What is this shield for?

[Already Gone]

Looking under my hood I see these two "shields" one on each side of the engine near the exhaust manifolds. My truck is pretty original especially under the hood so I'm curious as to what these do or did ?

[67swb72klb]

extra air flow for the rear cylinders
not too many around anymore

[engineer_gregh]

I've always heard them referred to as air horns. I'm not certain what their function was but to find them still in place is rare, at least the several hundred or so trucks I've looked at:-)

[Lee H]

I wonder if they were to help keep the exhaust manifolds cool. I've came across many of these cracked manifolds at my local pick a parts, mostly on C20s and camper specials.

[Already Gone]

Originally Posted by 67swb72klb

extra air flow for the rear cylinders
not too many around anymore

Why? Cooling ?

[DeadheadNM]

Subscribed - haven't seen these before. Haven't noticed any on the "Survivor" engine thread but may have missed them.

[too much stuff]

Originally Posted by Lee H

I wonder if they were to help keep the exhaust manifolds cool. I've came across many of these cracked manifolds at my local pick a parts, mostly on C20s and camper specials.

I believe this is correct...

[leddzepp]

I see them on trucks all the time. I believe they are to help direct airflow to cool the manifolds as LeeH stated.

[DeadheadNM]

Would 4wd's make use of these? Given a 4wd motor is set back vs. 2wd it appears clearance would become an issue from what the pics show.

[Already Gone]

If they are to cool the exhaust manifold it blows me away how an engineer would design something like that. My truck has Ram Horns and if I'm not mistaken they had been around for a while by 1972 so GM must have had some prematurely exhaust manifold burn outs to come up with something like this.

[FirstOwner69]

Here are a few other threads. Sounds like they may be a 1972 small block thing.

http://67-72chevytrucks.com/vboard/s...d.php?t=314684

http://67-72chevytrucks.com/vboard/s...d.php?t=208380

http://67-72chevytrucks.com/vboard/s...d.php?t=477584

[Already Gone]

Well so far nothing definitive form this post or any previous post. Cooling the exhaust manifold makes the most sense to me. I guess everyone including me assumes the two holes in the top of these things are for bolting something to them but if if they are shields then those holes are probably there to let air in or out of the shields. If they could be found in service or parts manual we'd have name and that should in positively identifying what they are.

[72MARIO]

My original 1972 had them. Now that I know what there for I wish I kept them

[Keith Seymore]

Originally Posted by Already Gone

I guess everyone including me assumes the two holes in the top of these things are for bolting something to them but if if they are shields then those holes are probably there to let air in or out of the shields.

Looks to me like the same part is used on both sides.

The holes on top are simply the attaching holes on what becomes the bottom for when it is installed on the other side.

I think "air deflector" would be a more accurate term than "heat shield".

K

[brown7373]

The holes on the top do not line-up with the holes on the bottom. I think they were designed to make it more difficult to remove the middle 2 spark plugs. Mine are still there and they are a pain.

[71 super]

They are air deflectors for the manifolds as stated, and they did not come on big blocks or 4x4 trucks. They were a late addition around 71 and most were removed because they are in the way of almost everything.

[Lees68GMC]

This Shield protects my Vortec 5.3s aluminum oil pan from rocks and other destructive potentials, home made not OEM

[Keith Seymore]

Originally Posted by brown7373

The holes on the top do not line-up with the holes on the bottom.

Try swapping 'em side for side and see if it works.



K

[Cash3481]

I think it may be a deeper thinking concept too. The airflow comes through the engine bay and hits the motor causing turbulence so these may be to direct air creating a draft across the manifold. (increasing velocity maybe?)
I have seen them a lot on trucks here in the Midwest.
Its just been my thoughts... I have no idea if its true.
They are in the way for almost any thing you wanted to do for sure. LOL

[mechanicalman]

Originally Posted by Lee H

I wonder if they were to help keep the exhaust manifolds cool. I've came across many of these cracked manifolds at my local pick a parts, mostly on C20s and camper specials.

That appears to be a R hand manifold, unless the photo is reversed. On my 72 the L manifold did that, but I assumed it was because of the "hot air" tube sucking cold air across the hot manifold, and it was not equipped with a heat riser (EFE valve) from the factory but it did have an emissions device that locked out the vacuum advance when the engine was cold or until it hit 3rd gear so that I think might overheat the exhaust gasses.

So, on the R manifold, did you notice if the vehicles that had the cracked R manifold have a heat riser valve?

Just curious why this happens. I've see AIR cause this on big blocks.

[Lee H]

Originally Posted by mechanicalman

That appears to be a R hand manifold, unless the photo is reversed. On my 72 the L manifold did that, but I assumed it was because of the "hot air" tube sucking cold air across the hot manifold, and it was not equipped with a heat riser (EFE valve) from the factory but it did have an emissions device that locked out the vacuum advance when the engine was cold or until it hit 3rd gear so that I think might overheat the exhaust gasses.

So, on the R manifold, did you notice if the vehicles that had the cracked R manifold have a heat riser valve?

Just curious why this happens. I've see AIR cause this on big blocks.

Never paid that much attention but have always speculated it was from heavy towing/hauling heating up the manifold. I remember our tractors manifolds would be cherry red during spring plowing, and fall turning. Just assumed it was about the same thing with heavy towing and hauling with a truck.

[VetteVet]

I think what you're looking at are the manifold covers that are part of the heat stove system used to keep the intake air from frosting up. The hot air around the manifold rises up the tube into the air cleaner and a valve in the cleaner opens to let the warm air into the intake stream.

Here are some pictures.

[Already Gone]

Originally Posted by VetteVet

I think what you're looking at are the manifold covers that are part of the heat stove system used to keep the intake air from frosting up. The hot air around the manifold rises up the tube into the air cleaner and a valve in the cleaner opens to let the warm air into the intake stream.

Here are some pictures.

Attachment 1335652

If you look at the the first post with the pictures on the top row of pics the far right one hows the heat tube intact on the truck.

[VetteVet]

I see that in the third picture down it shows the heat stove mounted on the manifold cover and your shield down below it. also on the passenger side there is another shield similar to the left side so they are not part of the heat stove system. I'll have to defer to the other posters for the answer. VV

[leddzepp]

Originally Posted by 71 super

They are air deflectors for the manifolds as stated, and they did not come on big blocks or 4x4 trucks. They were a late addition around 71 and most were removed because they are in the way of almost everything.

Thanks for the confirmation Harold