Intake air regulated at 131°F / 55 °C !

[ikeepmychevytoo]

...this is according to the factory manual. Until last summer I was zooming about with sensor calibrated about 100 °F / 37 °C. Then I discovered this on the service manual and re-adjusted it accordingly to see what happens. Specs are very detailed like, heat door should crack open @ 100 °F, part-way open between 100 and 131, and should be completely open to outside air @ 131 °F. This is hotter than any climate!

Well, now it is more economical than ever. Technically too economical, because I was already getting the EPA milage with cooler air without fuss anyways. But now its kind of sluggish exactly after the warm-up. Propensity to knock under load started, which was of a complete absence until this warmer intake.

So for the first time, I tend to forget about "da original specs" and relocate the temp. to 100°F again. Afterall this was what I had been assuming suitable from a '72 AMC manual for years when no data was available at all.

What would be the engine cleanliness, would carbon build-up increase? or is it better just enrich the carburation and leave the temp at 131°F (I don't want to increase the variables, because adjusting these Varajets correctly is not possible with backyard equipment once tampered). Well, if you're still here, I guess I need some encouragement (or discouragement)

This is a GM 2.8 v6 (LE 2) with 8.5 compression from 1984 if matters.

 

[Harvey]

I kinda figure the engineer that build the motor knows more than I do, so I don't try to out smart them.

 

[mechtech2]

Do you have a carburetor?
You do need some heat, then.
If it were mine, I'd shoot for no more than 70-80F max of ingested air.

 

[eljefino]

Don't leave us out, man.

Is this car built to US spec with a computer and feedback carb with catylitic convertor and oxygen sensor? Or is it set up for leaded gas etc?

Have you a vacuum hose to your distributor or just wires?

I would not enrich the carb to take the warmer air and cure knocking. Nor would I retard timing. I'd go back to colder air first. Some stuff to try:

Run high-test fuel and drive aggressively to blow out the existing carbon...

Run techron fuel cleaner or do a water-down-the-throttle-body decarbonization...

Pull a spark plug to see how much build-up you have...

The current trend with fuel injected vehicles is to try for as cold air as possible but warm coolant inside the intake and around the combustion chamber. So if you want economy you might try a warmer water thermostat with that cooler air. Naturally you also want complete vaporization of your gas which is the point of the hot air intake.

 

[Gary Allan]

Well, I don't recall any heated air intakes on injected engines ..but I also was never aware that the sensor that typically was merely a passive vacuum switch in the air cleaner housing was adjustable. Now if it was driven by a bi-metal coil, like a choke, then with some tweaking you could alter it.

However, the last carb'd AMC I had (I forget the year) actually had a "summer-winter" setting on the heated air intake.

Back when the heated air intakes were introduced, the design was to provide 85°F air to the carb after, IIRC, 30-45 seconds of starting. I imagine that this wasn't always true in some place with a -30°F ambient temp ...nor do I suggest that this is the limit to the temp that it allowed.

 

[eljefino]

My 82 cadillac cimarron not only had the hot air stove but also an electrically heated plate under the carb. You could see when it turned off because the voltmeter would jump from 12v up to the normal 14.5 or so and the headlights would get bright again.

No wonder they went to throttle body injection on those little J-cars in 1983.

Oddly the TBI on my 91 dodge dakota and 94 spirit retained the "stove pipe" air heater. The spirit also had a coolant warmed intake and gave cabin heat within a minute.

 

[edhackett]

Quote:

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However, the last carb'd AMC I had (I forget the year) actually had a "summer-winter" setting on the heated air intake.

---

That's an easy one, Gary. Carb ice. You moved the lever to "winter" in cold temperatures to prevent the carb from icing up. My 1973 Toyota had this set-up as an optional "arctic air cleaner". When I removed it for an aftermarket air cleaner the carb would ice up anytime it was snowing and I have to stop about every 75 miles to let the carb melt out. Didn't take me long to replace the stock air cleaner.

Throttle bodies don't need the hot air(unless used for emission purposes) because they don't have enough of a venturi to cause icing. A carb can drop air temperature 40 F, so icing can be a problem starting at about 70F.

Ed

 

[Gary Allan]

This just appeared to bypass the normal flapper for the heat tube. That is, you had the thing open as it was supposed to in the winter ..and just avoided it in the summer. AMC was the only one that I ever saw this on. GM all had the thing work 24/7/365. Naturally, I didn't see too many Toyotas in the 70's

 

[ikeepmychevytoo]

Many thanks for everyone for the inputs.

Eljefino, actually this is a Canadian car. There are some emissions equipment on this but not as extensive as on the US versions. No cat., no air pump, no O2 sensor. Very basic EGR, vac advance etc. I also have that ceramic heater element under the carb. Carbon build-up is another variable, I cleaned it once to see what is going on. The knock in the idle relates to the carbon build up. Higher rev. "propensity to knock" (not really sounds like a problem) rather change in relation with the intake air temp. But I got your point, all relates.

Gary, yes, sensor is a vac. switch with bi-metallic spring and have a Phillips screw on it with a red marker dye... Although manual cites replacement, it is very easy to fine-tune once the tiny plastic shield removed. If this works out like I expected I'll particularly love that screw. This commoner of a Phillips screw crowd can be the hidden "econ vs. go" knob to play. I feel the potential.

I know, this is not scientific by any measure, just the temp. sounded high to me, in comparison to what I've ever seen. May be "current injection trends" also skewed my vision... 55°C is hotter than any climate. So Mechtech2's input of 80-85°F is encouraging. That's my point. Why this particular thing spec'ted at 131°F. I feel guilty for running this around 90° while the spec. is so high

I appreciate the hard to find background info on heated intakes. BTW, what is IIRC?

 

[TheTanSedan]

115F on early '70's Chev small block. Economy and performance run the same piece of track until the last moment. It's usually a mistake to change things in re engine life, fuel economy and reliability.

Better to re-time car for todays gas, borrow a wide-ratio exhaust gas meter to re-jet carb. Then time again. Leave the coolant and air inlet temps alone.