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Old 07-24-2006, 01:23 AM   #51
nhluhr
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Quote:
Originally Posted by CynicX
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).
I would hazard a guess that those SP's using the AC instead of windows are also going to have less hearing loss and also be more comfortable/presentable from not sweating on the hotter days.
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Old 07-24-2006, 11:25 AM   #52
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Quote:
Originally Posted by ElementalFiend
I'm driving an '06 2.5i and there isn't much of a difference.
I have a 2.5i too and I dont notice much of a difference. My friend's Mini Cooper S has a huge difference starting from stop with AC or without. Could NA vs FI make a difference?
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Old 07-24-2006, 11:52 AM   #53
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Quote:
Originally Posted by REX8
its a huge difference...actually have to shift faster the revs fall off so quick....

+1.......


.......I can't stand driving with my AC on. Tust me, with temps hitting tripple digits on a daily basis, and humidity levels way over eleventy billion %, I would be using it if there was no difference.

Last edited by licwyd7755; 07-24-2006 at 11:58 AM.
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Old 07-24-2006, 12:10 PM   #54
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Quote:
Originally Posted by Subie Gal
huh?

under WOT the AC shuts off....

i have AC in my race car, and run with it on each and every race.

*shrug*

to each their own i guess but i have not noticed any power loss.

Jamie
It does shut off at WOT, but evertime I change gears it clicks back on and the revs drop too quickly and it makes the revs too low for the next gear unless I really force the shifter into the gate. What about if you are at part throttle in a race, it definitely makes the throttle more dull and not as responsive? I guuess you've just gotten used to it, or it doesn't make as big a difference on the dirt.
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Old 07-24-2006, 01:30 PM   #55
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Quote:
Originally Posted by 8Complex
Having AC on in my car makes it go faster. True story.
Mine too! It's still not as fast as an SRT-4 with the A/C on......
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Old 07-24-2006, 01:44 PM   #56
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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
That's interesting. I'm sure every make and model has a different break even point (if there is a break even point). A more aerodynamic vehicle will likely have a lower break even point than a less aerodynamic one, and a vehicle with a larger engine will expend a much lower percentage of its power on AC than a smaller car, thus the impact will be a lot less obvious. A Pruis, for example, is probably much more effiecent with AC on than with the windows down at 50mph. I don't know why they would have choosen the worst vehicle to run their test on rather than the best, or at least a more typical, vehicle (unless of course they set it up so they could "bust" the myth).
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Old 07-24-2006, 04:09 PM   #57
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The second radiator fan goes on with the AC switch. Hence, the mod to keep the AC from going on, yet turn on the second fan, can increase performance under some circumstances. This was described on Nasioc a long time ago.
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Old 07-24-2006, 04:13 PM   #58
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On a positive note, once I installed my stealthback and picked up 15 or so hp, the power suck from a/c isn't noticable. I still hardly ever use it, but it helps.
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Old 07-24-2006, 04:20 PM   #59
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Quote:
Originally Posted by 8Complex
Having AC on in my car makes it go faster. True story.

yah man, i pump ac into my intercool4r and through my vents, real fast if you ask me..especially at wot cuz it teh shuts down my interior vents and just blows cold air at my intercoolr, god i love this ^ mount setup
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Old 07-24-2006, 04:36 PM   #60
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It's a very noticeable difference between AC on and off at part throttle in a 2.0L WRX. I turn mine off momentarily when getting ready to start from lights and stop signs because it bogs the motor down so much that it's hard to start smoothly. And trying to get the revs up off idle for hill starting with the A/C on takes a ton more throttle than with the AC off.

It may switch off at full throttle, but it's definitely like dragging around a boat anchor in normal driving with small throttle openings.

Last edited by Chuck H; 07-24-2006 at 04:42 PM.
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Old 07-24-2006, 04:50 PM   #61
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Any small displacement engine without a lot of low end torque is going to be affected by the presence of an A/C compressor turbo or not. I find that double clutching helps a bit to get rid of some of the drivetrain slack induced by the laggy engine, but it's rare that I use A/C as the heat doesn't bother me.
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Old 07-24-2006, 05:31 PM   #62
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Quote:
Originally Posted by Subie Gal
subaru's AC system shut off under WOT ... period.

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

Jamie

Out of curiosity, when did they start this?

I thought I noticed it in my '91 LT, but that may just be something else. It didn't seem to shut off in my '94 wagon, but it was so slow that I probably just didn't notice.

I knew WRXes did, but I just didn't know what all else they did it in.....
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Old 07-24-2006, 05:40 PM   #63
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It is harder to notice the difference when driving an auto with the air on. With the air on, driving stick, it is more easily noticed, you have to work the clutch/gas a bit differently.
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Old 07-24-2006, 05:44 PM   #64
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I try to go w/o using AC whenver possible. It is more strain on everything from the engine to the cooling system. Although it is not too bad on our cars, it can use up to a third of a vehicle's gas just to run the AC. Regrding auto-shutoff and WOT, it is a cool feature, but it still sucks when trying to just get on it a little. If I am getting on the freeway I just turn it to 'vent' temporarily or push the AC button to turn it off during the WOTness. It's not the fans that are teh suck, it is running the AC compressor.

It is a good idea; however, to run it for a few minutes at least once a month to maintiain the seals/lubricate stuff.

So ya'll know, I've found that at speeds above 55ish, I get the best best balance of circulation and tolerable noise from rolling down just the 2 passenger side windows about 3-4 inches.
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Old 07-24-2006, 05:48 PM   #65
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Quote:
Originally Posted by nhluhr
I would hazard a guess that those SP's using the AC instead of windows are also going to have less hearing loss and also be more comfortable/presentable from not sweating on the hotter days.
MythBusters did the same test with an SUV @ about 50-55 mph and the windows car won. I guess it would depend on the speed of the vehicle and how much it relies on aero for it fuel economy. An SUV is not taking nearly as much of a aerodynamic hit as say a modern Legacy with the windows down. Also, the effects of drag increase significantly as speed increases.

So, if yur just puttin' around, go windows. But if you were cruising on the freeway and basically keeping a constant speed, use AC.
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Old 07-24-2006, 05:54 PM   #66
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Quote:
Originally Posted by shemoves
Also, the effects of drag increase significantly as speed increases.
I have previously calculated the amount of power consumed solely by wind drag on the 2004 STi. It basically works out that any speed above about 40mph, it is better to have the windows rolled up.
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Old 07-24-2006, 06:17 PM   #67
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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
Uh, the car gets better mileage w/ ac OFF, because the AC isn't using any POWER when it's off.

EVERY FEATURE, from hazards to headlights, requires POWER to use. Period. You can't make freezing cold air without P O W E R.


I am not denying the car cuts ac load at WOT. It does.


WHY do you think that's so? BECAUSE THERE IS A POWER LOSS. (Duh.)

If there were NO LOSS, there would be NO NEED to cut the AC at WOT.

Ponder that for a second.

ALSO: You are not running at WOT every time you hit the gas (well, maybe you are, but not most folks). Off the line, do you run at WOT? I have yet to meet someone who launches at WOT very well.

Here's another test: Go to the drag strip and do four runs: Two w/ ac, and two without. Guess what? You'll run much faster without AC. IN ANY CAR.

FINALLY: Datalog a stock REX in 90+ degree weather with A) AC off and B) AC on under heavy load. Guess which exhibits more detonation? AC on.

It's funny to see someone as knowledgeable as yourself talk down to others when you have no apparent knowledge of the physics of how a vehicle's AC works either. Just because a car cuts AC at WOT does NOT mean you should push its limits with the AC on.

As I said before, IT CUTS AC FOR A REASON: To prevent the H U G E current demand of your AC system.


Every action has an equal and opposite reaction. Compressing and cooling warm air requires POWER. Period. Try to run your ac with no alternator. It won't work too well. It's why they run those red and black wires to all of the gizmos in your Subie...they require power.

Saab-on-the-Cobb
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Old 07-24-2006, 11:16 PM   #68
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I don't know. In my 94 4runner turning off the AC is like turning on a turbo. I hardly ever use it.
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Old 07-25-2006, 12:04 AM   #69
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All you people need to get a life. 3 pages on power loss w/ the AC on.
Jesus Christ you should all be driving 20 year old Hyundais.
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Old 07-25-2006, 08:49 AM   #70
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Quote:
Originally Posted by PRS82F
All you people need to get a life. 3 pages on power loss w/ the AC on.
Jesus Christ you should all be driving 20 year old Hyundais.
There is no such thing as a 20 year old Hyundai.
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Old 07-25-2006, 09:01 AM   #71
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Quote:
Originally Posted by PRS82F
All you people need to get a life. 3 pages on power loss w/ the AC on.
Jesus Christ you should all be driving 20 year old Hyundais.
You were darn close to making it 4 pages...
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Old 07-25-2006, 09:08 AM   #72
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i dont see any lose of power in my car.
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Old 07-25-2006, 10:07 AM   #73
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Its not a signifigant loss in power, but enough to make honda drivers notice
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Old 07-25-2006, 10:16 AM   #74
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Of course the AC reduces power; that's basic thermodynamics and there is no way around it.

Quote:
Originally Posted by Chuck H
It's a very noticeable difference between AC on and off at part throttle in a 2.0L WRX. I turn mine off momentarily when getting ready to start from lights and stop signs because it bogs the motor down so much that it's hard to start smoothly. And trying to get the revs up off idle for hill starting with the A/C on takes a ton more throttle than with the AC off.

It may switch off at full throttle, but it's definitely like dragging around a boat anchor in normal driving with small throttle openings.
I do the same thing, and also when climbing hills on the highway.
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Old 07-25-2006, 10:32 AM   #75
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Another good way to think about it for the doubters. We all realize that A/C probably only drains 10 or so hp. That doesn't sound like much on a 227 hp car. But look at any dyno of a stock, or even modified WRX. Down around 2000 RPM, they're only making 50 hp or less. Losing 10 of those to the A/C compressor is pretty significant.
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