74 Big Block

[Justin Abbott]

I have a 74 454 which is almost completely done. I have a question on the AIR system though, the JM says that only the CA 454 cars had AIR but my manifolds have bolts in them where they look like they had tubes at one time. Now my car is not a CA car so which is correct. Where all the manifolds drilled anyways and if so what type of plug did they have in them.

[Jack H.]

Re: 74 Big Block

From your copy of the '73-74 NCRS JG book:

"LS4 exhaust manifolds are not interchangeable and are cast iron. All are tapped for A.I.R. injectors...."

In earlier years it was common for two versions of exhaust mani's to be made (one with holes drilled/tapped for A.I.R. and a second with without them). Looks like somebody did a cost analysis and decided making one version (with the holes) and then plugging the holes when the engine didn't use the A.I.R. system was more cost effective than making and inventoring two different versions....

[Terry M.]

Re: 74 Big Block

I doubt GM would have used bolts to plug the unused holes in the exhaust manifolds. During 1970 some big block exhaust manifolds that had been drilled and tapped for AIR fittings were used on engines that did not require the AIR system, those were plugged with a unique plug that is consistent with the unusual threads in those holes. I would expect nothing more pedestrian in 1974.

[Harmon C.]

Hmmm

If the holes are pluged and you have a turbo 400 automatic you are good to go. Should you have a four speed look for a big deduction if you show up on the judging field without AIR installed in any 74 Fed. or Ca.

Lyle

[Joe L.]

Re: 74 Big Block

Justin-----

ALL 1974 Corvettes with LS-4, regardless of where originally delivered or how otherwise optioned, were originally equipped with the air injection reactor system (AIR). As a matter of fact, the only 1974 Corvettes which were not equipped with AIR were L-48 automatics with federal emissions (engine suffix code "CLA").

[Justin Abbott]

Re: 74 Big Block

That does not correspond to the JM, all 73's had it, but in 74 and big block it say otherwise. Is there a jusdge out there that can determine which it is supposed to be.
Thanks

[Harmon C.]

Re: 74 Big Block

Justin
I quoted the latest manual with my information. I would check the emissions label near the power brake boster and see if it looks original and says AIR.
Lyle

[Joe L.]

Re: 74 Big Block

Justin------

I feel pretty confident that the JG is incorrect if it says that any 1974 with LS-4 was not originally equipped with AIR.

First of all, as Lyle mentioned, check the emissions label if it's still present. If it's coded "ZH" or "ZJ", the car originally had AIR. Guaranteed. Period. Those are the only 2 codes that I know of that were used for 1974 LS-4. Of course, there may have been others, but I would strongly expect that, if there were, they also represent AIR-equipped emissions systems.

Second of all, as Terry mentioned, in those relatively rare cases when manifolds with AIR fittings were used on non-AIR applications, special plugs were installed in the fittings. These plugs are not hardware store items. In fact, any head configuration plugs using this special thread are difficult to find and won't be found in ANY hardware store. If the plugs on your manifold are square external head, hex head, or are made of brass, those plugs were NEVER installed at a GM engine plant or St. Louis. Never, ever!

[Tom R.]

Re: 74 Big Block

Justin:

What's correct? Lyle suggested reviewing your label that I suspect carries the broadcast code of ZH and a part number 346213. I take it the engine suffix on your block is either CWM (4 spd) or CWR (M40). ZJ was reserved for CA Corvettes but were emission equipped identical to the Corvettes carrying a ZH emission label.

The label will read at the top just to the right of center AIR-EGR EXhaust Emission Control. The emission label is an emissions compliance label and conforms to the EPA emission regulations in 1974. The AIR EGR Exhaust describes the equipment installed on the vehicle that causes compliance with the EPA emission requirements for 1974...this is where Lyle is stating that if it (a 454) shows up without AIR, it gets dinged.

Also, Joe L is the SME (subject matter expert)and delaring how big block Corvettes were emission equipped in 1974. I'm a mere 73-77 student and agree with both...Lyle (a senior level judge...chronologically has done a lot of chassis/mechanical judging so knows his way around 73-74 engine compartments. Trust these guys.

[Tom R.]

Re: 74 Emission Labels

I've got copies of all 74 emission labels and they collectively describe AIR EGR equipment on all motor/tranny configurations except The CLA 350/195 L48 M40. The 73-77 manual has a number of statements that do not reconcile with what has become typical on those Corvettes judged at NCRS events. AIR configurations is one such item that is not consistent with what is seen and therefore contributes to an emerging consensus that the manual is incorrect in this respect.

[Harmon C.]

Re: 74 Emission Labels

Tom
In 73-77 the smog pump is with the chassis judging which I have not done in years. I have seen very few 454-automatics if any so I usally check the book. I made a note of your findings in my copy of the TIM&JG. In 73-77 we need a complete list of when AIR should not be installed as this comes up very often off the judging field.
Lyle

[Justin Abbott]

Re: 74 Emission Labels

Well this has burst my bubble, Without even looking I am pretty sure it is ZH.
So now here I am 3 weeks from Carlisle and I need a A.I.R. system. Any chance anyone out there has one? The bolts in my manifolds are bolts as in hardware store bolts. That was originally the intent of this was to figure these out and find the correct plugs. However it appears that I am supposed to have A.I.R. Any chance or likleyhood that the JM is correct for 74. I had a 73 454 4spd and that had it.

[Harmon C.]

Re: 74 Emission Labels

Justin
I'm not sure why you need the A.I.R. system at Carlisle but you should be able to find some for sale. I found a picture of a ZH label that reads AIR. If their is a doubt if a Corvette should have AIR on the judging field we allways check the Emissions label as most of them are still the original label on 73-77 cars we see.

Lyle

[Justin Abbott]

Re: 74 Emission Labels

Lyle, I was planning on selling her at Carlisle. I have my eyes on a 69 400hp car so this one needs to go. You know how it is.
Thanks
Justin

[Harmon C.]

Re: 74 Emission Labels

Justin
That smog system will cost around $2000. and most buyers won't know or care if it is on the car so save your money. It took the best experts (not me) on this board to decide the manual must be wrong so I hope you can find a buyer.
Lyle