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      04-09-2013, 09:01 PM   #1
ZStig
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Better performance with AC on?

Floridian heat has sapped a butt dyno estimated 20hp from my car, compared to driving it in Philly. Whats odd, is that recently I've been driving it with the air conditioning on, and it feels like I have more torque.

The supercharger kit is very ambient temp sensitive with how the car feels. Its not decreasing in performance with time (heat soak), but feels stronger or weaker with as little as a 10* temperature variance.

I've heard some 911 turbos run faster with the AC on, because of how the AC lines are routed. Could it hold true for the Z4M also, or am I just being crazy?
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      04-09-2013, 09:59 PM   #2
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Sounds crazy but I've heard crazier, so you are probably normal.
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      04-09-2013, 10:04 PM   #3
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WTF? How does the AC have to be routed in order to actually have performance gain from using it?

We know that:
1) AC runs off of the crank, so it saps a tiny bit of power as-is when in use
2) AC generates heat with all else equal

Please enlighten me on the other variable(s)
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      04-09-2013, 10:10 PM   #4
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The ac compressor turns off during full throttle...
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      04-09-2013, 11:36 PM   #5
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MAGIC
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      04-09-2013, 11:38 PM   #6
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Quote:
Originally Posted by mfanatic325 View Post
WTF? How does the AC have to be routed in order to actually have performance gain from using it?

We know that:
1) AC runs off of the crank, so it saps a tiny bit of power as-is when in use
2) AC generates heat with all else equal

Please enlighten me on the other variable(s)
On the 911, the engine bay is very tight, and I imagine the cold AC lines might be near the intake manifold. Maybe I'm thinking of another car, but its something my mind recalled.

I've also always felt like the AC took away power, but maybe its helping the supercharger somehow. Very small chance, logically speaking, but I'll definitely try it on/off on my next dyno run
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      04-10-2013, 01:40 PM   #7
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AFAIK the AC compressor is belt driven and has a clutch, which closes when you turn your AC on, otherwise the pulley is free-wheeling. I doubt the lines running the refrigerant have any cooling effect on under-hood temps.

Last edited by yousefnjr; 04-10-2013 at 02:49 PM. Reason: Typo
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      04-10-2013, 02:19 PM   #8
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Quote:
Originally Posted by yousefnjr View Post
AKAIK the AC compressor is belt driven and has a clutch, which closes when you turn your AC on, otherwise the pulley is free-wheeling. I doubt the lines running the refrigerant have any cooling effect on under-hood temps.
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      04-10-2013, 03:18 PM   #9
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Quote:
Originally Posted by yousefnjr View Post
I doubt the lines running the refrigerant have any cooling effect on under-hood temps.
The lines only get cold after the expansion valve/evaporator (which is located in the cabin heating unit). Before that they are ambient.
Only the lines after the evaporator might be coldish. The evaporator tries to absorb as much heat as possible though.
Everything else is hot in the ac system, and judging form the size of the average condensor there's a fair amount of heat to be dissipated (and gets both under the hood and directly heats the radiator (which is usually placed behind the condensor).

I think the only better performance with ac on is coming from the driver who can keep a cool head
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      04-10-2013, 03:29 PM   #10
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Maybe gas without ethanol? I've seen mileage increases in other cars after leaving Florida, not sure if there are performance increases too.
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      04-10-2013, 04:16 PM   #11
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Quote:
Originally Posted by GuidoK View Post
The lines only get cold after the expansion valve/evaporator (which is located in the cabin heating unit). Before that they are ambient.
Only the lines after the evaporator might be coldish. The evaporator tries to absorb as much heat as possible though.
Everything else is hot in the ac system, and judging form the size of the average condensor there's a fair amount of heat to be dissipated (and gets both under the hood and directly heats the radiator (which is usually placed behind the condensor).
Thanks for breaking it down for me, my mind must be playing tricks on me
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      04-10-2013, 06:24 PM   #12
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I route the AC back to the intake
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      04-11-2013, 09:18 PM   #13
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Quote:
Originally Posted by DSC_OFF View Post
I route the AC back to the intake
sweeeet
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      04-11-2013, 09:22 PM   #14
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Quote:
Originally Posted by DSC_OFF View Post
I route the AC back to the intake
really. ? i want to see it.
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      05-29-2013, 07:59 PM   #15
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I noticed a modest boost in highway MPG with the a/c on in 50-60 degree evening temps. Looking to repeat the experiment in 90 degree daytime heat. Also, my thermostat (gauge on dash) reads low around 180 when full warm... Maybe some correlation.
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      06-11-2013, 06:45 PM   #16
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Quote:
Originally Posted by ZStig View Post
MAGIC
I liked that way too much.
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      06-11-2013, 08:04 PM   #17
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Quote:
Originally Posted by Punko View Post
I liked that way too much.
Its funny re-reading it for me now
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      06-11-2013, 09:07 PM   #18
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I'm sure it was entertaining for everyone
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      06-12-2013, 12:16 AM   #19
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I notice that my exhaust note sounds a lot better with the air on.
(Because it's working harder to run the compressor)

Maybe it just sounds torquier with the air on.
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      06-13-2013, 03:04 PM   #20
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Go to the dyno!

Maybe the added load% remaps fuel/vanos to a diffrent map?
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      06-15-2013, 05:07 AM   #21
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Ac steals power. when I dynoed my m it was only like 2hp difference but still a loss.
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      06-15-2013, 10:02 AM   #22
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Quote:
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Ac steals power. when I dynoed my m it was only like 2hp difference but still a loss.
thanks for the confirmation
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