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Android Users - Coming Soon! - Migrating from aCar 4.8 to 5.0

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Old 09-26-2008, 03:48 PM   #31
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Originally Posted by theholycow View Post
That heat-scavenging effect maybe also increases efficiency after warmup -- instead of discarding that heat energy, it's put back into the engine. Additionally, the warmer air may enhance fuel vaporization.

There could also be other factors at work for your high-altitude observations -- for example, the lower pressure air outside the engine would increase pumping losses effectively nullifying the WAI's density advantage. Hills could cause you to drive less efficiently, climate might require the fan to be used a lot, etc
I can almost buy most of these arguments, but not quite... Maybe it's just because I'm coming from a skeptical point of view.

The heat aiding vaporization probably works in a physics classroom, but this weekend, why don't you go for a drive, then open your hood and put your hand on your intake manifold or the side of your cylinder head when you stop. I'm going to go out on a limb and say those parts will be too hot to touch (the head especially). They add enough heat to the air to vaporize the fuel and then some by the time the fuel hits the back of the valves, and if there is any unvaporized fuel at that point, the valves will be hot enough to finish the job for sure. An extra 30 degrees of IAT isn't going to make or break that equation, especially on an engine with throttle body injection where the fuel has a relatively long time to vaporize before it enters the CC.

Recycling heat energy? The percentage of heat energy in the intake air compared to what the engine producing is probably to infinitesimal to measure.

Lower barometric pressure? Nope, that's a zero sum equation as far as I can tell. Keep in mind that the air pressure is lower on both sides of the engine (intake and exhaust that is), so any differences in the amount of energy necessary to pull the air in would be nullified by the lower amount of energy needed to force the air back out.
The only thing I can say about this one is that less dense air will reduce your dynamic compression. That'll translate to lower FE every time I think.

Is anybody on this forum a pilot? I'm guessing that pilots can teach us a thing or two about altitude and FE....
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Old 09-26-2008, 03:55 PM   #32
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Hal, keep in mind a pump works off of differences in pressures from it's outlet to it's inlet. On an engine, this is from the intake tract to the compression stroke of a 4 cylinder engine. The compression is the same, but the difference in pressure is less the higher the altitude you go, and the engine has to work harder for the same amount of air movement.
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Old 09-26-2008, 04:01 PM   #33
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how did this spam thread turn into a full blown discussion about the WAI vs CAI.
Don't blame me, I tried to make it about avian genitalia.
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Old 09-30-2008, 11:43 AM   #34
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Hal, keep in mind a pump works off of differences in pressures from it's outlet to it's inlet. On an engine, this is from the intake tract to the compression stroke of a 4 cylinder engine. The compression is the same, but the difference in pressure is less the higher the altitude you go, and the engine has to work harder for the same amount of air movement.
This effect will be the same no matter if the air density decrease is caused by altitude or temp. Increasing temp will attenuate the effect somewhat, but to overcome the decrease in efficiency caused by air density, the positive effect of temp alone would have to be substantial to say the least. The 6K ft elevation change that I'm used equates to a roughly 15-20% (depending on who's numbers you believe) change in air density. That usually changes my MPG by about 3 mpg on my 20 mpg=/- Ranger.

If memory serves me correctly (from my turbocharger design calcs) the effect of air temp on density is more substantial than altitude by a fair margin. So you'd need to overcome some pretty substantial losses before you saw any gains at all. I just can't find any proof that's the case. It's easier for me to believe that people with WAI's live in cooler climates and are seeing gains during warmup averaged over short drives.

Does anybody with a WAI live in the southwest or do nothing but highway driving? I'd love to see those fuel logs? Have Semi drivers switched over to WAI's I still the external air filter intakes on lots of the rigs I see on the highway, and those guys go to great lengths to save on gas.
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Old 09-30-2008, 12:13 PM   #35
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I've seen a very modest gain on my truck, but my IA really doesn't start to rise until the thermostat opens up. I'm thinking about some ducting to suck air from around the manifold.

-Jay
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Old 09-30-2008, 12:33 PM   #36
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that is what I did. I am still getting air from under my bumper (which is good because I don't overheat). this causes my temps under the hood to be low so I set up a WAI with a heat shield to deflect the cool air away from the intake. take a look at my pics.

$10 bucks and a little time will prove/disprove the theory behind it...if anyone was having issues with whether it worked or not. there are several DIY threads on the WAI.
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Old 09-30-2008, 12:40 PM   #37
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Hal9000: Intake Air temp works much different on a Diesel than a gas engine. They dont have to maintain a specific air/fuel ratio to operate.
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