1969 L46 A.I.R. Question

[Thomas C.]

I'm trying to assemble all the parts to put the A.I.R. system back on my car. I'll have other questions I'm sure, but the manifolds appear to have 3 1/8" flared tubes that I'm guessing pass air from the smog tube to the valve. If I'm incorrect in my assumption, please correct me. Is there a part number for those little tubes?

Tom

[Gary B.]

Re: 1969 L46 A.I.R. Question

Group 3.675, #3880887 Pipe, exh. gas combustion, 8-required, on 7-71 they were $0.40 each.
Gb

[Thomas C.]

Re: 1969 L46 A.I.R. Question

Thanks for the reply. That 3880887 number doesn't pull up anything on the web, even searching under images. Are they just pieces of flared brake line tubing? I have $3.60 ready to spend for a total of 8 of them.

Tom

[Gary B.]

Re: 1969 L46 A.I.R. Question

I don't think they are a carbon steel, as we know it. They are non-magnetic.

I installed a set of eight a few days ago, and they are harder than.... the dickens. A new hack saw blade just skated across the surface. One end was buggered up, so i needed to cut about 1/8" off. Terry and I think they are inconel. But, I don't know for sure.

I have made a set out of brake line tubing, and have had no ill effects so far.

I think finding a NOS or used set of those are slim to none. Kind of like finding a set of chicken lips.

Gary B

[Terry M.]

Re: 1969 L46 A.I.R. Question

I don't think they are a carbon steel, as we know it. They are non-magnetic.

I installed a set of eight a few days ago, and they are harder than.... the dickens. A new hack saw blade just skated across the surface. One end was buggered up, so i needed to cut about 1/8" off. Terry and I think they are inconel. But, I don't know for sure.

I have made a set out of brake line tubing, and have had no ill effects so far.

I think finding a NOS or used set of those are slim to none. Kind of like finding a set of chicken lips.

Gary B

In another lifetime I worked at a metals research lab affiliated with IIT (Illinois Institute of Technology). The reason I think those tubes are inconel is they stick into the exhaust gas stream and the pump puts oxygen into that gas stream to ignite and burn unburnt fuel byproducts. It is a bit like making a blow torch under some conditions. My hunch is any other less robust material will not last long. On the other hand if the car is just used on and off a trailer .... well YMMV.

If you disable the AIR pump (removing the carbon vanes inside the pump is one way) you may not need those tubes, and if you are not subject to a tailpipe emissions check you may not need them either. I should add that cleaver judges can tell if these tubes are installed in the exhaust manifolds, but IMO doing so is over the top so I will not reveal how that is discerned.

From Google:
Inconel is a registered trademark of Special Metals Corporation for a family of austenitic nickel-chromium-based superalloys. Inconel alloys are oxidation-corrosion-resistant materials well suited for service in extreme environments subjected to pressure and heat.

[James G.]

Re: 1969 L46 A.I.R. Question

IIRC Inconel is also used for the J56 pad backing plates with the bent lip at the top... again non magnetic and doesn't transfer heat anywhere near as well as carbon steel - along with the insulators on the pucks it all kept a lot of heat out of the fluid.

[Thomas C.]

Re: 1969 L46 A.I.R. Question

From what I can gather, they're currently called Smog Injector Pipe Extension Tubes or Smog Tube Extensions or Air Injection Smog Extension Tubes. I only put this for anyone searching in the future. They vary wildly in price from vendors, but I expect that is because of the quality of material used.

The "original" ones that were in the manifold that I purchased were slightly magnetic (my used manifold came with 3). They will attach to a strong magnetic, but not very well. So they must be made of something other than steel. First I've heard of Inconel, but sounds plausible.

Do the tubes install from the outside of the manifold before the AIR Injection pipes screw into the manifold? Also, are there any copper gaskets or anything that goes into the holes in the manifold or does the threaded nipple/nut on the AIR injection pipe tighten up against the extension tubes creating a seal?

Final question (maybe)....where should I look to pickup a set of those injection pipes? I'm not building a show-quality car, but I'd like it to look/perform as original. Thanks for everyone's help.

Tom

[Terry M.]

Re: 1969 L46 A.I.R. Question

Do the tubes install from the outside of the manifold before the AIR Injection pipes screw into the manifold? Also, are there any copper gaskets or anything that goes into the holes in the manifold or does the threaded nipple/nut on the AIR injection pipe tighten up against the extension tubes creating a seal?

Final question (maybe)....where should I look to pickup a set of those injection pipes? I'm not building a show-quality car, but I'd like it to look/perform as original. Thanks for everyone's help.

Tom

Yes, Tom, the tubes install from the outside of the manifold and are held in place by the AIR Injection pipes. The threaded nipple/nut on the AIR injection pipe tightens up against the extension tubes creating a seal. No washer or anything else is used. It would be prudent to be sure the tubes fit in place before securing the manifold to the head.

Many exhaust manifolds have been treated to pipe plugs when the AIR tubing is removed. That can damage the threads in the exhaust manifold since those threads are straight and the pipe plug is tapered. This damage could keep the AIR pipes from securing the tubing into place. Again, it would be prudent to check all these fits before the manifold is installed to the head.

I was able to secure a used set of the Inconel tubes from evilBay for what I consider a reasonable price. I actually came across them while looking for another part. Some were a little shorter than others, but no one will be able to judge them so I was not concerned.

[Joe L.]

Re: 1969 L46 A.I.R. Question

In another lifetime I worked at a metals research lab affiliated with IIT (Illinois Institute of Technology). The reason I think those tubes are inconel is they stick into the exhaust gas stream and the pump puts oxygen into that gas stream to ignite and burn unburnt fuel byproducts. It is a bit like making a blow torch under some conditions. My hunch is any other less robust material will not last long. On the other hand if the car is just used on and off a trailer .... well YMMV.

If you disable the AIR pump (removing the carbon vanes inside the pump is one way) you may not need those tubes, and if you are not subject to a tailpipe emissions check you may not need them either. I should add that cleaver judges can tell if these tubes are installed in the exhaust manifolds, but IMO doing so is over the top so I will not reveal how that is discerned.

From Google:
Inconel is a registered trademark of Special Metals Corporation for a family of austenitic nickel-chromium-based superalloys. Inconel alloys are oxidation-corrosion-resistant materials well suited for service in extreme environments subjected to pressure and heat.

Terry------


I don't think the tubes are Inconel, per se, but they are a very high nickel alloy steel.

The shorter tubes were big block tubes, GM #3882805. Those were discontinued in 1993 and replaced by the small block 3877484. The latter were discontinued about 20 years ago.

Tubes GM #14007363 or 12338013, which were used on later C3, can be used. These have a different outlet configuration but will work fine. However, they are both GM discontinued and may also be difficult to find.

I believe that reproductions are available but I don't know if they are made of the proper alloy.

I would NEVER use ordinary steel tubing to make these up.