aircon vs full throttle

[repenttokyo]

It's a standard feature on Crown Victoria police cars. Full throttle = air con cutout.

[BMWDriver]

I think torque is more at cause here. The a/c gives resistance to the motor, and the engine translates the power in torque to counter that resistance. Past a certain RPM, torque is sufficiently high to free up the power of the engine and drive the a/c comfortably. But mileage will suffer a bit.

This will not answer the question though, but it would not surprise me if the a/c was not turned off.

The M50 is pretty slow to start in low revs because the torque is too low there. That engine really wakes up above 3000 rpms, I find.

[Jan]

I had my 540 touring on a dyno today. I had it measured 2 times, with and without the aircon on. With the aircon on, it has about 10hp lower fro 1000 to about 3500rpm and after that it has the same as with out the aircon on.

Does anyone know if it shuts off the aircon pump at full throttle at around 3500 rpm, it seems like it.......

[525iZA]

My parents had a '99 Mercedes E240.

That V6 loved to rev right up to the red line and when you floored it to overtake cars on the high way, you got that funny smell when the A/C has just been switched off... So yes, in that Merc a/c was switched off under full acceleration.

Could probably also be the case with your BMW!

[healtoeit]

My butt dyno tells me that! With the ac on my 525i is sooo slow! I turn it off to accelerate from a stop then turn it on for cruising.

Side note: the e39 540i ac compressor stays on all the time... their is no way to turn it off w/o disconnecting it

[Tiger]

AC has a speed sensor. If it senses a sudden acceleration or high sterss situation, AC will shut off. And yes, this is normal to see AC suck away the extra power.

[Tiger]

No... this means something is wrong with your AC system.

[repenttokyo]

how are they correcting the dyno reading to give you the numbers at the crank? because obviously, it's not 285 at the wheels.

[repenttokyo]

During deacceleration, it measures the loss in trans etc. and then add that to the reading, to give crank hp and torque.


interesting - cool system.

[Jan]

Here are the 2 dyno runs, the highets numbers are from the run with the aircon on.
It´s a stock 540 with about 270.000km

http://www.bmwe30.dk/rulning540.jpg

[RallyD]

my 525i does not turn the compressor clutch off during WOT,
every other car I have owned did shut down the compressor.

Its more about luxury than being the first one there, i guess.

[pingu]

Eh? The a/c gives, in effect, some extra friction to the engine. The torque (i.e. energy) that gets used up in overcoming this a/c friction can't be used to drive the dyno and thus won't be measured by the dyno. Or did you mean something else?

[pingu]

That's so impressive I want to make sure I've not missed something:

- the 540 M60 is spec'd at 286 bhp.

- and a 540 with 270,000km (about 160,000 miles) still manages to achieve about 286 bhp?

Impressive - and good to know!

[Jan]

That's so impressive I want to make sure I've not missed something:

- the 540 M60 is spec'd at 286 bhp.

- and a 540 with 270,000km (about 160,000 miles) still manages to achieve about 286 bhp?

Impressive - and good to know!

You have not missed anything;)

This is my second 540 and the other one as dynoed at 285,1hp and 398nm, with about 250.000km.

[Jan]

how are they correcting the dyno reading to give you the numbers at the crank? because obviously, it's not 285 at the wheels.

During deacceleration, it measures the loss in trans etc. and then add that to the reading, to give crank hp and torque.

[genphreak]

Eh? The a/c gives, in effect, some extra friction to the engine. The torque (i.e. energy) that gets used up in overcoming this a/c friction can't be used to drive the dyno and thus won't be measured by the dyno. Or did you mean something else?... FW(L)IK.... the ECU shuts down the AC when it so chooses... and on the Motronic 1.3, I am sure this means near and at WOT only.

[pingu]

Did you done anything (e.g. cleaning up the intake manifold) to the engines other than just routine replacement of oil/filters?

My car has had no major work other than routine stuff (oil, filters, thrust arm bushes etc). Those figures are so impressive I just want to make sure that they would apply to me!

Thanks!

[Ross]

I don't think so. Many cars, especially little wheezers like the 525 shut off the a/c compressor under large loads. I'm not sur what determines when but would guess it's tied to the vacuum signal.

[Guapo]

I don't think so. Many cars, especially little wheezers like the 525 shut off the a/c compressor under large loads. I'm not sur what determines when but would guess it's tied to the vacuum signal.

I'd be more inclined to think it'd work off throttle position sensor voltage. I don't know about the BMW, but my 300ZXTT does shut off the compressor at WOT.

[Jan]

Did you done anything (e.g. cleaning up the intake manifold) to the engines other than just routine replacement of oil/filters?

My car has had no major work other than routine stuff (oil, filters, thrust arm bushes etc). Those figures are so impressive I just want to make sure that they would apply to me!

Thanks!

I am working on a new M62/S62 engine, so I just do routine replacements on the engine in the car.

[Jon K]

I don't think so. Many cars, especially little wheezers like the 525 shut off the a/c compressor under large loads. I'm not sur what determines when but would guess it's tied to the vacuum signal.

TPS and MAF flow