1975 Emission Control Equip new information

[Joe L.]

Re: 1975 Smog Equipped Corvettes

Tom-----

For 1975, there were only TWO engine options available for Corvettes----L-48 and L-82. No others that I'm aware of. There were THREE emissions certifications. The "AS" was used for non-California L-48s. The "AU" was used for L-82s. This may have been limited to just federal L-82s. The "DR" code was used for California L-48s. It may also have been used for California L-82s.

In any event, all 3 of the above codes include AIR as part of the emissions system included with that code.

[Tom R.]

Re: 1975's Delivered to California

Joe:
So, if I understand emission certification correctly, the sticker documents the emission control devices (systems) configured for that particular vehicle. The engine suffix also dictates a particular emission configuration and this should be consistent with the emission certification code label.

[Harmon C.]

Re: 1975's Delivered to California

I have the 73-74 TIG and it has the correct info on 74's with M40 no smog as you stated. I checked the driveline and it showed the second edtion 75-77 which I quoted as the issue they are selling but I heard their is a new one out or will be soon and I do not know if the smog information was changed. Lyle

[Bill E.]

Re: 1975 Emission Control Equip new information

Joe:

Thanks that's clear enough even for me to understand.

As to the original question as to whether 75's L-48, automatic with air have A.I.R. Tom Russo's response to Lyle on Monday seems to say that one has to look at what's there and see if you can tell if anything has been removed because there is no absolute way of knowing from the emission sticker or published information. Do you agree?

Bill

[Joe L.]

Re: 1975's Delivered to California

Tom-----

The emissions certification and sticker defines a particular emissions certification AND the particular emissions systems used with that certification.

The engine suffix code defines a particular engine configuration as-delivered from the engine plant, not necessarily a particular emissions configuration. It is possible that more than one emissions-certified engine could be built-up at the vehicle assembly plant from the same suffix-coded engine. It would not be the norm, but it could happen.

[Joe L.]

Re: 1975 Emission Control Equip new information

Bill------

If the ORIGINAL emissions CERTIFICATION label is on the car, it's very easy to tell what emissions control systems were ORIGINALLY installed on the car.

If there is NO emissions label on the car, then all one knows is that the emissions control certification had to be among those used that model year. Further inspection of installed components (i.e. engine RPO, installed transmission, engine suffix code, etc.) may be able to narrow down which codes that might be applicable to that particular car. Once (and IF) one figures out which code was applicable, one knows what emissions control equipment was installed.

By the way, 1968-1972 emissions control certifications, codes, and labels do not specify which emissions equipment was installed with a particular code. That practice did not begin until 1973. However, I have the emissions systems information for 68-72 models.

[Paul B.]

Need to get info on parts right, GUYS!!!

I believe EVERY '75 Corvette came with A.I.R. Every '75 I looked at(that was original enough to tell)THERE WAS EVIDENCE OF A SMOG PUMP AT ONE TIME!!! I have seen documentation from GM that "stated" "ALL 1975 Corvettes came with A.I.R", plus the same statement for EGR, EFE, catalytic converter. Also, 1975 AND 1976 CORVETTES WITH A.I.R. "DID NOT" come with those familiar bagpipes most people in this thread mentioned. '75 & '76 Corvettes with A.I.R. had a single hose off of the smog pump down to a nipple welded to the right exhaust pipe below the heat riser, so these manifolds LOOK LIKE '74 non-A.I.R. manifolds!!! They DO NOT have plugs or hole to put plugs into to begin with!!!

[Tom R.]

Re: Why!

Why?

[Harmon C.]

Re: Need to get info on parts right, GUYS!!!

Paul I checked my 75 Bow Tie pictures and see they are as you said no plugs never was in the exhast manifolds. Thanks for the info. and congrats on the Top Flight. Lyle

[Joe L.]

Re: Need to get info on parts right, GUYS!!!

Paul-----

You are correct. The manifold-mounted AIR "trees" were not used for 1975. They were originally scheduled to be used, but the design was changed to better accomodate the requirements of the catalytic converter first used for the 1975 model year. For 1975 (and 1976), the diverter valve had a single output which injected air into the forward, right side exhaust pipe, below the manifold connection.

Consequently, I was mistaken when I referred to the liklihood of the manifolds being changed in this case. I was thinking that 1976 was the only year for this "odd-ball" AIR configuration, but as I check, I find that it "afflicted" 1975, as well. It reverted back to the "tree" arrangement for 1977+, though, for all engines equipped with AIR.

[Tom R.]

Re: Need to get info on parts right, GUYS!!!

Joe...you're alluding to an important tidbit of information that may explain why" all 75's were equipped with A.I.R. To meet increasingly strigent NOx emission requirements, GM may have felt all configurations required the extra shot of oxygen to complete the combustion process in the catalytic converter. In later years, we see the "pipe" that feeds the cat converter.

I just read through a report from the late 70's regarding the failure of selected emission systems to meet federal emission requirements. Among many other things, it underscored the test environment of those mid-70 years for auto emission technologies.

Paul, please keep in mind, Lyle and I are referencing the most recently published NCRS technical reference guide, which is the only published reference guide on Corvette emissions. This is the same guide you used this past weekend to judge 75-77 cars in Stone Mountain. We are not the only two using the guide and, I don't know about you, but I've received no addendum indicating its contents re emission systems are incorrect. In addition, I queried the team leader early this year and indications were that that listed in the manual is correct. I apologize we couldn't get into your head earlier on.

Joe's done a yeoman's job in showing patience while walking us through his rationale and justification why the manual in this respect fails to reflect reality. Now...I'm suspicious and will work to collect sufficent data to support these alternative observations and arrive at the same point you have arrived. We are here to share and learn...rather than burn! Obviously, you've done quite a bit of research among C3 mid-years and its appreciated.