Help - Stock 74 BB A.I.R. (Smog) Tube Confusion

[Victor S.]

Hi All -

Trying to figure out correct Smog tubes for my 74 BB.

74 AIM says that the left and right tube assemblies for ALL (350/454) 1974 V-8 engines are the same:
Left assembly tube part #333831 and right #333832.

However, the Corvette parts and illustration catalogue show two different part numbers for the 350 and the 454 engines – and the AIM numbers that I listed above are only for the 350 engine (according to the parts and illustration catalogue).

The parts and illustration catalogue show that Part numbers 333823 (left tube) and 333824 (right tube) are the correct ones for the 454 only.

Does anyone know which set of numbers are correct for the 74 454?

Thank you,
Vic

[Joe L.]

Re: Help - Stock 74 BB A.I.R. (Smog) Tube Confusion

Hi All -

Trying to figure out correct Smog tubes for my 74 BB.

74 AIM says that the left and right tube assemblies for ALL (350/454) 1974 V-8 engines are the same:
Left assembly tube part #333831 and right #333832.

However, the Corvette parts and illustration catalogue show two different part numbers for the 350 and the 454 engines – and the AIM numbers that I listed above are only for the 350 engine (according to the parts and illustration catalogue).

The parts and illustration catalogue show that Part numbers 333823 (left tube) and 333824 (right tube) are the correct ones for the 454 only.

Does anyone know which set of numbers are correct for the 74 454?

Thank you,
Vic

Vic------


The AIR tubes ("trees") for 1974 LS-4 were GM #333823, left side, and 333824, right side. Original tubes had a "black phosphate-like" finish. Some later SERVICE tubes may have had a zinc plated with chromate overplate finish.

[Victor S.]

Re: Help - Stock 74 BB A.I.R. (Smog) Tube Confusion

THANKS SO MUCH, JOE! You saved us again...

[Robert R.]

Re: Help - Stock 74 BB A.I.R. (Smog) Tube Confusion

Vic,

I happen to own 2 '74 Corvettes. I am the original owner of my L-48 Coupe and the second owner since 1993 of an original 19,000 mile big block convertible. I just looked at both cars and will verify that the shapes of the tubes are different from one car to the other. So, the part numbers would certainly be different.

Bob

[Robert R.]

Re: Help - Stock 74 BB A.I.R. (Smog) Tube Confusion

Vic,

Here are some pictures of the tubes from my cars. From first to last they are: big block left, big block right, small block left and small block right. It is difficult to get a good shot since there are obstructions but you can see that the small block tubes look exactly like the ones that are depicted in the AIM.

I hope this helps.

Bob

[Robert R.]

Re: Help - Stock 74 BB A.I.R. (Smog) Tube Confusion

Vic,

Apparently, the editor reversed the pictures. The proper order is: small block right, small block left, big block right and big block left.

Bob

[Victor S.]

Re: Help - Stock 74 BB A.I.R. (Smog) Tube Confusion

Thanks you so much Robert - that really helps!!

[Joe L.]

Re: Help - Stock 74 BB A.I.R. (Smog) Tube Confusion

Vic,

I happen to own 2 '74 Corvettes. I am the original owner of my L-48 Coupe and the second owner since 1993 of an original 19,000 mile big block convertible. I just looked at both cars and will verify that the shapes of the tubes are different from one car to the other. So, the part numbers would certainly be different.

Bob

Bob------


The tubes for the small block were definitely different than for the big block; there's no way the tubes can be interchanged.

However, for big blocks there were two different types of tubes but the part numbers were the same for each type. One of two things must have occurred to account for the differences: either the GM drawing allowed manufacturers to make either type or some 1973-74 with LS-4 were actually fitted with the earlier GM #3981061/3981064 tubes. The tubes shown in your pictures have the "crimped" connection between the larger diameter center tubes and the smaller diameter end tubes. The other style has "tapered" connections between the larger center tube and the smaller end tubes.

The "tapered" style is seen below. I believe that both types have been observed on original cars.

[Robert R.]

Re: Help - Stock 74 BB A.I.R. (Smog) Tube Confusion

Joe,

Thanks for the clarification. I agree that both styles may be seen on original cars. Maybe it is determined by the date of manufacture. My big block is 4/25/74 and my small block is 1/21/74. I know that my small block tubes are original to the car since I removed them shortly after I took delivery in '74. I saved them and reinstalled them when I did a body off resto in the late 80's-early 90's. I am also positive that the big block tubes are original to the car even though I am the second owner.

Bob

[Joe L.]

Re: Help - Stock 74 BB A.I.R. (Smog) Tube Confusion

All-----


Just to be clear, while the "tapered" junction tubes were used for some big blocks in the 1973-74 period, they were not used earlier. The 73-74 tubes can be used to SERVICE earlier big blocks. However, I believe there is another slight difference in the 73-74 tubes versus earlier. In that regard, I believe that the left side tube assembly has a slightly longer curved inlet neck in the earlier tubes.
Over the 1966-74 period, there were actually 4 different part numbers for the left side tubes and 3 different part numbers for the right side tubes. Not all were officially supersessive to the earlier but the GM #333823/333824 tubes can be used for any 1966-74 big block application. All the tubes are long-since GM discontinued. I believe that only the 73-74 style with "tapered" junction tubes are currently available in reproduction but it's possible the earlier style are still reproduced.

For small block tubes, I don't know of any 1966-74 tubes that had anything but the "crimped" junction tube. I don't think that later did, either, but it's possible they did.

By the way, these tubes are not "forever" pieces. Exhaust heat will eventually deteriorate the section of the tubes between the manifold and the check valve, sometimes causing the tube to break in the area of the manifold. This condition might not be readily apparent, though.

In a related matter, the check valves at the top of the pipe assemblies, at the interface of the pipe and hose are not "forever" pieces, either. These are often sold in used, replated condition as "re-manufactured". There's no way to functionally "re-manufacture" these valves. So, when one buys a "re-manufactured" valve in order to achieve original configuration (including stamped number), one is buying a part that already has some of its life "used up". How much? One finds that out when the valve fails. So what, you say? Well, when either of the valves fail the result is the destruction of the diverter valve and AIR pump. How do you know that one has failed if you don't check them for one way functionality? You find out when the diverter valve or pump fails. Diverter valves can be "pricey", to say the least.

[Tom R.]

Re: Help - Stock 74 BB A.I.R. (Smog) Tube Confusion

The "tapered" style is seen below. I believe that both types have been observed on original cars.

Hey Joe

Of course this is of great interest given our review and revision of the 73/74 TIMJG. Are the photos of the tapered tubes, NOS. I may want to use to illustrate the tapered version of the pipes.

[Joe L.]

Re: Help - Stock 74 BB A.I.R. (Smog) Tube Confusion

Hey Joe

Of course this is of great interest given our review and revision of the 73/74 TIMJG. Are the photos of the tapered tubes, NOS. I may want to use to illustrate the tapered version of the pipes.

Tom------


No, this is a reproduction. I just used it to illustrate the style of connection which is the same for original versus reproduction. I have NOS examples of both pipes but they are a lot more difficult for me to get at than the reproductions. I may try to get at them later if it's important.