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Old 07-23-2006, 08:55 PM   #26
flyboymike
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Quote:
Originally Posted by 04_wagon
even when i was parked after cooling the intercooler off with ice and leaving the hood open?
That can help reduce heat soak, which will help you with thermodynamic efficiency of the engine because you cool the air down after it gets compressed. However, the higher heat outside still means you'll have lower density air coming in, translating to fewer air molecules, even when you put it through the compressor. Less air molecules = less power.
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Old 07-23-2006, 08:55 PM   #27
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Quote:
Originally Posted by 575rider
extremely common in all cars, especially 4 cylinders, be happy there's a turbo there in a normally aspirated 2.0 4 cylinder you'd REALLY feel it. You don't have a thing to worry about.
I'm driving an '06 2.5i and there isn't much of a difference.
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Old 07-23-2006, 08:59 PM   #28
Subie Gal
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Quote:
Originally Posted by DrD
while that is indeed true, in daily driving most of us don't drive with the pedal to the floor all the time...

oh sorry that would be me....
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Old 07-23-2006, 09:12 PM   #29
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yes, the AC shuts off at WOT... but unless you leave ever stoplight at WOT, it WILL make a fairly large difference. btw, most belt/pulley systems are rated at around 10hp max, so you could lose up to 10hp at the crank.
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Old 07-23-2006, 09:20 PM   #30
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Quote:
Originally Posted by Subie Gal
we're not talking about GAS MILEAGE

we're talking about POWER
and...

subaru's AC system shut off under WOT ... period.

so if you need power, you get it....


this has been covered a 100gazillion times...

Jamie
We are not talking about either anymore. We're talking about nothing. Thread should have died long ago.
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Old 07-23-2006, 10:13 PM   #31
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Unless he runs full throttle from red light to red light, the AC will be affecting performance: Or rather, affecting FEEL. My daily driver feels like a it's powered by a hair dryer at partial throttle (such as in traffic). I sometimes turn the A/C off when starting from a stop in the 92x, recycling the cool air until I'm into about 3rd gear.... just a thought.

P.S. Real race cars have no doors or windows... let alone AC
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Old 07-23-2006, 10:16 PM   #32
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Quote:
Originally Posted by Subie Gal
what a load of crap

my car dyno's at 205hp at the WHEELS
my car is GT aka STOCK class

and those of you who say AC kills power, dont know much about the Subaru AC system....

Jamie
It kills a lot of power in part-throttle driving. I also thought it was RPM dependent too. So WOT at 2k wouldn't shut it off...

Could be wrong...in daily driving though, its a huge difference...actually have to shift faster the revs fall off so quick....

Sometimes I even make the joke with the A/C on, youu have to Double clutch your upshifts...
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Old 07-23-2006, 10:31 PM   #33
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AC compressor is not that heavy to turn. In fact, during freeway driving. You'll lose more power having the windows down then AC on.

Few condition will force ECU to shut down AC. when your TPS reading higher then 4 volts, your speed under 15 MPH and your engine coolant temp reachs over 215 F. There is also a valve and sensors for the R134A and outside temp to pervent AC freeze up, or blow up due to high pressure.
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Old 07-23-2006, 10:32 PM   #34
FreNetiC WRX
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yes, and the myth that you lose gas, is in fact a myth. the only thing you lose (as you have found out) is power...
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Old 07-23-2006, 10:35 PM   #35
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Quote:
Originally Posted by FreNetiC WRX
yes, and the myth that you lose gas, is in fact a myth. the only thing you lose (as you have found out) is power...
Thats certainly not a myth.

Surely you are not saying that your gas mileage doesn't fall with your A/C on. Of course it does...the compressor isn't turning itself....
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Old 07-23-2006, 10:36 PM   #36
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Quote:
Originally Posted by Nismo
You'll lose more power having the windows down then AC on.
You don't loss power with the windows down, you gain drag.
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Old 07-23-2006, 10:37 PM   #37
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Quote:
Originally Posted by aerostar
Actually they did a test on Mythbusters, one of my favorite shows. What was interesting was that at 50 MPH the truck with the windows down went around 20-25 more miles than the truck that had the windows up with the A/C on. oO
I think you need to rewatch that episode because you have that backwards.
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Old 07-23-2006, 10:38 PM   #38
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Quote:
Originally Posted by Smoby
I think you need to rewatch that episode because you have that backwards.
No, he got it right.

The truck with the windows DOWN got better mileage (traveled further) than the one with the A/C on...
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Old 07-23-2006, 10:43 PM   #39
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Quote:
Originally Posted by REX8
No, he got it right.

The truck with the windows DOWN got better mileage (traveled further) than the one with the A/C on...
that is correct.

http://kwc.org/mythbusters/2004/11/m..._catapult.html


Quote:
"Urban puzzle": it is more efficient, on a hot day, to run with the A/C on and windows up than to run with windows down (b/c of increasing car's drag).

Computer-based mpg measurements:

11.7/11.8 with A/C on and windows up
11.7/11.8 with A/C off and windows up
11.3 with A/C off and windows down
So, according to the computer, it's better to use A/C with windows up.

This was too quick and easy for TV, so they decided to stage a seven hour marathon, race-til-you're-empty duel, with Jamie driving an SUV with A/C on and Adam driving an SUV with windows down. Though, once the safety inspector intervened, it was no longer a seven-hour marathon, it was a bit slower (45mph instead of 55mph), and a lot shorter (only 5 gallons each).

Jamie's A/C car ran out of gas first -- Adam's windows down SUV ran for another 30 laps -- completely contradicting the computer mpg estimate. Computer estimate based on air flow into the engine, so it would appear that it is unable to properly model the difference between A/C and windows down.
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Old 07-23-2006, 11:39 PM   #40
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Quote:
Originally Posted by Subie Gal
what a load of crap

my car dyno's at 205hp at the WHEELS
my car is GT aka STOCK class

and those of you who say AC kills power, dont know much about the Subaru AC system....

Jamie
that's true... I always laugh when people turned their AC off when their pushing the car... LOL...
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Old 07-23-2006, 11:48 PM   #41
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Consumer Reports independently confirmed the same thing as Mythbusters. Windows down is better for gas mileage than using AC
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Old 07-24-2006, 12:38 AM   #42
Nismo
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It all depends what your talking about. If they didn't use cruse control then that means it's all base on STFT instead of LTFT. Which is base on driver really. I had to go to Ont from Irvine which is about 100 miles round trip. FOR ME, I get more mileage with windows up AC on, then windows down. Looks like more testing need to be done. LOL
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Old 07-24-2006, 12:48 AM   #43
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ok need to close this cause people are getting away from the point. it was why was their power loss during acceleration. not will i get better gas milage
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Old 07-24-2006, 12:58 AM   #44
BajaGreg
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Default hit the road b*tch!

I once had a girl in my car who said it was too cold with the A/C on.
She rolled her window all the way down. It was 111 degrees outside.
She wouldn't close her window. So I pulled over and kicked her *ss out of the car!
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Old 07-24-2006, 01:01 AM   #45
nhluhr
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The standard impreza A/C system is rated 17,400BTU/hr (5.1kW) cooling at full load. That is roughly 6.8hp. So you know that it consumes quite a lot more than that just because of efficiency losses of the compressor, etc.
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Old 07-24-2006, 01:01 AM   #46
Nismo
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Quote:
Originally Posted by 04_wagon
ok need to close this cause people are getting away from the point. it was why was their power loss during acceleration. not will i get better gas milage

oh sorry!!

It is a fact you'll lose power when you turn the AC on since it's DRIVEN by the belt which is turned by crankshaft. There for, YES AC = less power
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Old 07-24-2006, 01:10 AM   #47
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with temps at an average of 100+ these past couple days here in sac, id gladly lose some mileage for a lot more comfortable driving.
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Old 07-24-2006, 01:10 AM   #48
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Having AC on in my car makes it go faster. True story.
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Old 07-24-2006, 01:19 AM   #49
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Quote:
Originally Posted by 8Complex
Having AC on in my car makes it go faster. True story.
Nice response...
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Old 07-24-2006, 01:21 AM   #50
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Its ashame Mythbusters didnt use an areodynamic vehicle. Instead they used SUV's, at least the episode I saw.

Of course the vehicle with the windows down got better MPG at high speeds. The thing didnt have areodymanics to begin with. Generally the difference in city/highway MPG is alot less of a difference on larger none areodymanic vehicles. Like a Jeep may get 16/19 while a car will get 22/30.

The Maryland State Police posted a report that the highway pratrol man get better MPG using the A/C vs having the windows down (anything to save a dime I guess).

/end off-topic rant....
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