how much HP do you loose if you race with the A/C on?
Registered User
Joined: Jan 2003
Posts: 256
From: Fayetteville NC
Originally posted by sc1twntrbo
now that i read all this i realize that droping the ac would give me 100 hp at the rear wheels. now i get most of that hp from the stickers i bought to tell everyone about my mod.
now that i read all this i realize that droping the ac would give me 100 hp at the rear wheels. now i get most of that hp from the stickers i bought to tell everyone about my mod.
Registered User
Joined: Oct 2002
Posts: 2,931
From: Upstate NY
Originally posted by treyZ28
what I dont understand is how a mere 10hp loss in the pullies can cause this massive gas milage drop everyone rants about.
I drive with AC on constantly and just got 17mpg in my truck- 30% city.
Thats like saying an aluminum driveshaft or electric water pump will significanly increase my gas milage
I mean i can see .25 mpg but 5mpg that everyone claims? I dont think its a big enough resistance to cause that much trouble
what I dont understand is how a mere 10hp loss in the pullies can cause this massive gas milage drop everyone rants about.
I drive with AC on constantly and just got 17mpg in my truck- 30% city.
Thats like saying an aluminum driveshaft or electric water pump will significanly increase my gas milage
I mean i can see .25 mpg but 5mpg that everyone claims? I dont think its a big enough resistance to cause that much trouble
Now consider a small 1.6L engine dragging an econobox around. Sure it takes a few hp less to cruise, but the little engine might only have the potential for 40 hp at cruise rpm. The compressor is about the same so it still absorbs 5 hp, a much larger % of the available power. So, the little engine has to produce more of it's maximum, it uses significantly more fuel, and mileage suffers more.
Where you really notice it is in acceleration before the compressor cuts out at WOT. I've driven underpowered s-boxes in the mountains where you had to turn off the A/C to barely keep up with traffic.
It might be interesting if the EPA rated mileage with both a/c on and off.
Registered User
Joined: Apr 2003
Posts: 1,591
From: PA
I can't find any references to back this up but,
Doesn't rolling the windows up and turning on the AC improve gas milage because the slightly better aerodynamics, assuming highway speeds. The loss the the compressor is negated by the improved aerodynamics. Now if you had the windows up and the AC off that would obviously be better, but usually if you are considering putting the AC on you would be dropping the windows to keep cool instead.
OldSS, you mentioned that some cars shut off above a certain RPM to protect the compressors, but not on fbodys. The more i think about it that 3k rpm cutoff i mentioned might not have been for our cars, but rather York compressors. In jeeps (amc's) they used york compressors with an oil type lubrication instead of releying on the freon for lubrication. Thus you can use it as an onboard air system compressor for filling tires and running air tools. With a 10.3 ci york compressor there is severly diminishing returns from spinning it faster than 2500 rpm, you don't get anymore flow out of them. That is probably where I got that 3K number from. I'm not sure though, bottom line is that some cars do cut out based on RPM and all/most do under full throttle.
Doesn't rolling the windows up and turning on the AC improve gas milage because the slightly better aerodynamics, assuming highway speeds. The loss the the compressor is negated by the improved aerodynamics. Now if you had the windows up and the AC off that would obviously be better, but usually if you are considering putting the AC on you would be dropping the windows to keep cool instead.
OldSS, you mentioned that some cars shut off above a certain RPM to protect the compressors, but not on fbodys. The more i think about it that 3k rpm cutoff i mentioned might not have been for our cars, but rather York compressors. In jeeps (amc's) they used york compressors with an oil type lubrication instead of releying on the freon for lubrication. Thus you can use it as an onboard air system compressor for filling tires and running air tools. With a 10.3 ci york compressor there is severly diminishing returns from spinning it faster than 2500 rpm, you don't get anymore flow out of them. That is probably where I got that 3K number from. I'm not sure though, bottom line is that some cars do cut out based on RPM and all/most do under full throttle.
Registered User
Joined: Nov 1998
Posts: 538
From: valencia,california,u.s.a.
Well I did blow my compresor while blasting the car getting on the freeway,but I had extended warranty,and it picked up all but $50.00 of the tab.If the car does have cut off switch,I don't believe it reacted fast enough to disengage the compressor.I don't run the air if I know I'm gona blast it anymore.Cost to the insurance company was about $1,500.That you can take to the bank.Or take it out of the bank for when it does happen.M02
Registered User
Joined: Oct 2002
Posts: 2,931
From: Upstate NY
Originally posted by 94formulabz
I can't find any references to back this up but,
Doesn't rolling the windows up and turning on the AC improve gas milage because the slightly better aerodynamics, assuming highway speeds. The loss the the compressor is negated by the improved aerodynamics. Now if you had the windows up and the AC off that would obviously be better, but usually if you are considering putting the AC on you would be dropping the windows to keep cool instead.
You hit it. Especially at higher freeway speeds, closed windows are the way to go.
My pet peeve is the person who is running the automatic A/C with a window partially down on a hot day. It's often a smoker.
The A/C sensors around the instrument panel detect the warm air and keep delivering cold air. It can't catch up, so compressor runs all the time. Besides, A/C also dehumidifies, and if it's humid outside, the open window spoils that.
Same scenerio in the winter: open window = cold air to sensors and more heat from the floor outlets. It's hard to get comfortable, and rear seat passengers freeze. Been there, experienced that. The person had a blanket for rear seat pasengers and blamed the poor heat/vent system of the car!
My Vette has an instantaneous mileage computer mode. I've tried many different combinations of a/c on/off, windows up/down, top on/off with interesting results.
OldSS, you mentioned that some cars shut off above a certain RPM to protect the compressors, but not on fbodys. The more i think about it that 3k rpm cutoff i mentioned might not have been for our cars, but rather York compressors. In jeeps (amc's) they used york compressors with an oil type lubrication instead of releying on the freon for lubrication. Thus you can use it as an onboard air system compressor for filling tires and running air tools. With a 10.3 ci york compressor there is severly diminishing returns from spinning it faster than 2500 rpm, you don't get anymore flow out of them. That is probably where I got that 3K number from. I'm not sure though, bottom line is that some cars do cut out based on RPM and all/most do under full throttle.
I can't find any references to back this up but,
Doesn't rolling the windows up and turning on the AC improve gas milage because the slightly better aerodynamics, assuming highway speeds. The loss the the compressor is negated by the improved aerodynamics. Now if you had the windows up and the AC off that would obviously be better, but usually if you are considering putting the AC on you would be dropping the windows to keep cool instead.
You hit it. Especially at higher freeway speeds, closed windows are the way to go.
My pet peeve is the person who is running the automatic A/C with a window partially down on a hot day. It's often a smoker.
The A/C sensors around the instrument panel detect the warm air and keep delivering cold air. It can't catch up, so compressor runs all the time. Besides, A/C also dehumidifies, and if it's humid outside, the open window spoils that.
Same scenerio in the winter: open window = cold air to sensors and more heat from the floor outlets. It's hard to get comfortable, and rear seat passengers freeze. Been there, experienced that. The person had a blanket for rear seat pasengers and blamed the poor heat/vent system of the car!
My Vette has an instantaneous mileage computer mode. I've tried many different combinations of a/c on/off, windows up/down, top on/off with interesting results.
OldSS, you mentioned that some cars shut off above a certain RPM to protect the compressors, but not on fbodys. The more i think about it that 3k rpm cutoff i mentioned might not have been for our cars, but rather York compressors. In jeeps (amc's) they used york compressors with an oil type lubrication instead of releying on the freon for lubrication. Thus you can use it as an onboard air system compressor for filling tires and running air tools. With a 10.3 ci york compressor there is severly diminishing returns from spinning it faster than 2500 rpm, you don't get anymore flow out of them. That is probably where I got that 3K number from. I'm not sure though, bottom line is that some cars do cut out based on RPM and all/most do under full throttle.
Registered User
Joined: Nov 2001
Posts: 43
From: CORAL SPRINGS, FL, USA
If your A/C doesn't affect your H/P then why did i run a 14.0 @ 99 mph with the a/c blasting (accedint) with the SAME 60 ft time as the 13.7. i have an automatic by the way (shifting wasnt the problem).
Registered User
Joined: Oct 2002
Posts: 2,931
From: Upstate NY
Originally posted by 97ZBOY
If your A/C doesn't affect your H/P then why did i run a 14.0 @ 99 mph with the a/c blasting (accedint) with the SAME 60 ft time as the 13.7. i have an automatic by the way (shifting wasnt the problem).
If your A/C doesn't affect your H/P then why did i run a 14.0 @ 99 mph with the a/c blasting (accedint) with the SAME 60 ft time as the 13.7. i have an automatic by the way (shifting wasnt the problem).
Registered User
Joined: Jun 2003
Posts: 3,620
From: Saginaw, Michigan
Unless one of you guys can measure the hp loss, I refuse to believe that it's only 5 hp or so. Any of you with a M6 will know what I'm talking about. There is a huge difference on my engine with the compresser on. The engine RPM goes down MUCH faster between shifts, and I can feel a lot less throttle response and power with the A/C on. Maybe my car is a freak, but I can tell a HUGE difference with the A/C on. You probably wouldn't notice it nearly as much in an A4, but I sure can.
I would never race with it on.
Dan
I would never race with it on.
Dan
