[BarryJI]

Once upon a time, before a few of you were born, I had another turbocharged four-banger, a Lotus Elan. I loved it but, in the time-honored tradition of Lotus Cars, every component that was not part of the drivetrain was licensed from another manufacturer, so this little two-seater had an air conditioning unit shoehorned into it from some great big boat of a Chrysler. Lotus only provided a/c reluctantly, to appease the American marketplace, and were therefore probably not at all surprised when, upon switching the a/c on, this otherwise lively little sports car suddenly had all the torque of an electric lawn mower. So, despite living in southern California, I never once used the a/c; thank goodness the car was a convertible.

The 228i M Sport is the first four-cylinder turbo I've had since then. So far, I've noticed that the effect of a/c (not turned all the way up, or even close) seems pretty minimal in normal traffic conditions (but it certainly eats into fuel consumption). I am wondering, especially as I am going to get a Stage 1 tune tomorrow, just how much effect a/c has on power output, both HP and torque. Can anyone quantify this, even in approximate terms?

[Sportstick]

Originally Posted by BarryJI

Once upon a time, before a few of you were born, I had another turbocharged four-banger, a Lotus Elan. I loved it but, in the time-honored tradition of Lotus Cars, every component that was not part of the drivetrain was licensed from another manufacturer, so this little two-seater had an air conditioning unit shoehorned into it from some great big boat of a Chrysler. Lotus only provided a/c reluctantly, to appease the American marketplace, and were therefore probably not at all surprised when, upon switching the a/c on, this otherwise lively little sports car suddenly had all the torque of an electric lawn mower. So, despite living in southern California, I never once used the a/c; thank goodness the car was a convertible.

The 228i M Sport is the first four-cylinder turbo I've had since then. So far, I've noticed that the effect of a/c (not turned all the way up, or even close) seems pretty minimal in normal traffic conditions (but it certainly eats into fuel consumption). I am wondering, especially as I am going to get a Stage 1 tune tomorrow, just how much effect a/c has on power output, both HP and torque. Can anyone quantify this, even in approximate terms?

I don't have numbers, but my understanding is that the effect is less than the aerodynamic drag loss of lowering the windows.

[BarryJI]

Originally Posted by Sportstick

I don't have numbers, but my understanding is that the effect is less than the aerodynamic drag loss of lowering the windows.

I wish...but I am dubious about this equation.

[Sportstick]

Originally Posted by BarryJI

I wish...but I am dubious about this equation.

Maybe this helps a small bit? Not BMW-specific and fuel efficiency is a surrogate for power drain but the overall analysis seems rational.

https://blog.gasbuddy.com/posts/The-...57041-563.aspx

[abp689]

Originally Posted by BarryJI

I wish...but I am dubious about this equation.

Reference Mythbusters.

[jbenington86]

IMO the A/C system in every BMW I have owned sounds and feels like it pulls more power than any other vehicle I have owned....My 128i (manual) almost stalled due to A/C power pull when coming to a stoplight at the end of a 5 hour road trip the cause was the A/C. Once I turned it off the car was normal again. I have never had any problems like this in my wifes 370z. Also the amount of power being pulled completely changes how the clutch feels and make it much more difficult to shift. In my wifes 370z no problems at all no matter how low I have the temp.

If it is one thing BMW is not good at.... it is making a poorly designed A/C system

[aerostar]

Originally Posted by jbenington86

IMO the A/C system in every BMW I have owned sounds and feels like it pulls more power than any other vehicle I have owned....My 128i (manual) almost stalled due to A/C power pull when coming to a stoplight at the end of a 5 hour road trip the cause was the A/C. Once I turned it off the car was normal again. I have never had any problems like this in my wifes 370z. Also the amount of power being pulled completely changes how the clutch feels and make it much more difficult to shift. In my wifes 370z no problems at all no matter how low I have the temp.

If it is one thing BMW is not good at.... it is making a poorly designed A/C system

I can't believe you guys are complaining about the A/C in the BMW...

I just came from a WRX and when the A/C was on the RPM between shifts w/ clutch in would drop like a rock.

I love the A/C in this car.

[jbenington86]

Originally Posted by aerostar

I can't believe you guys are complaining about the A/C in the BMW...

I just came from a WRX and when the A/C was on the RPM between shifts w/ clutch in would drop like a rock.

I love the A/C in this car.

Like you WRX the rpms on my 128i would have a significant drop. The engine rpms would go below 500 and the car would shake but the computer would finally kick in and give it extra fuel bringing it back to a normal idle.

Not saying the A/C itself is bad because it keeps everything really cool in the cabin but it draws significantly more power than any other car I have driven.

In my wifes 370z I could have the A/C on the coldest setting with the fan blasting and not even notice anything different in the feel of the engine, clutch engagement or shifting.

[aerostar]

Originally Posted by jbenington86

Like you WRX the rpms on my 128i would have a significant drop. The engine rpms would go below 500 and the car would shake but the computer would finally kick in and give it extra fuel bringing it back to a normal idle.

Not saying the A/C itself is bad because it keeps everything really cool in the cabin but it draws significantly more power than any other car I have driven.

In my wifes 370z I could have the A/C on the coldest setting with the fan blasting and not even notice anything different in the feel of the engine, clutch engagement or shifting.

No I mean if I rev'd to 3k RPM, shifted to 2nd or whatever next gear, the RPM would drop like a rock and I'd have to clutch in clutch out as fast as I could to make it on time.

[jbenington86]

Originally Posted by aerostar

No I mean if I rev'd to 3k RPM, shifted to 2nd or whatever next gear, the RPM would drop like a rock and I'd have to clutch in clutch out as fast as I could to make it on time.

Same here. Quicker shifting is required on my 128i. My M235i I don't notice it much since it is an auto but I can feel a similar power drain with the A/C on.

[Merc for hire]

In my manual 228i, I can definitely feel the faster engine speed drop between gear changes.

I kinda like it! I wish the car acted like this the whole time

[uberspeed]

Originally Posted by abp689

Reference Mythbusters.

Iirc the general rule of thumb is anything below 40MPH windows down, anything above windows up.

http://www.discovery.com/tv-shows/my...dows-minimyth/

Mythbusters test saw the windows down method clearly win though.

[3.0L]

I could feel a slight load come on the engine of every single AC equipped car I've owned when the AC engaged. This includes Fords, Nissans, Mazda, MB and now my BMW.

The AC load was much more noticeable on the smaller engine cars for sure. I barely notice it on my M235i or GLK350 cars.

My off the cuff guess is that the AC compressors suck several horsepower from the engine. The higher torque your engine, the less likely you'll feel the effects.

[BarryJI]

I'm not complaining about it, just noting some initial effect and wondering how to quantify that. 3.0L, your point about torque is interesting, as it might explain the relatively minimal effect of a/c use on the car's willingness to pull hard.

[Racer20]

The A/C compressor cuts off during WOT. It's a non-issue when accelerating at full throttle.

[CalCarNut]

Barryjj..what Stage1 tune are you going with?

Never noticed any issue with my A/C (yet)........

[Wheelwright]

Originally Posted by jbenington86

Also the amount of power being pulled completely changes how the clutch feels and make it much more difficult to shift. In my wifes 370z no problems at all no matter how low I have the temp.

If it is one thing BMW is not good at.... it is making a poorly designed A/C system

I am a former 128i MT owner and I can confirm that with A/C maxed out throttle response sucked. This was causing revs to drop excessively between gears which forced me to overcompensate. However, this often resulted in jerky gear changes because A/C also made the throttle very sluggish and hard to modulate. I hated driving that car on hot summer day when it was heat-soaked. IMHO massive german engineering fail because a well-designed A/C is crucial to enjoying any car all year.

[BarryJI]

Originally Posted by SoCalDave

Barryjj..what Stage1 tune are you going with?

Never noticed any issue with my A/C (yet)........

SoCalDave, I know you recommend GSR but I am, on first drive, very happy with the Dinan Stage 1. The torque boost is instantly recognizable, as is the increase in HP. The car seems even more willing to rev freely and really takes off under firm throttle input almost anywhere on the RPM range. I have a great relationship with the BMW performance shop near me (Avus, in Glendale) and feel the need to make a distinction between a pretty aggressive tune for street driving on the one hand, and something much more radical that, while exciting, does not carry the same warranty and would, in my case, apply to a car that will never be driven on the track because it is my DD and has all the luxury options.

[CalCarNut]

Congrats on your getting your 228 and enjoy the ride

[CalCarNut]

Will keep Avus in mind for post warranty work on my GC

[jbenington86]

Originally Posted by Wheelwright

I am a former 128i MT owner and I can confirm that with A/C maxed out throttle response sucked. This was causing revs to drop excessively between gears which forced me to overcompensate. However, this often resulted in jerky gear changes because A/C also made the throttle very sluggish and hard to modulate. I hated driving that car on hot summer day when it was heat-soaked. IMHO massive german engineering fail because a well-designed A/C is crucial to enjoying any car all year.

You couldn't of said it any better. I just try and drive with the windows down as much as possible and the A/C off.

[jtzako]

In most modern cars, if you floor it the AC will disengage so it wont be affecting power. However, for normal driving it does have an effect. Smaller engine cars tend to make it more noticeable but in the 228i I havent noticed any drastic change.