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Aircon on effect tuning?

Specific discussion about the E89 2009 Z4 (sDrive35is, sDrive35i, sDrive30i, sDrive23i)
flybobbie
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Aircon on effect tuning?

Post by flybobbie » Mon Jun 21, 2021 6:26 pm

After discussion elsewhere on this board about switching ignition on for 10 seconds.
Did that few days ago i noticed the engine could rev with ease to 7000rpm and 60 in second.
Felt it could go past without too much effort. Not sure if there is a rev limiter.

Today had to go out for another replacement windshield and driving back the car seem to have more power.(Must windshield effect).
Then got home noticed i had left the aircon on low.
I wonder if the car tuning changes to compensate for aircon on?
Usually fans start to run, wonder if temperatures are different.
I noticed it running just below 120, not that warm today.

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Aircon on effect tuning?

Post by flybobbie » Mon Jun 21, 2021 7:24 pm

Could be more load on engine, engine getting hotter, running more optimum for the current ambient conditions.
I rarely see temp. just below 120 unless we have heatwave in traffic.
Temp. today about 14 c.

Pbondar

Aircon on effect tuning?

Post by Pbondar » Mon Jun 21, 2021 7:43 pm

What chassis /engine was this?

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Aircon on effect tuning?

Post by Rockhopper » Mon Jun 21, 2021 7:51 pm

Every car I’ve ever driven (including my Z4) runs much better with the AC off as it’s takes significant engine power to turn the compressor.

Pbondar

Aircon on effect tuning?

Post by Pbondar » Mon Jun 21, 2021 8:04 pm

So most stats state 10 ft lb ish and 10 bhp for non BMW engines..can't see why it would be much different for BMWs..

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Aircon on effect tuning?

Post by flybobbie » Mon Jun 21, 2021 8:14 pm

23i.

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Aircon on effect tuning?

Post by Pondrew » Mon Jun 21, 2021 8:18 pm

I don't think there is an "air con on" engine map TBH. The only thing it does do is increase the idle speed when you press the a/c button to stop the engine stalling at idle cos a ferkin great compressor is instantly drawing a big load, as well as a dirty great big electric fan being started at the same time.
I would check your cooling fan, or debris in the a/c condenser and oil cooler if it's running hot with the a/c on. I can't tell from just looking whether the a/c condenser is in front of the rad but that is normally the case on cars. If the fan isn't running on low speed, all the heat from the oil cooler, then a/c condenser will have to pass through the rad without forced assistance. A/c condensers kick out a lot of heat and can cycle on their HP switches without any warnings showing.
All good things come to those who wait. I'm really impatient which explains a lot.

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Aircon on effect tuning?

Post by Pondrew » Mon Jun 21, 2021 8:28 pm

Pbondar wrote: Mon Jun 21, 2021 8:04 pm So most stats state 10 ft lb ish and 10 bhp for non BMW engines..can't see why it would be much different for BMWs..
The old adage was "an a/c compressor uses 10% of engine power and uses 10% more fuel" but that was when an average ICE made 90bhp at 6000 rpm.
It's pertinent to remember that the compressor is directly driven off the crank belt. It will run at the same speed as the belt. They cycle constantly when driving, usually controlled by pressure switches for the refrigerant; LP and HP (this is all assuming there has not been a massive change in the technology of vehicle a/c compressors in the last 20 years, which I doubt).
All good things come to those who wait. I'm really impatient which explains a lot.

F31 320i. Good car.
E89 20i Now fully dried
Z3 'free litre'. Project and a half. Complicated!
Mazda3 sold
Tatty old R56 Mini Cooper. Money pit!

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Aircon on effect tuning?

Post by flybobbie » Mon Jun 21, 2021 11:27 pm

I will check all this week the effect of running with and without ac on low.

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Aircon on effect tuning?

Post by mcbutler » Tue Jun 22, 2021 10:28 am

Find a level stretch of road and set your 'instant fuel consumption' in the display.
Do a run with AC off and another with it on.
Then another turning it on half way through the run.
The amount of fuel it uses is surprising, especially when you first turn it on and its working hard to cool the car interior.

I rarely use it (tight northener) but I do switich it on once a month for a few minutes, this keeps the refrigerant and lubricant circulating and all the internal seals etc lubricated.
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Aircon on effect tuning?

Post by tomscott » Tue Jun 22, 2021 10:30 am

If you've got the top down there's no need for aircon :P

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Aircon on effect tuning?

Post by flybobbie » Tue Jun 22, 2021 11:37 am

tomscott wrote: Tue Jun 22, 2021 10:30 am If you've got the top down there's no need for aircon :P
Yes there is, if it's very warm nice to have cool breeze from the vents.

Just don't use it in winter to demist, did that once in a MR2.
Within seconds of switching off, the whole screen misted over, couldn't see out.

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Aircon on effect tuning?

Post by flybobbie » Tue Jun 22, 2021 11:40 am

mcbutler wrote: Tue Jun 22, 2021 10:28 am Find a level stretch of road and set your 'instant fuel consumption' in the display.
Do a run with AC off and another with it on.
Then another turning it on half way through the run.
The amount of fuel it uses is surprising, especially when you first turn it on and its working hard to cool the car interior.

I rarely use it (tight northener) but I do switich it on once a month for a few minutes, this keeps the refrigerant and lubricant circulating and all the internal seals etc lubricated.
My point in a way, the higher fuel consumption brings the engine temperature up to it's optimum.
Normally my daily 7 mile drive to work never gets it up to ideal running temp., aircon on might speed that up, then switch off.

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Aircon on effect tuning?

Post by mcbutler » Tue Jun 22, 2021 9:44 pm

flybobbie wrote: Tue Jun 22, 2021 11:40 am
mcbutler wrote: Tue Jun 22, 2021 10:28 am Find a level stretch of road and set your 'instant fuel consumption' in the display.
Do a run with AC off and another with it on.
Then another turning it on half way through the run.
The amount of fuel it uses is surprising, especially when you first turn it on and its working hard to cool the car interior.

I rarely use it (tight northener) but I do switich it on once a month for a few minutes, this keeps the refrigerant and lubricant circulating and all the internal seals etc lubricated.
My point in a way, the higher fuel consumption brings the engine temperature up to it's optimum.
Normally my daily 7 mile drive to work never gets it up to ideal running temp., aircon on might speed that up, then switch off.
I dont think it would make that much difference to be honest, best thing is to just try it I guess..
Mark
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Black leather

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Aircon on effect tuning?

Post by Pondrew » Tue Jun 22, 2021 10:12 pm

mcbutler wrote: Tue Jun 22, 2021 9:44 pm My point in a way, the higher fuel consumption brings the engine temperature up to it's optimum.
Normally my daily 7 mile drive to work never gets it up to ideal running temp., aircon on might speed that up, then switch off.
Let me get this right. You think that driving your 7 miles with the a/c on will help your engine? Seriously?
It will only put the engine under more load when it's cold and use more fuel.
There is a reason why BMW started fitting oil temp gauges instead of the normal water temp ones.
All good things come to those who wait. I'm really impatient which explains a lot.

F31 320i. Good car.
E89 20i Now fully dried
Z3 'free litre'. Project and a half. Complicated!
Mazda3 sold
Tatty old R56 Mini Cooper. Money pit!

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