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Old 03-19-2013, 05:56 PM
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Thermostatic Air Cleaners & Smog

My Air Cleaner does not have the foil duct coming from the exhaust manifold like I've seen on so many other vehicles. The port is there on the air cleaner, and the air cleaner has the flap inside the intake. The flap is hooked up to vacuum via a single port the protrudes from the top of the intake. Also, the manifold does have a heat shield on it, but there is no provision for the foil duct on it, and no duct. I'm almost inclined to believe it never had it, as the last owner claimed it passed smog this way... However, the words of a salesman, if only a salesman for a day, mean little to me.

Is this duct required to pass smog? Is there a way to accommodate the use of one without having to change the heat shield? I would hate to have to search for one at the junkyard and swap it out, would really like to get this thing smogged and in my name tomorrow!

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Old 03-20-2013, 01:55 AM
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In CA I wouldn't be surprised if you needed to have it to pass. That said, I'm no authority on CA emissions- or emissions in general. But if you fill in the blanks (what type/make/year of the vehicle, engine size, etc.) and maybe a photo or two, we might be able to help.

But if you don't have a place on the exhaust manifold to pick up the heated air, the air filter housing might not even be original to that vehicle.

Generally, the vacuum source should be controlled by a temperature activated vacuum port, so the flap is closed during warm up (allowing warmed air to the carb) and open after it's warm. Usually the default setting (no vacuum applied) would be to have the flap open to allow cold air into the carb, but that's not always the case. If you look at how yours is working, you will see it is either always open or always closed with the engine running (and vacuum going to the vacuum motor on the snorkel). By disconnecting the vacuum line to it w/the engine running, then reconnecting it you can see if it's working at all. If the flapper is always closed when connected to the vacuum port (engine running), disconnect it to leave the flapper open.

Performance-wise, you can go w/o the thermo air cleaner assembly, providing the flap is open while the engine is running, and provided you're not driving in arctic conditions. But the smog police may say otherwise.
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Old 03-20-2013, 09:41 AM
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used car fix.

I've seed a soup can trimmed and fitted to the manifold shield with a couple pop rivets, then the foil flex tube installed, the inspectors will usually let an older car pass when replacements are not available but if it lookes right, paint it all black except the new foil flex tube.
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Old 03-20-2013, 10:55 AM
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Quote:
Originally Posted by Dizturbed One View Post
My Air Cleaner does not have the foil duct coming from the exhaust manifold like I've seen on so many other vehicles. The port is there on the air cleaner, and the air cleaner has the flap inside the intake. The flap is hooked up to vacuum via a single port the protrudes from the top of the intake. Also, the manifold does have a heat shield on it, but there is no provision for the foil duct on it, and no duct. I'm almost inclined to believe it never had it, as the last owner claimed it passed smog this way... However, the words of a salesman, if only a salesman for a day, mean little to me.

Is this duct required to pass smog? Is there a way to accommodate the use of one without having to change the heat shield? I would hate to have to search for one at the junkyard and swap it out, would really like to get this thing smogged and in my name tomorrow!
You always have two battles in California; one, will be the equipment that should be there. Two, will be passing the emissions test for gasses present in the exhaust. It is possible to pass the second one with parts missing such as the hot air stove to the air cleaner. On the other hand the tester may look under the hood, see the missing equipment and stop the test right there till you replace the missing equipment. I canít say which you'll encounter, apparently the previous owner got this past the equipment part and it passes the emissions part. You might not get that far if this is a different test station that you're going to.

The hot air inlet off the exhaust into the intake is only there to allow the use of a leaner mixture on cold starting. The dirtiest part of emissions and highest internal wear of engine parts is during the cold start enrichment phase (choke). The hot air stove is only there to reduce the effects and time it takes to transition through cold start. The flapper valve on the air cleaner is both vacuum and thermostatically sprung for control. The thermostatic spring opens the valve when the engine is cold allowing preheated air drawn over the fast to heat exhaust manifold into the carb or TBI. As the engine heats up internally the thermo spring closes the flapper valve so the engine only takes in unheated air for better power output when itís fully warmed up. The vacuum control is to force the flapper valve open if you demand maximum throttle while the engine is still cold, the assumption being this constitutes an emergency need for power where engine life is sacrificed to the greater good, whatever that may be.

Since the smog test isn't usually done on a cold engine, the lack of this device will not affect the gasses in the exhaust. Its absence is, however, an equipment issue; whether they make it so, or not, that I can't answer.

Bogie
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Old 03-20-2013, 12:16 PM
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exhaust heat from manifold

Cobalt is on track, inspector will see missing components and fail it right away. Been in the same mess, tin can and some patience will satisfy the smog test inspector. Had a none California 65 chevy truck without smog pump. Inspector made comment about it but the air cleaner was connected to the manifold for hot air to rise
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Old 03-20-2013, 06:35 PM
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Well, it's a 77 GMC Jimmy with 400 small block, TH350, and NP203 (AWD) in stock form. It has a GVWR of 6200 lbs, which put it in a different class of CA emissions, it is considered HD.

It only requires:
Thermostatic Air Cleaner
AIR Pump and lines
PCV valve
Charcoal Canister

It has true dual exhaust (came stock, but there are flowmaster 40 series on it now) and no catalytic converters.

It has all of the equipment needed. It seems to hold good vacuum too, I got 20hg out of it this morning when I fired it up, and it held well. New plugs and wires. New air cleaner. Going to change out a few vacuum hoses that look brittle. But I am worried because it has had carb problems. It hasn't done it lately, but it does have problems falling on its face when you first touch the gas occasionally. I do have a rebuilt unit, but have hesitated to put it on because I am an idiot when it comes to tuning a carb and am worried it will come out worse than the current configuration. This is only my second carb'ed vehicle ever. The first one was 15 years ago, I was 15 years old, lol.

I just want to get it all hooked up properly and tuned up the best I can before I take it in for it's first smog. If it doesn't pass, I don't want to be chasing equipment problems. I just want to handle whatever is thrown my way engine-wise and be done with it. Looks like I'll be rigging up some sort of way to hold the hose to the manifold I guess.
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Old 03-20-2013, 08:50 PM
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cal smog

if you decide to replace all vacuum lines and still have a burb in acceleration, take your carb to a shop that has a great rep that rebuilds YOUR carb. They machine and replace worn components. Rebuilt carbs are someones else's problem that was not fixed the first time (autozone)
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Old 03-25-2013, 03:28 PM
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Busy weekend, but I'm back to it now.

I don't think my truck has the right air cleaner on it. In the current configuration it wouldn't be able to run a foil tube from the air cleaner to the heat shield very easily. Everthing else looks to be in place and working, although I am going to go through it meticulously once I get this air cleaner figured out and working, it seems to be my only "missing" equipment

I was going to bite the bullet and simply buy a new replacement, figuring it would be a pretty common design into the 80's... But no. So I will make this one work. Anyone know of a bolt on fix by any chance? I am in apartments, and quite limited on what I can do.

I was thinking of looking for a bolt on heat shield riser (basically a heat shield that is made to fit the foil tube) that I've seen on many older vehicles, but can't remember what kind of vehicles had them. Hopefully many vehicles with 350's had them, and hopefully they should fit on my exhaust manifolds (400 cid), correct?

On another note, found out it is missing two intake bolts

Getting on that one while I chew on the air cleaner situation, any ideas are greatly appreciated
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Old 03-25-2013, 05:58 PM
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Quote:
Originally Posted by Dizturbed One View Post
Busy weekend, but I'm back to it now.

I don't think my truck has the right air cleaner on it. In the current configuration it wouldn't be able to run a foil tube from the air cleaner to the heat shield very easily. Everthing else looks to be in place and working, although I am going to go through it meticulously once I get this air cleaner figured out and working, it seems to be my only "missing" equipment

I was going to bite the bullet and simply buy a new replacement, figuring it would be a pretty common design into the 80's... But no. So I will make this one work. Anyone know of a bolt on fix by any chance? I am in apartments, and quite limited on what I can do.

I was thinking of looking for a bolt on heat shield riser (basically a heat shield that is made to fit the foil tube) that I've seen on many older vehicles, but can't remember what kind of vehicles had them. Hopefully many vehicles with 350's had them, and hopefully they should fit on my exhaust manifolds (400 cid), correct?

On another note, found out it is missing two intake bolts

Getting on that one while I chew on the air cleaner situation, any ideas are greatly appreciated
If the exh. manifold has a tin heat shield already on it, you can pop rivet a can to it to hook the foil tubing to. If done right you should be able to make it look convincing, even though it wouldn't be operational w/o the temp sensor(s) that mount to the filter housing (they route vacuum to the flapper vacuum motor at the appropriate time).

Because of how the smog test is done, that shouldn't effect the outcome as long as the flapper is in the open position and the engine fully warmed up.

But if there's no heat shield to mount anything on, you'll need to use something like the hot air choke kits, except on a larger scale. And I don't know of any kits made for the ThermAC setup, either.
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Old 03-27-2013, 01:36 AM
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Found it, listed for a Camaro, but should work just fine. Rivets right on, and looks very O.E. if you ask me, shouldn't get any flak for this Classic Industries | Restoration Parts | Mopar Parts | Camaro Parts | Firebird Parts | Nova Parts | Impala Parts | GM Truck Parts | Tri-Five Chevy Parts

Thanks for all the comments and help guys
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