure, but I expect that it had something to do with the fact that air injection reaction systems first came on-line for some 1966 models. I don't think that GM wanted to (or, for some reason, couldn't) re-tool the 2-1/2" outlet manifolds for AIR. And, they probably didn't want to use the 2" outlet manifolds for AIR and the 2-1/2" outlet for non-AIR. So, the 2-1/2" outlet manifolds "passed into history".

You can still purchase them in SERVICE, though, and add them to most non-AIR-equipped small blocks.

[John L.]

Re: Another Potential Error in the 1966 Judging Gu

Is there someone out there that can email me or post pictures of an original sidepipe exhaust for a 1966 or 1967 327/350. The pictures I need are where the pipe goes from 2" to 2 1/2". I think this occurs approximately 3" before the pipe reaches the front sidepipe cover bracket.

thank you very much

john lolli

[John L.]

Where does the s/p flare from 2" to 2 1/2"

Could someone please explain where an original sidepipe on a 66 327/350 flares from 2" to 2 1/2". I thought it was approximately 3" before it reaches the front mounting bracket.

thanks

john lolli

[John H.]

Re: Where does the s/p flare from 2" to 2 1/2"

John -

I have a picture of this somewhere, but I can't locate it at the moment - as I recall, the pipe swage point was 4"-5" or so below the manifold flange.