revs drop faster with AC on?

smeard · 07-02-2018, 02:03 AM

Hey guys, you ever notice when the A/C is on the revs drop so much faster? Kind of makes rev match a PITA. or is it just me??

Been driving stick for years so doubt it is my doing. My old stick shift cars felt different with AC on but not by this much.

Zombie_Head · 07-02-2018, 02:55 AM

My 125i/128i does that, need to shift a bit faster.

Never tried on track with AC on, too damn hot these days, but on the street yes, it is a pain.

Matticus91 · 07-02-2018, 02:08 PM

100% normal. The AC compressor is driven by the motor, so naturally when it's on there's more resistance on the motor (accessory belt) and it will slow faster.

smeard · 07-03-2018, 12:36 AM

Quote:

Originally Posted by Zombie_Head

My 125i/128i does that, need to shift a bit faster.

Never tried on track with AC on, too damn hot these days, but on the street yes, it is a pain.

Indeed jt is, I do find shifting at higher RPMs helps.

smeard · 07-03-2018, 12:38 AM

Quote:

Originally Posted by Matticus91

100% normal. The AC compressor is driven by the motor, so naturally when it's on there's more resistance on the motor (accessory belt) and it will slow faster.

True but never thought it would affect it this much jeez ahahaha. My old manuals felt a bit different with AC on, but with the 1er it's night and day haha

Matticus91 · 07-03-2018, 09:02 AM

Quote:

Originally Posted by smeard

True but never thought it would affect it this much jeez ahahaha. My old manuals felt a bit different with AC on, but with the 1er it's night and day haha

For sure, it's way more noticeable in these cars than other MT cars I've had too. My Mustang GT never even flinched at the AC. Not sure if it has something to do with the load of the AC compressor being higher than other cars or maybe the car's computer intentionally adjusting RPM drop somehow, if that's even possible.

chadillac2000 · 07-03-2018, 10:04 AM

This is definitely a gripe of mine as well. Feels like the pedal engagement point becomes much higher with the AC on, and has gotten even more defined as I've tightened up the drivetrain and transitioned to a SMFW + stiffer clutch.

smeard · 07-03-2018, 09:47 PM

Quote:

Originally Posted by chadillac2000

This is definitely a gripe of mine as well. Feels like the pedal engagement point becomes much higher with the AC on, and has gotten even more defined as I've tightened up the drivetrain and transitioned to a SMFW + stiffer clutch.

How has the SMFW and clutch (Exedy??) been treating you? sometimes I get a little bit of a shudder when I put the clutch in fast, maybe DMFW on its way out.

chadillac2000 · 07-04-2018, 02:41 PM

Quote:

Originally Posted by smeard

How has the SMFW and clutch (Exedy??) been treating you? sometimes I get a little bit of a shudder when I put the clutch in fast, maybe DMFW on its way out.

It's loud with quite a bit of NVH at low RPMs in low gears compared to the DMFW. You get used to it somewhat, but the DMFW shudder is nothing in comparison.

128Styll · 07-08-2018, 03:22 AM

Noticed the same thing this weekend with this heat wave.

Lucky1 · 07-08-2018, 10:18 PM

I guess I must just adapt unconsciously because I've never paid much mind and can rev match just fine with a/c on. More annoyed about the overall drop in power when the a/c is on which sometimes ranges from subtle to fairly noticeable. I find the gearbox and clutch smooth as silk though following my diff and gearbox fluid changes to Redline and in that regard a the smoothness of shifting is a very good match to the smoothness of the N52.

asiflicious · 07-09-2018, 03:22 AM

Speaking of, is it just me or do the brakes feel far weaker with the AC on? I've noticed it in both my 128i and 135i

smeard · 07-10-2018, 05:49 PM

Quote:

Originally Posted by 128Styll

Noticed the same thing this weekend with this heat wave.

Yes it is very noticeable where I’m at (110+ Fahrenheit)

smeard · 07-10-2018, 05:51 PM

Quote:

Originally Posted by Lucky1

I guess I must just adapt unconsciously because I've never paid much mind and can rev match just fine with a/c on. More annoyed about the overall drop in power when the a/c is on which sometimes ranges from subtle to fairly noticeable. I find the gearbox and clutch smooth as silk though following my diff and gearbox fluid changes to Redline and in that regard a the smoothness of shifting is a very good match to the smoothness of the N52.

got my 1er with ~53k on the clock, now has about 56k. Could probably use a diff/trans fluid flush next oil change

07-02-2018, 02:03 AM	#1
smeard First Lieutenant 136 Rep 316 Posts Drives: BMW Join Date: Jan 2018 Location: CA iTrader: (0) Garage List 2010 BMW 128i [0.00]	revs drop faster with AC on? Hey guys, you ever notice when the A/C is on the revs drop so much faster? Kind of makes rev match a PITA. or is it just me?? Been driving stick for years so doubt it is my doing. My old stick shift cars felt different with AC on but not by this much. __________________ Commuter- F10 528i N20 8AT Jatoba Black Show- F10 550i M sport 8AT Alpine White: Airrex Bags, 20" Forgestar F14s, Meisterschaft Catback Around town- E60 528i N52, 6AT, Monaco Blue Weekend - 1997 BMW Z3 M52, 5spd, Dunkelgrun: 230k mi, Intrax Springs on Bilsteins, Style 68s staggered AutoX/track - 2012 F30 N20, 6MT BSM
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07-02-2018, 02:55 AM	#2
Zombie_Head Captain 594 Rep 704 Posts Drives: E30 325i 4-Door Join Date: Dec 2017 Location: Bavaria iTrader: (0)	My 125i/128i does that, need to shift a bit faster. Never tried on track with AC on, too damn hot these days, but on the street yes, it is a pain.
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07-02-2018, 02:08 PM	#3
Matticus91 Brigadier General 3475 Rep 3,722 Posts Drives: 2013 135i Join Date: Aug 2015 Location: Washington DC iTrader: (6)	100% normal. The AC compressor is driven by the motor, so naturally when it's on there's more resistance on the motor (accessory belt) and it will slow faster. __________________ "Tobias" 2013 135i ///M-Sport 6MT • Pure Stage 1 • XDI 35 HPFP • 404whp/440wtq IG: msteelio91
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07-03-2018, 10:04 AM	#7
chadillac2000 Major 1220 Rep 1,372 Posts Drives: 2015 BMW M3 Join Date: Nov 2008 Location: Asheville, North Carolina iTrader: (7)	This is definitely a gripe of mine as well. Feels like the pedal engagement point becomes much higher with the AC on, and has gotten even more defined as I've tightened up the drivetrain and transitioned to a SMFW + stiffer clutch. __________________ 2008 BMW 135i Single Turbo Build Thread HERE 2016 BMW M5 Competition Build Thread HERE 2015 BMW M3 Build Thread HERE
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07-08-2018, 03:22 AM	#10
128Styll Colosseum Chariot Driving Instructor 4 Rep 21 Posts Drives: Slow '12 128i Join Date: Jul 2018 Location: SoCal iTrader: (0)	Noticed the same thing this weekend with this heat wave.
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07-08-2018, 10:18 PM	#11
Lucky1 Colonel 647 Rep 2,051 Posts Drives: '08 128i Coupe SGM 6MT Join Date: Nov 2008 Location: Toronto iTrader: (0) Garage List 2015 Porsche 911 Ca ... [0.00] 2008 128i Coupe [0.00] 2006 Z4 M Roadster [0.00]	I guess I must just adapt unconsciously because I've never paid much mind and can rev match just fine with a/c on. More annoyed about the overall drop in power when the a/c is on which sometimes ranges from subtle to fairly noticeable. I find the gearbox and clutch smooth as silk though following my diff and gearbox fluid changes to Redline and in that regard a the smoothness of shifting is a very good match to the smoothness of the N52.
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07-09-2018, 03:22 AM	#12
asiflicious Captain 690 Rep 968 Posts Drives: 2018 M2 Join Date: Aug 2017 Location: Winchester, CA iTrader: (0) Garage List 2018 BMW M2 [10.00]	Speaking of, is it just me or do the brakes feel far weaker with the AC on? I've noticed it in both my 128i and 135i
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