A.I.R. and my LT-1

[jmp]

As a preamble, let me just note that this conversation actually started off in BHP Explanation..., but since I was getting off track, I decided to start a new topic here. Check the link above for the beginning of this discussion on AIR and LT-1s!

Now, without fdurther ado....

I'm slightly po'd!

OK, let's get the minor things out of the way first.... I don't have the tire pressure sticker. I don't have the Canada export sticker. The car was imported into Canada, though, in August of '71. I have two copies of a GM Canada, dated April 28, 1998, that has my VIN number on it along with the option list, production date, shipping date, etc.

The option list includes L08 (Engine Emmission Certification), Z49 (Mandatory Canadian base equipment modifications), and ZK8 (Tire Pressure Sticker). Can anybody give me details on this?

Oh, btw, the doc also says atha only 1058 'vettes, 131 of them being LT-1s, were produced for sale in Canada.

OK... I looked at the emmissions sticker and it doesn't say anything terribly informative. Tom73, I'm not sure what you thought it might say that would help...

On to AIR. First, I looked up the exhaust manifold #s in my Restoration Guide and it gives two different #s for LT-1 exhaust manifolds in 1972:
3932461 for left and right
386711 for left and right

Second, I looked up the engine codes:
CKY: LT1 with Holley four-barrel, mechanical lifters, and four speed (my car, btw)
CRT: LT1 with Holley four-barrel, mechanical lifters, K19, and four speed.

Now this seems to contradict another portion of the book which states that all LT-1s in 70-72 were originally AIR equipped.

Third, I pulled the numbers from my exhaust manifolds. Both right and left say 3932461. I looked for the holes for the AIR fittings on the right-side manifold, but didn't find any -- they're not there. Just for fun, though, I took a anotherlook at the left manifold too. At first I thought that the holes for the fittings weren't on that manifold either, but when I looked closer I realized that the holes were there -- they were just plugged!

It appears as though this engine has gone through a significant rebuild sometime in the past -- maybe when the block was cracked! But when it was put back together, somebody got left and right mixed up: the exhaust manifolds and the valve covers are both mixed up!

Well, I'm still not sure. The manifolds look like they should have an AIR system attached, but my Restoration Guide says that the CRT engine and not the CKY engine had K19 (A.I.R.). Hmm... thinking about it though, I'm not sure why I think my car is the CKY. As I said, it's a new block, so there is no code stamped onto the block (other than the casting number).

Is there anyother place that the CKY/CRT code would show up?

 

[jmp]

more AIR questions

Assuming my car was AIR equipped originally, I'd like to get it back that way. What parts will I need? I guess I have the correct manifolds, so I don't have to worry 'bout that. Other than those, I think I'll need:
AIR pump
belt
bracket
hoses and fittings

Looking at Ecklers, I see that they have a pump ($74), small block exhaust manifold AIR tube assemblies (#44333, $115 pr), right AIR manifold tube with small block (#31492, $38) and an AIR check valve ($24).

They also have an AIR replacement kit for $500, but I don't know what that includes.

 

[jmp]

Hey, wait a sec!! Do the AIR pump hoses connect to both exhaust manifolds? I've just seen a pic that makes it look that way. In that case, why does only one of my exhaust manifolds have (plugged) holes for the AIR fittings???

:confused

(I wonder if this should be posted in the general C3 tech area. Is there a way to cross post?)

 

[vettepilot]

JMP...
If the rocker arm covers are not on the correct side you may have another small problem. If my memory serves me correctly, the cast covers had small tabs cast into the underside of the inside to catch and drip oil onto the rocker balls. This was done to increase the lubrication of the rocker arm ball in the solid lifter engines because of the higher RPM potential of those engines. That was one reason so many guys, (like me) bought the cast covers when building small blocks. Not only did they look great compared to the stamped steel units, but were truly functional in respect to increasing lubrication to the rocker balls, and cooling the oil that was splashed onto the inside surface. So if they were placed on the wrong sides, the tabs may not be sitting over the rocker balls correctly. Just a thought for you to check on.
vettepilot

 

[jmp]

ad

Arg! Another thing to worry 'bout! But easy to fix, I guess. However, I think I asked this question before (does it matter that they are switched) and somebody said 'no'. Well, like I said, easy to fix...

 

[RalleyRed]

jmp,

From what I've read all 72's have A.I.R. including the ZR-1, further I believe and someone correct me if I'm wrong, the 1970 350/350 is the only seventies Vette that for some reason didn't have A.I.R. .

The only other place I know of that you may find your engine code would be on the tank sticker.

As to the A.I.R. systems you can buy.... From what I've heard the aftermarket makes a functional replacement, but it won't look right by any means. Last I knew they were blue in color!

Personally unless you need it for an inspection or you were going to find yourself a correct replacement block and do a full restoration ( maybe for judging) I wouldn't bother.

If you do feel the need though, I'd pick up a copy of Hemming's Motor news and find a correct setup from one of the vendors.

Rick

 

[RalleyRed]

jmp,

I just went back to the BHP post and had to come back and tell you that , that is a sweet looking motor compartment.

Rick

 

[jmp]

jmp,

I just went back to the BHP post and had to come back and tell you that , that is a sweet looking motor compartment.

Rick

Thanks! I can't take any credit for it though -- I inherited it this way.

Problem is, I don't know what's been done to it!!! It's looking like AIR has been removed and that some things have been switched left to right. The distributor's been changed to convert the points, using a Pertronix Ignitor system. I'm beginning to wonder if the original carb -- I've changed it to a Holley Street Avenger -- is actually correct. The air cleaner is not original. The block is not original.

All this I know, but what don't I know. The more I look, the more I discover. I'm taking a closer look at the service receipts that I inherited with the car and I've found some that are "interesting": looks like the car's got new pistons, bearings, valve springs, rocker arms, engine mounts, starter... And some other work has been done on it: right side exhaust manifold has been filed straight, the "vac. hoses, P.C. hose, vac. booster hose etc." have been rerouted, and (the big ones) block has been bored, the crank reground, and the heads have been rebuilt and surfaced.

I'm going to have to track down some of the previous owners and find out what's happened to my baby!

 

[Tom73]

One note about the exhaust manifolds, they are interchangable from side to side, no left or right. Sounds as if one of your was replaced at one time. Maybe since they had removed the A.I.R. system they used a manifold that did not have the AIR holes?

In the Corvette Black Book, it list the CRT engine as uncertain usage. So it may or may not have ever been used in a Vette. May have been a code that was planed to be used but never made it to production.

tom...

 

[jmp]

But what about the manifold casting numbers. You'd think if both manifold numbers were the same, then both manifolds would be the same!!!

Time to take the 'vette into the shop, and get an 'expert' opinion! At least, from an export who can see the car with his own eyes!

 

[JohnZ]

But what about the manifold casting numbers. You'd think if both manifold numbers were the same, then both manifolds would be the same!!!

Casting numbers are just that - the identification of the raw casting as it comes out of the mold at the foundry; subsequent machining operations end up creating different finished PART numbers in many cases (which are not on the parts), incuding these CASTING #3932461 manifolds (or 386711, which were used on a small number of cars instead of 3932461). The 461 casting was used on both sides from 1969-1974, machined for (4) A.I.R. fittings, and was used again from 1977-1979 with (2) A.I.R. holes on the right side (different PART number) and (4) on the left side. In 1980, both sides were machined for (4) A.I.R. holes.

 

[jmp]

Crap! Still leaves me with more questions! :confused

OK, gotchya 'bout the casting numbers. But you didn't mention the 461 not being machined for any AIR fittings. Did this happen?

I'm going to triple check and maybe take some pics, but I'm pretty positive that one side (currently the left side) has 4 holes, and the other side (currently the right side) has 0 holes, but both are the 461 manifolds.

 

[Tom Bryant]

As John said raw castings find their way onto many applications with different machining operations. You can almost bet that some other Chevy car or truck uses the 461 manifold without the A.I.R. holes. I worked in the parts dept of a large Chevy dealer at the time and I can't recall any manual transmission V8s in this time period that didn't have A.I.R. Many if not most auto trans cars didn't. Complete original correct numbers A.I.R. systems are very expensive as they are sought by the restorers that have to have the right parts.

Since you don't have the original block installing this garbage is pointless. I'm sorry, but it was garbage when it was new and it hasn't improved any over the years. The pumps went out and had to be replaced way too often. The diverter valves on the pumps failed like clockwork. This caused a backfire every time you let off of the gas to shift. This in turn blew the baffles loose in the mufflers. The tubes that mount on the manifolds rusted out and the check valves that mounted on the tubes rusted out at an even higher rate. Then they were seized to the tubes and often required replacing both parts anyway. As was said above, unless you are going to find a numbers correct block and go for the Gold or Top Flight judgings you are better off without the A.I.R.

This system was just a stop gap measure because GM didn't have the technology to meet the new emissions standards so they settled on blowing oxygen into the exhaust manifold to complete the burning process. This, BTW, increased exhaust manifold temps to the point where cracking became common. Another drawback.

As for your carb, check on the front of the choke housing for these numbers. R6239A 3999263. the R number is a Holley number and the long number is GM. I'm not that familliar with GM Holleys to tell you for sure if both of those numbers will be there.

Tom

 

[Billy]

A.I.R. and LT-1

Jim,

From the research I've done, all '72 LT-1's were equipped with A.I.R. I've also heard some people comment that GM installed A.I.R. to motors due to a performance gain - the claim the colder air helps contract the hot exhaust gasses for a less restrictive flow through the exhaust....not sure I believe that though. I own a '72 LT-1, #000085. It has the CRT engine. I've been researching this topic and have yet to find out the difference between the CRT and CKY.

 

[Tom Bryant]

Re: A.I.R. and LT-1

Hi Jim,

Welcome to the Corvette Action Center and the LT1 Registry. That's a nice collection of Corvettes you have. How about some pictures when you have time?

Jim,

I've also heard some people comment that GM installed A.I.R. to motors due to a performance gain - the claim the colder air helps contract the hot exhaust gasses for a less restrictive flow through the exhaust....not sure I believe that though.

I don't blame you for not believing that. That theory might have some credence if we were dealing with a non-flamable gas. The exhaust , as it exits the cumbustiion chamber, consists of super heated burnt fuel, some heated unburnt fuel and the tail end of the cumbustion flame. There also will be some fresh fuel/air mix from the intake system that blows straight throught the cumbustion chamber due to camshaft overlap (the brief period of cam timing when both intake and exhaust valves are open at the same time). The reason for the unburnt fuel in the exhaust is that all of the oxygen has been consumed and the small amount added by camshaft overlap isn't enough to continue the burn by itself. (Nitros Oxide anyone?) When this unburnt fuel exits the tail pipe we have bad emissions (hydrocarbons ect.). So to lower these bad emissions the A.I.R. system injects air into the exhaust manifold right at the exhaust port to take advantage of the remainder of the cumbustion flame and the superheated unburned fuel to continue the burn process. It is important to continue the burn for a smooth and uninterupted cycle as opposed to a secondary cumbustion in the exhaust manifold which would be a backfire.

As you can see this whole process of continuing the burn in the exhaust manifold expands the exhaust gasses due to heating and does not contract it. This will cause additional backpressure and even reversion of some burnt gasses back into the combustion chamber diluting the intake charge and hurting power production. Also we have the further parasitic loss in horsepower of having yet another accessory being driven off of the crankshaft by a V-belt.

Bottom line is the only reason these devices were on the engine was to meet Federal Emissions Standards and the engine suffered because of it. You wouldn't believe how many guys thought they could route these A.I.R. tubes into the air cleaner for a mimi-supercharger effect. :L

I hope this helps clear up the reason for the A.I.R. system

Tom

 

[Billy]

LT-1 CRT ENGINE

Thanks for the reply Tom.

I agree with your reasoning on the A.I.R. system. Any thoughts on the CRT engine code? I've had some correspondence with someone at the N.C.R.S. and still owe him some photos of the stamp pad. From everything I've researched so far this is the only CRT 72' LT-1 documented............

 

[Tom Bryant]

Re: LT-1 CRT ENGINE

Thanks for the reply Tom.

I agree with your reasoning on the A.I.R. system. Any thoughts on the CRT engine code? I've had some correspondence with someone at the N.C.R.S. and still owe him some photos of the stamp pad. From everything I've researched so far this is the only CRT 72' LT-1 documented............

Is your car a late production? I'm sure there are others that are more familiar with the LT1 than I am that may have already formed an opinion on this. We know that in prior years the LT1 had A.I.R. but there wasn't any specific mention of it in the engine code lists. Probably because they all had it so there was no reason to list it seperately.

This is strictly a speculation but maybe Chevy was getting ready to offer the LT1 with an automatic for late '72 or possibly '73 so they changed the code for the 4 speed car to CRT and a new code for the auto car would have been produced for LT1s without A.I.R.(since automatic cars usually didn't have A.I.R.) but this never happened. Maybe because for '73 they put a Q-Jet and hydraulic cam on basically the same engine and called it a L82 and with the milder cam profile avoided having to use the A.I.R. altogether (except maybe in CA which I'm not sure of). this is an interesting subject. Maybe we will never know for sure.

Tom

 

[Billy]

Tom,

no. actually this car is very early production - serial #00085, which might still suggest corporate testing. I also know that to date this is the earliest LT-1 listed by the N.C.R.S.......

 

[72LT1Steve]

Re: A.I.R. and LT-1

Jim,

From the research I've done, all '72 LT-1's were equipped with A.I.R. I own a '72 LT-1, #000085. It has the CRT engine. I've been researching this topic and have yet to find out the difference between the CRT and CKY.

Billy; I think I will always be confused as to this A.I.R. thing. But your motor CRT designation is I believe more on the rarely used/seen side of things. I seem to remember the majority of folks having the CKY stamping (mine as well). Your CRT stamping does indicate the 350ci, 255hp, w/A.I.R. system usage on your car along with a Manual Trans. My car having the CKY stamping only has a two groved pully, but the original exhaust manifolds do have the A.I.R. holes, only plugged. I'm so confused

Steve

 

[Tom Bryant]

I agree that the CRT stamping is confusing. We may never know just what the deal is unless we can find more examples to compare against each other.

Tom