BMW 1 Series Coupe Forum / 1 Series Convertible Forum (1M / tii / 135i / 128i / Coupe / Cabrio / Hatchback) (BMW E82 E88 128i 130i 135i)
 





 

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      07-18-2012, 05:59 AM   #45
ShocknAwe
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Quote:
Originally Posted by RPM90 View Post
Normal? NO.
Common? Yes, if your MT skills need work.

You need to practice your MT shifts.
No lazy shifting. Learn to shift quickly all the time.
That way, when the AC brings the engine rpm down quicker, you can shift quickly and smoothly.
Since you know the rpm will drop quicker, then pick a higher rpm to shift.
If you use 2000rpm for a smooth shift, then use 2300 or 2500 when the AC is on, or shift quicker.
No no no, I don't get a jerk at all when going into gear, only when depressing the clutch pedal. I rev match before letting the clutch out.
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      07-18-2012, 06:57 AM   #46
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I still don't understand the comments about smoothness of shifting relative to the AC. Do you have problems going uphill or downhill too? How about while the engine is warming up versus warm? In all these situations the car is behaving a little differently but the difference is small and shouldn't really affect the shifting.

I agree with the "lazy shifting" comments, however. The effort level for my 128i is a little higher than my SUV or other MT cars I have owned. The spring for 5/6 is noticably stronger than I am used to. When I am driving casually, thinking of something else, I sometimes get reminded to push a little harder towards the passengers side if I want 5 or 6. It is not hard to shift my car, it is easier than most MT, but it does require a little more effort than most and I have to not let my mind wander too much.

Pushing the gas pedal a little more compensates for the hp loss for the AC. If I am crusing, that happens naturally without much notice. Accelerating I may notice it's slightly slower. Like it is while warming up. Not a big deal IMHO. When I need the AC it is a good trade.

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      07-18-2012, 07:18 AM   #47
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In every car I've owned.. including this one.. the clutch grab point is different when the AC is on.. I don't know why that happens but, it's annoying as hell.. But power wise, I don't really notice any difference.. it's just annoying to be driving smooth and then not being able to drive smooth with the AC on and have to readjust. Turning DTC on helps though..
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      07-18-2012, 08:13 AM   #48
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I have a 2011 135i with 7DCT and Procede, I can definitely notice a huge difference in performance with the AC on. It is super sluggish and laggy. I swear I lose about 80 hp because it feels worse than running stock maps with AC off. With AC on, even with 75% throttle at 4k rpm at 30 mph (with the boost gauge showing a constant ~10 psi) the acceleration is still so slow. I hear a lot of engine noise, like it is struggling to do what I ask of it. With most of my normal driving with AC off, I rarely use more than 25% throttle, rarely go above 3k rpm (boost gauge rarely shows more than 5 psi briefly), I get a pretty swift kick of that low-end torque and the engine is super smooth and running effortlessly.

Is it possible that Procede is pulling timing or some other safety feature to protect the engine?

I previously had a 2008 335i with 6AT and an earlier version of Procede and did not remember AC having such a huge impact on performance. It was noticeable but not nearly as extreme.
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      07-18-2012, 08:41 AM   #49
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Quote:
Originally Posted by bdoooh View Post
In every car I've owned.. including this one.. the clutch grab point is different when the AC is on.. I don't know why that happens but, it's annoying as hell.. But power wise, I don't really notice any difference.. it's just annoying to be driving smooth and then not being able to drive smooth with the AC on and have to readjust. Turning DTC on helps though..
You "felt" like that but in reality it was really just the rpms dipping down too fast.

The engine adapts to the dipping rpm within the next few shifts.

Also I heard the ECU automatically disconnects the AC on hard accel
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      07-18-2012, 09:09 AM   #50
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2012 135i DCT - can for sure tell the difference in performance with AC on vs off. Sport mode helps to mask the sluggishness.
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      07-18-2012, 09:10 AM   #51
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Having owned many manual transmission cars I can say that they all required a tad more finesse to drive perfectly smooth when the A/C was on. I've also owned a number of turbocharged cars and, in my opinion, running the A/C on those cars was even more noticeable, mainly because the engine was more sluggish than usual off-boost and when boost did hit it was more noticeable than with the A/C off. Plus, turbocharged cars don't like heat and chances are, if you're running the A/C, it's hot out. So, the combined higher ambient temps and the higher engine load caused by the A/C conspire to produce more lag and more noticeable boost onset.

P.S. BMWs have variable displacement A/C compressors. So, unlike many cars that cycle the A/C compressor on and off, the BMW compressors run all the time when the A/C is switched on, varying its displacement to compress lower or higher volumes of refrigerant through the system. This means that the load on the engine won't be consistent; i.e., higher when first turning on the A/C and lower as the cabin temp/selected temp start to equalize. Actually, many European cars operate this way and it's something I've always appreciated about European cars. I hate driving cars where the A/C compressor cycles on and off because you're constantly having to adjust the throttle position because engine power is constantly fluctuating.
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      07-18-2012, 09:29 AM   #52
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Quote:
Originally Posted by Simsims View Post
You "felt" like that but in reality it was really just the rpms dipping down too fast.

The engine adapts to the dipping rpm within the next few shifts.

Also I heard the ECU automatically disconnects the AC on hard accel
Yeah a lot of modern turbo cars do that these days. When you go WOT and activates the WOT table, it'll disable the A/C while you're going WOT.
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      07-18-2012, 01:44 PM   #53
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The engagement point of the clutch has absolutely nothing to do with whether the AC is on. There is a hydraulic cylinder that is directly moved by your foot that pushes fluid through a line to a slave cylinder attached to the clutch. The car's computer is not involved in the activation of the clutch so there is no way for the clutch to change when the AC is on.

I am not trying to say it doesn't feel different but I think the only thing that is changing is the available power from the engine.

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      07-19-2012, 12:58 PM   #54
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Food for thought: When you need/want A/C, it's hot out. Hot air=less dense/less O2=less engine performance.

Sure the A/C clutch contributes a bit, but in these recent 100-110f degree days, the engine computer must be going WTF you feeding me up there!!??
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      07-19-2012, 02:45 PM   #55
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What about on MPG. How much do you guys think the A/C eats up?
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      07-19-2012, 03:14 PM   #56
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Quote:
Originally Posted by JimD View Post
The engagement point of the clutch has absolutely nothing to do with whether the AC is on. There is a hydraulic cylinder that is directly moved by your foot that pushes fluid through a line to a slave cylinder attached to the clutch. The car's computer is not involved in the activation of the clutch so there is no way for the clutch to change when the AC is on.

I am not trying to say it doesn't feel different but I think the only thing that is changing is the available power from the engine.

Jim
Exactly, thing that changes is the reduction in take off torque and it is pretty substantial on the 28 requiring extra throttle and higher shift points and a little more attention to execute smoothly. Despite leaving AC on all the time being "good" (don't think it has to be all the time but I'm sure periodic use is beneficial) generally I don't run it if its not 90+ and humid other than to defrost occasionally. As for MPG I find that if I'm driving locally with AC- pretty big 2-3+ mpg, highway cruise AC on vs. windows open for me equates to little if no change- I can still easily get my coveted 30.1 on the indicator. Why does it go in varying steps of .2 to .6? AC on (hot day) driving back roads spritely is the one instance I have turbo envy in which case I turn it off and sweat it out if I'm by myself.
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Last edited by Monterra; 07-19-2012 at 03:27 PM.
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      07-19-2012, 03:53 PM   #57
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Quote:
Originally Posted by Monterra View Post
... As for MPG I find that if I'm driving locally with AC- pretty big 2-3+ mpg, highway cruise AC on vs. windows open for me equates to little if no change- I can still easily get my coveted 30.1 on the indicator. Why does it go in varying steps of .2 to .6? AC on (hot day) driving back roads spritely is the one instance I have turbo envy in which case I turn it off and sweat it out if I'm by myself.
I read somewhere that under 50 MPH or thereabouts driving with the windows down and A/C off gives the best mileage, but above that reduced aerodynamics takes over and you're better off with windows up and A/C on.
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      07-19-2012, 10:45 PM   #58
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I believe that but for me and my 70-75 range I haven't seen a noticeable difference. Lot of factors at play here- hilly/flat terrain (mine is somewhat hilly), driving style, Cd of the car closed up vs. windows down I'm sure varies pretty wildly per vehicle. One of the things I've come to love about the 1 is how nice and relatively quiet it stays with windows down and roof tilted. I prefer some added aero drag over noticeable driveline drag (maybe in the 35 I wouldn't I drove home the most efficient way today windows up vent on and trip mpg stuck at the proverbial 30.1 same as it was at the start- I reset every tank and turn in a consistent 29.3-30.5 indicated that generally ends up being ~.5mpg optimistic.
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      07-20-2012, 06:51 AM   #59
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Here's an interesting test of a corvette and a VW with no accessories and with AC + headlights + rear defroster on:

http://www.motivemag.com/pub/feature...tic_Loss.shtml

Bottom line is they lost 10hp on the VW and more than 15 on the vette. We haven't talked about electrical loads but they sap power too. I would guess the AC alone is at least half the hp loss. Our ACs seem small to me but it would seem we are losing at least 5hp and possibly 10hp when we run the AC.

The comments about ambient temperature are also correct IMHO. My SUV will ping in hot weather when the plug gap gets a little big on 87 octane. The car computer cannot retard the spark enough to compensate. The AC also makes the car run hotter which compounds the issue. High ambient temperature = less spark advance + AC on both of which reduce power.

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      07-20-2012, 07:59 AM   #60
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my a/c is always on, even when i have the heater on. My car still seems pretty quick. I might get it dynoe'd a/c on v. a/c off.
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      07-20-2012, 10:02 AM   #61
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Instead of cycling the AC compressor on and off BMW apparently changes the volume of what the AC compressor is compressing. That has the same effect of only giving you as much cooling as you need. So if your AC is just switched on but the car doesn't really need to be cooled, you will be losing very little hp. On a really hot day, the compressor will be going flat out and the car may also need to back off on ignition timing to avoid detonation.

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      07-21-2012, 08:49 AM   #62
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I don't seem to notice much difference. Does the fan speed you run the AC at makes a difference?

Reading the thread, it seems to affect N52 more, which makes sense.
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      07-22-2012, 03:32 PM   #63
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Not sure how you could not feel a difference..... A/C takes power to operate. Of course your performance (and fuel mileage) are going to be affected.

I now have a 335i, but YES, there is a noticeable difference when the A/C is on (which is most of the time here in Florida).
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