I have a 1971 XJ6 and I think this air filter is stock and of a sort used to meet emissions regs in USA.

I took it off today to clean out the inside and got a bit puzzled.

The air coming to the carbies I get, but some of the air, I assume, is meant to be diverted through the black tube and over the top of the engine to help with cooling (pic of disassembled tube shown).

As you'll see from the pictures there is a hinged flap inside, sitting in the closed position, closing off air from getting into the black tube.

I can move it with my fingers but it is a strong hinge/spring and needs a bit of force to open.

Does anyone know how this operates to open the flap and let air get across of the engine through the black tube? Further, how can I know if it is operating correctly?

I am asking both for curiosity's sake and because I am having some ongoing cooling issues: part of a bigger story and another post I plan to make.

Thank you for any insight you all might have.

 

You have a thermostatically controlled warm air intake, used to help with emissions in cold weather.

When you first start your car, the flap will be closed drawing warm air from around the exhaust manifold, through that tube, into the air cleaner.

That round puck thingy is the control module, usually connected to a temperature sensitive vacuum fitting plumbed into a water channel in the intake manifold. When the water gets warn enough it allows the vacuum to open the flap and take in cooler air from the engine compartment.

At least that's how it works on Mercan cars. As I drive a V8 Jaguar I couldn't say how the British did it.
(';')

 

Spot on Ellinor.

We had them down here also, and I have never seen one actually working.

That cross over tube is long gone on most I see these days.

 

Thank you, Grant! It's good to see you've returned.
In California it Must work if the car is equipped with it (they have a book to tell them), in order to pass SMOG.
(';')

 

A couple of thoughts:


1. Pre emission cars handled cold running or starting by enriching the mixture or "choking" off air resulting in a rich mixture that fired and ran more easily.


So, emission cars approached this by adding warm air to the mixture so it would vaporize better. LnrB describes that process well.


2. As Grant says, USA cars often have that , but not working. Except in smog states, it must work.


3. In CA, aftermarket air filters must be approved by CARB. The idea being to insure that this feature is present and working.


Side bar. EFI cars do it another way. Macht Nicht!!! my car has an after market filter of the oiled variety. One SMOG tech almost did not pass it as it had no CARB number??? But, as my car is EFI, the air flter has nothing to do with emission control!!!


4. As the car in question is of 71 vintage, it may not need to pass SMOG and this
hot air feature not needed.


5. Hot intake air is counter intuitive. A cold mixture is more dense, ie, more power, less throttle needed, less fuel burned, less emisions???? But, agree, it is more complex than that.


6. Kudos for seeking to understand the functions of stuff in one's car and elsewhere.


Carl

 

PS: A couple grew in numbers!!!!


Carl

 

The primary function of the warm air intake is to improve drivability during warm up. Cars of that era had 'leaned out' carbs in order to pass emission standards. These lean settings made the cars virtually undriveable while cold, no matter what was done with choke settings. Another factor, and again related to lean mixtures, was the potential for carb icing during winter weather.

In my ignorance and thinking that I knew better than all of the OEM engineers, I tossed the factory intake system of the mid-70s car that was my sole transportation at the time. About the third time the throttle froze part way open, I returned everything to stock config.

While emissions are the root cause, the warm air system is there as a crutch while the engine is not yet at normal operating temps. It is not there to improve emissions during warm up.

 

Thank you all for these great replies!

The last two winters in Baltimore have been super bitter so I think I'd like to get this working (following Mickey's thought) assuming it's possible (following Grant's thought!).

I don't know of an unused port on the manifold but there is a port under the secondary throttle housing (on a level with the front of the two carbies) where a tube from there has just been stuck on top of a screw by part of the transmission cooler system (please see picture). I've always been puzzled about that and now I wonder if it should be ported, not on that screw, but on what Ellinor descriptively calls the puck thing on the air filter housing (which to date hasn't been in use).

Could the secondary throttle have a port to convey the "information" to open the flap?

I know Ellinor thought it'd be on the intake manifold and I will follow up that suggestion tomorrow and see if I've missed a port there.

If I can get this rigged up, is it wishful thinking that once the flap opens extra cool air is crossing the engine and that could help with cooling?

Carl: In Maryland, no SMOG test required on classic cars... not yet anyway!
Thank you all!

 

Yes, that's wishful thinking. Air temps at the inlet have virtually no effect on coolant temps.

 

I wish it were otherwise, but thank you, Mikey.

 

You are quite right, Ellinor! Found another port far back on the manifold. Tube is sealed off with a brass screw. It's on a level with the rear carbie. (Picture included).

I had no idea it was there! I think I will hook it up and see if I can spot any differences.

Thank you so much.

 

Mikey:


OK, I get it.


But, cold engine drivability issues preceded SMOG patches by far.


Heating the intake manifold with exhaust gas was an early effort. Coolant passages in the intake another.


Henry's 32-48 V8's had a terrible exhaust path. But, it included a passage from the exhaust to under the intake and heat the air. I and others found this to be counter production of HP and "noise:!!


A copper penny fit in that opening in the block just right. One to a side. Now, all the exhaust gas went to the pipes. Two for a lot of us. Quirky when the engine was cold, true. But, once warmed, just fine. and a decided crackle in the exhaust.


All of us learned early on that cold air is more dense than warm air. applied in may ways:


1. Baseball players know that a well hit ball well travel further in hot air than in cold!!!


2. Engine folks, amateur or pro align intake to get cool air rather than hot air in the engine bay. As an Ic engine is an air pump ,that means a lot.


3. As a young army officer, I was in antiaircraft artillery. Our primitive fire control computer used meteorlogical data to compute the projectile's required flight path to hit the target. Balloons sent into the air did this.


4. Or just look at the smoke from a fire place. straight up or spread out horizontaly.


But, there many folks out there that understand this better than, I. you!!


Carl

 

Alright!! I'm glad you found it!

Oh, by the way, it's Elinor with only one "l." No worries though, an easy mistake.
(';')

 

Yup and they worked well until the smog requirements of the 70s caused the OEMs to add more widgets on top of widgets. Ah- the good old days!

 

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