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Old 07-23-2008, 03:32 AM   #1 (permalink)
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Subaru Outback Hot Air Intake Results

Had some free time tonight, decided to test a hot air intake as well as I could. Interesting results.

I did the test on the flattest straightest road in town, over a 1 mile stretch.

I sat cruise at 45 mph with the cruise control, then turned it back off with the brake pedal, resuming it with the resume switch. I used the scangauge II to do the reading. Reset it at a marker then read it each way.

Did a total of 12 runs, A-B-A-B-A-B Then with the variable changed.

The cold air intake was sucking air out of the fender well, while the hot air was sucking off the top of the intake manifold. This was done with an ultra high tech variable intake pipe. (Dryer hose)

Run with Cold:

1. 38.5
2. 36.5
3. 36.4
4. 37.1
5. 35.6
6. 36.0

Average: 36.68

Run with Hot:

1. 37.0
2. 36.8
3. 37.0
4. 34.8
5. 36.4
6. 35.1

Average: 36.18



A .5 mpg decrease overall at 45 mph. While this would be acceptable if there was another benefit, there isn't. The power is NOTICEABLY gone from the engine. With the hot air intake, its choked.

With the cold air coming in, the torque converter locks up quickly. It locks up way more than I'm used to, it can lock up in 4th and still climb a moderate hill at 45 mph without a problem.



Food for thought. Just thought I'd share my results, I encourage everyone to do their own testing.

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Old 07-23-2008, 05:25 AM   #2 (permalink)
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That mirrors my experience with hot air intakes on 3 different cars. It simply doesn't work.
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Old 07-23-2008, 06:31 AM   #3 (permalink)
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Its just a bunch of hot air...
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Old 07-23-2008, 09:20 AM   #4 (permalink)
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Do you know what the IAT was? My experience is when you get over about 115 it starts heading the wrong way on FE.
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Old 07-23-2008, 02:44 PM   #5 (permalink)
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Yup, I do.

Cold air intake was about 85~90 degrees, it'd dip as low as 75 which was about ambient too.

Hot air was about 150 degrees.
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Old 07-23-2008, 03:59 PM   #6 (permalink)
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and thats why they amke cold air intakes
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Old 07-23-2008, 04:19 PM   #7 (permalink)
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This is cosmic man!! Last wek i installed a rough and ready hot air intake to see how it works. I reversed the end of my intake to face the engine, then duct taped a length of flexible aluminium duct onto it and wedged the end behind the catalytic converter. I zip-tied a temp probe to the inlet hose just before the inlet manifold and wrapped it in some lagging to reduce the influence of the engine bay heat. Its hot in there! It seems i'm getting an inlet temp of 60 deg celsius but i'm dubious of the probe reading the heat off the inlet pipe. I'll drill a small hole and have it in the air stream and see if there is a difference.
Power is down but then fuel consumption should be down too. I'll see how this tank goes in a week or so. So far, its not worse. Fingers crossed.
I'd post pics only is damn ugly in the engine bay!

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Old 07-23-2008, 04:23 PM   #8 (permalink)
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Well, the troublesome think about intakes is that every car reacts differently to different temperatures. Some will pull timing with hot air, others won't.

I'm glad you did this test, but I hope others don't take this to mean that "hot air doesn't work" or that "hot air is debunked"
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Old 07-23-2008, 04:32 PM   #9 (permalink)
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There is also the consideration of intake length and flow. An ideal test would be with a pipe that can be re-oriented to hot or cold with the same length, number of bends and internal surface texture. Thanks for testing, though!
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Old 07-23-2008, 06:03 PM   #10 (permalink)
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I find HAI to work best on map sensor based cars. Works on the saturn and works well. We tested it multple times and fiddled with the IAT on nissan and it did NOT work at all. The only result was a serious power loss.

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