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Old 12-09-2007, 08:28 AM   #1
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Hot/Warm Air Intake

Ok, I've got a question, and the search function didn't give me much in way of results. So, I'll start a new thread, and maybe a discussion.

I've read a bit here about hot/warm air intake. Appears that many are making heater boxes using the exhaust manifold. Obviously, you won't start out warm, and the temperature can vary.

Now for a what if...

Why not intake air through a section of the radiator? The radiator fins would provide a portion of filtration. Additionally, once the vehicle was warmed up, the temperature would stabilize and the air temperature that was being put into the engine might be regulated more consistently.

Just a thought. Feel free to flame me.

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Old 12-09-2007, 02:59 PM   #2
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it'll be more steady than from the exhaust manifold. I can think of advantages and disadvantages. it'll take a lot longer to get warm mainly.

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Old 12-09-2007, 04:12 PM   #3
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I just completed restoring and upgrading the WAI in my Volvo. Since it now includes a digital readout of airbox temperatures I've learned a few things I can pass on. By way of background, this setup, like most factory ones, uses a sheet metal shell over the exhaust manifold to gather exhaust heat into a duct that leads to the airbox.

Intake air temp (IAT) increases quite rapidly after startup. Temps here have been 25-40 deg. F since the project, and regardless of outdoor temps, IAT begins rising almost immediately after startup. I drive about 1/2 mile to get into I-95 and by the time I'm there temps have reached the mid-50's which is where they usually stabilize at. (I'd like to get it warmer but that's for later.)

I can't tell you what plumbing will work best on your car; I certainly could improve on what I've got here now. However I feel confident in recommending a digital thermometer for about $10. For low cost and little effort it will tell you what's happening with the IAT.

I got mine at Autozone. Saw similar ones on line at and at Advance Auto. It's an interior-exterior thermometer, also has a clock that I ignore. The exterior sensor is on a long wire lead that reaches to the airbox.

0) Plan routing path for the wire.
1) Cut wire. Just in case the sensor is polarized (plus and minus side), I cut the two leads within the wire at slightly different points. So that when rejoining, the same two wires are rejoined.
2) Drill 1/8" hole in airbox for the wire.
3) Mount sensor inside airbox; it comes with good double-stick material. Run the lead out hole in airbox.
4) Solder the wire lead back together. To protect the sensor from solder heat, I gripped the solder joint with pliers between solder location and the rest of the wire, to soak up any heat before it could get to the sensor. Rubber bands around pliers handles held a good grip without me holding on.
5) Run long wire lead back to instrument cluster and give display unit a home.

My lead runs through a joint recess in sheet metal where A-pillar and windshield base and hood all meet. If your car has no such groove you might need to run lead through a hole in firewall before soldering wire back together.

Definitely solder. Twisted wires or crimp connections will eventually corrode and thus give you false readings.
Currently getting +/- 50 mpg in fall weather. EPA is 31/39 so not too shabby. WAI, fuel cutoff switch, full belly pan, smooth wheel covers.

Now driving '97 Civic HX; tires ~ 50 psi. '89 Volvo 240 = semi-retired.
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Old 12-09-2007, 05:50 PM   #4
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You won't get hot air from the radiator until the thermostat opens. Also the air won't be very warm in the winter. To get warm air sooner I want to put a small heater core in the bypass circuit. This is the circuit that allows water to flow through the block and water pump when the thermostat is still closed. You might use the heater hoses also. I bought a small heater core to build such a system but looking at my track record on recent projects that may not happen.

The collector around the exhaust may be the best idea.
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Old 12-10-2007, 05:42 AM   #5
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True about radiator air being cold for a few minutes.
However I tested that air and found 80-110 degrees with engine warm when outside was maybe 45 deg. F.

So don't discount radiator output air completely, though it might need some controls to block it from the intake path or adjust the overall intake air temp (IAT) to where you want it.
Currently getting +/- 50 mpg in fall weather. EPA is 31/39 so not too shabby. WAI, fuel cutoff switch, full belly pan, smooth wheel covers.

Now driving '97 Civic HX; tires ~ 50 psi. '89 Volvo 240 = semi-retired.
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Old 12-10-2007, 06:59 AM   #6
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You can get a digital indoor/outdoor thermometer with probe with a 6 ft wire for about $10 at walmart, it will even record maximum and minimum temperatures for later recall.

They also sell completely wireless units, but these only update every 2-3 minutes though so the readings won't be instantaneous

You could probably make a simple sheet metal shroud for your exhaust manifold and then go to a junk yard and get an air cleaner, snorkel assembly with temp activated vacuum valve off a 1970-1980's car with a carb and rig up a system similar to the systems these vehicles came with. You would just need to T into a manifold vacuum hose on your car since the door that mixes hot air from around the manifold with cool outside air is operated by vacuum

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