'66 Exhaust Manifold Conundrum

[Jim H.]

A couple of years ago my former mechanic made a bad decision regarding my '66 SBC non-AIR original non-sidepipe car when converting to aftermarket OEM-style sidepipes. Seems the original mainfolds were 2" diameter and the sidepipe inlet 2.5". He advised his only solution was a pair of Chinese aftermarket 2.5" exhaust manifolds. I saved the original manifolds. I want to fix this by reintalling the original manifolds and mating them to my sidepipes. NCRS manual says all non-AIR 327s got 3846559 (LH) and 3747042 (RH) manifolds. Side pipe discussion contains no mention of step down pipe or coupler. What is the correct solution (understanding that the pipes themselves are not correct)?

[Joe L.]

Re: '66 Exhaust Manifold Conundrum

A couple of years ago my former mechanic made a bad decision regarding my '66 SBC non-AIR original non-sidepipe car when converting to aftermarket OEM-style sidepipes. Seems the original mainfolds were 2" diameter and the sidepipe inlet 2.5". He advised his only solution was a pair of Chinese aftermarket 2.5" exhaust manifolds. I saved the original manifolds. I want to fix this by reintalling the original manifolds and mating them to my sidepipes. NCRS manual says all non-AIR 327s got 3846559 (LH) and 3747042 (RH) manifolds. Side pipe discussion contains no mention of step down pipe or coupler. What is the correct solution (understanding that the pipes themselves are not correct)?

James------


It does not matter what the configuration was like of the original side-pipes because you don't have those. I can tell you this: the manifold flange section of the original side pipes was configured to mate to the 2" manifold flange. There was no separate "adapter" or "reducer"

In your case, the only solution I see is to reconfigure the ends of the side-pipes at the manifold to match the manifold flange. This will involve the fabrication of some sort of reducing section.

My advice: junk the side pipes and go back to undercar exhaust.

[Jim H.]

Re: '66 Exhaust Manifold Conundrum

Thanks, Joe. I may just do that. Appreciate the advice.

[John F.]

Re: '66 Exhaust Manifold Conundrum

This is a slightly different issue but it applies to 66 exhaust manifolds so I thought I would post here. Has anyone seen this anomoly of a # missing from the casting 38808 8? It's a Sept 1966 manifold.

[Jack H.]

Re: '66 Exhaust Manifold Conundrum

Can't speak specifically to '66 exhaust manifolds, but I've seen such (missing or 'oblitherated' casting emboss digit) SEVERAL times on various water pump housings. I chaulk it up to the specific 'fill' characteristics on the mold when that particular piece was cast...

[Larry M.]

Re: '66 Exhaust Manifold Conundrum

A couple of years ago my former mechanic made a bad decision regarding my '66 SBC non-AIR original non-sidepipe car when converting to aftermarket OEM-style sidepipes. Seems the original mainfolds were 2" diameter and the sidepipe inlet 2.5". He advised his only solution was a pair of Chinese aftermarket 2.5" exhaust manifolds. I saved the original manifolds. I want to fix this by reintalling the original manifolds and mating them to my sidepipes. NCRS manual says all non-AIR 327s got 3846559 (LH) and 3747042 (RH) manifolds. Side pipe discussion contains no mention of step down pipe or coupler. What is the correct solution (understanding that the pipes themselves are not correct)?

James:

You could find and use GM 1965 exhaust manifolds which are 2-1/2 inch outlets OR use your original 2 inch outlet exhaust manifolds and get sidepipes that designed for them. GM produced two sets of sidepipes for SB cars......one set for the earlier cars with the 2-1/2 outlet and one set for the later cars with the 2 inch outlet. I have the latter ones on my 1967 SB car.

You could also have a (good) muffler shop modify the sidepipes you have to fit your original manifolds.

Larry

[Jim H.]

Re: '66 Exhaust Manifold Conundrum

Larry, Thank you for your response. I have noticed the '65 manifolds and will research them. Also the 2.5/2.0" variation in aftermarket side pipes. I'd prefer not to modify the side pipes, although that would permit use of my original manifolds. I could sell the 2.5" pipe and get the right 2.0" pipe. In any event, you've given me options. Thanks again.