How does running A/C effect performance???
Thread Starter
Safety Car
Joined: Sep 2000
Posts: 3,524
Likes: 4
From: Hinckley Ohio
How does running A/C effect performance???
I think that the A/C disengages when you go WOT, but I can't find anything that describes how this works.
Do you have to go 100% WOT before it disengages, is there a time delay, when does it re-engage??
If you were to run at the dragstrip with the A/C on vs A/C off would you see any difference?? Has anyone done it, that is, compare strip results with A/C on vs A/C off??
Do you have to go 100% WOT before it disengages, is there a time delay, when does it re-engage??
If you were to run at the dragstrip with the A/C on vs A/C off would you see any difference?? Has anyone done it, that is, compare strip results with A/C on vs A/C off??
Melting Slicks
Joined: Jan 2000
Posts: 3,418
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From: NW Chicago Suburbs
Re: How does running A/C effect performance??? (LT4BUD)
Most strips want the AC off so water isn't dripped on the track. If the car loses traction on one side due to AC water...it can get ugly real fast.
Eric
Eric
Thread Starter
Safety Car
Joined: Sep 2000
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From: Hinckley Ohio
Re: How does running A/C effect performance??? (silver & red CE)
That is interesting, I haven't been to the strip in many years but I would quess most racers would turn their A/C off. Anyhow I quess this means no one is going to have any actual timeslips to compare.
So lets say theoretically I am on the street at a red light with the A/C on and suddenly I have the need for maximum acceleration and I forget to turn off the A/C. How much performance have I lost by not turning off the A/C????
So lets say theoretically I am on the street at a red light with the A/C on and suddenly I have the need for maximum acceleration and I forget to turn off the A/C. How much performance have I lost by not turning off the A/C????
Thread Starter
Safety Car
Joined: Sep 2000
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From: Hinckley Ohio
Re: How does running A/C effect performance??? (scorp508)
Am I correct when I state that at least on a 96 LT4 the A/C turns off at WOT?? If early C4's don't, when did they make the change, if ever???
Maybe the A/C doesn't turn off & that is why I couldn't find it in the shop manual??
Do you guys turn off your A/C before a maximum performance run on the street???
Maybe the A/C doesn't turn off & that is why I couldn't find it in the shop manual??
Do you guys turn off your A/C before a maximum performance run on the street???
Drifting
Joined: Nov 2002
Posts: 1,365
Likes: 3
From: Huntsville AL
Re: How does running A/C effect performance??? (LT4BUD)
I leave the A/C on right up until I stage. It turns both fans on and keeps my engine from hitting 227 degrees.
I've got a '94 and I'm pretty sure the clutch disengages at WOT. Incidentally, when a friend and I were at the strip last Friday night, one of the workers asked him if he had his A/C off before he rolled up to the lights. I didn't know at the time why he asked that, but now I do :thumbs:
I've got a '94 and I'm pretty sure the clutch disengages at WOT. Incidentally, when a friend and I were at the strip last Friday night, one of the workers asked him if he had his A/C off before he rolled up to the lights. I didn't know at the time why he asked that, but now I do :thumbs:
Drifting
Joined: Jun 2002
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From: Iowa
Cruise-In IV Veteran
Cruise-In V Veteran
Re: How does running A/C effect performance??? (LT4BUD)
I have heard that running the a/c will cost you 10 hp. No one in their right mind would run their a/c at the drag strip, unless they relish the thought of losing.
Your cars a/c does not shut off at any WOT speed. However, I believe, if my memory serves me right, it you rev it too high, the compressor goes into "float" mode where a bypass valve opens internally to prevent overpressurizing the system.
If you happen to want to accelerate off the line quickly and leave the a/c unit on, you will go accelerate slower.....not much but you'll notice it. And yes, if I think I am going to want to take off fast, (to keep up with the surrounding traffic, of course), I flip the a/c off.
Your cars a/c does not shut off at any WOT speed. However, I believe, if my memory serves me right, it you rev it too high, the compressor goes into "float" mode where a bypass valve opens internally to prevent overpressurizing the system.
If you happen to want to accelerate off the line quickly and leave the a/c unit on, you will go accelerate slower.....not much but you'll notice it. And yes, if I think I am going to want to take off fast, (to keep up with the surrounding traffic, of course), I flip the a/c off.
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Le Mans Master
Joined: Dec 2000
Posts: 7,839
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From: San Diego, Ca
Re: How does running A/C effect performance??? (LT4BUD)
Depending on year and make, GM A/C is either totally controlled by the ECM or has a circuit to the ECM which must be completed for the clutch to engage. The ECM opens the clutch circuit with a full throttle signal from the TPS or a high load signal from the MAP (if so equipped). My seat of the pants experience tells me there's a brief time delay but a scan capture where you monitor TPS voltage with A/C request would be one possible way to verify it.
Le Mans Master
Joined: Dec 2000
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From: San Diego, Ca
Re: How does running A/C effect performance??? (SunCr)
I should add there isn't any "float" mode for the compressor. If pressure gets too high, a switch cuts it off. Also if the ECM isn't responding to the a/c request circuit, you're idle quality will usually be poor, most not even driveable. Up until at least the '90, the ECM A/C circuit was at PIN B8. For manual air, there should be 12 volts on this circuit with a/c requested. For electronic, 5 to 7. If you have the voltage and the ECM isn't adjusting idle or if the compressor isn't kicking out at full throttle, the ECM is probably bad. Easiest to verify with a scan.
Team Owner
Joined: Mar 2000
Posts: 83,383
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From: Boston, MA
Re: How does running A/C effect performance??? (Aaron's 87)
There's a spot in 6E code (89) for TPS% to disengage A/C clutch. The factory set it at 100%, I set it lower.
Le Mans Master
Joined: Dec 2000
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From: San Diego, Ca
Re: How does running A/C effect performance??? (scorp508)
Sorry, I don't speak the language, so what is 6E code? Section 6E of the Shop Manual is the ECM section, but I'm sure you're referring to something else. Also, is the load variable a parameter for an '89?
Team Owner
Joined: Mar 2000
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From: Boston, MA
Re: How does running A/C effect performance??? (SunCr)
Also, doesn't the ECM consider anything over 4 volts 100%?
Le Mans Master
Joined: Dec 2000
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From: San Diego, Ca
Re: How does running A/C effect performance??? (scorp508)
So if the ECM sees 69% is that 100% as far as the a/c is concerned or is looking for the full 5 volts, which as you pointed out, is pretty much impossible? Can't believe it was designed that way since my seat of the pants test feels otherwise - and that's in all of my GM vehicles (94 Sonoma, 97 S10 & a '95 Gran Prix along with the Vette). Anyway, it's a little confusing to me. Thanks.
Team Owner
Joined: Mar 2000
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From: Boston, MA
Re: How does running A/C effect performance??? (SunCr)
So if the ECM sees 69% is that 100% as far as the a/c is concerned or is looking for the full 5 volts, which as you pointed out, is pretty much impossible?
Le Mans Master
Joined: Dec 2000
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From: San Diego, Ca
Re: How does running A/C effect performance??? (scorp508)
I still don't know what 6E code is, but I'd like a shot at the engineer or programmer who decided - say on your Vette, that 3.69 volts was the parameter to dump max fuel, optimize timing, but leave the a/c clutch engaged until it got a full 5 volts from the TPS.
Team Owner
Joined: Mar 2000
Posts: 83,383
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From: Boston, MA
Re: How does running A/C effect performance??? (SunCr)
I still don't know what 6E code is
ECM: 1227165
Cars: 89 Y & F CAR 5.0L & 5.7L
http://www.tunercat.com/pdfs/ecm_$6e.pdf
Race Director
Joined: Feb 2003
Posts: 18,484
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From: Everyday you must choose between the pain of discipline and the pain of regret. Fredericktown, OH
Re: How does running A/C effect performance??? (LT4BUD)
Wow, this conversation went over my head in a hurry.
But, the AC is driven by the belt which is in turn driven by the crank. Running the AC creates extra drag on the motor, robbing it of a bit of HP. This concept is why nearly all regular drag racers run electric water pumps and fans - to not rely on the motor to turn the pump and using the HP (and to be able to cool the car between runs). When I had the race car, I knew several people who actually disengaged the alternator for a run under the same premise. It was a PITA always having to charge between runs, but some people will go to extreems to get the HP the have to the track.
But, the AC is driven by the belt which is in turn driven by the crank. Running the AC creates extra drag on the motor, robbing it of a bit of HP. This concept is why nearly all regular drag racers run electric water pumps and fans - to not rely on the motor to turn the pump and using the HP (and to be able to cool the car between runs). When I had the race car, I knew several people who actually disengaged the alternator for a run under the same premise. It was a PITA always having to charge between runs, but some people will go to extreems to get the HP the have to the track.