# LOsing HP with AC



## kaintkwit (May 28, 2005)

*I constantly avoid using my AC for fear of sitting sluggishly at lights. Everytime I turn it on my car starts acting like a tortoise. I recently added a short ram intake but I was wondering other than the echaust I am getting ready have made, what else could I do to avoid this loss in power?* :waving:


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## psuLemon (Apr 23, 2003)

UR underdrive pulley is really the only thing that will help.


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## dmp316 (Aug 5, 2004)

kaintkwit said:


> *I constantly avoid using my AC for fear of sitting sluggishly at lights. Everytime I turn it on my car starts acting like a tortoise. I recently added a short ram intake but I was wondering other than the echaust I am getting ready have made, what else could I do to avoid this loss in power?* :waving:


I have the same problem, pullies will help this i think. :cheers:


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## thestunts200sx (Jul 11, 2005)

just the UR pulley....or dont turn it on.....


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## Ninety-Nine SE-L (May 5, 2002)

IT REALLY GIVES ME A HEADAKE WHN PEOPLE TYPE WITH RAELLY BIG LETTERS AND DONT READ WAHT THEYRE TYPIG. YOU WOULD ALMOST THIKN THE WORLS WAS GONNA END BEKAUSE YOUR AC IS ROBING YOU OF HORSEPOWA. i THINK IT MAY BE BECAUZ YOUR CAR IS TOO SLOW OR MAYBE IR'S DUE TO THE FAKT THAT ACCESSORIEZ ARE PRONE TO ROBBING *ALL* ENGINNS OF POWER.

Sorry, but that's the fact, if you can live without A/C, go for it, I almost never use my AC and I'm in FL. I hate AC, I have a 200-crank hp SR20 and it robs me of power as well, not to mention, it makes my idle so bad I stall all the time (due to my cams). I have UR pulleys, it helps a tiny bit, but I can still see a DRAMATIC difference when my AC is on or off.

If you want the power, turn off the AC, if you want the comfort, turn it back on. If you live in Canada, rip that fuggin thing out of your car. Unless you're having trouble reaching "Merging" velocity, or you're showing the red 1.5L civic on your left 'who's got the cajones,' Just live with the 2-3horses your AC is robing you of, you have a good 86 of them left.

And please don't act like it's the end of the world, I think that font just raised homeland security up to level orange.


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## Nismo GA16 (Mar 22, 2005)

Ninety-Nine SE-L said:


> IT REALLY GIVES ME A HEADAKE WHN PEOPLE TYPE WITH RAELLY BIG LETTERS AND DONT READ WAHT THEYRE TYPIG. YOU WOULD ALMOST THIKN THE WORLS WAS GONNA END BEKAUSE YOUR AC IS ROBING YOU OF HORSEPOWA. i THINK IT MAY BE BECAUZ YOUR CAR IS TOO SLOW OR MAYBE IR'S DUE TO THE FAKT THAT ACCESSORIEZ ARE PRONE TO ROBBING *ALL* ENGINNS OF POWER.
> 
> Sorry, but that's the fact, if you can live without A/C, go for it, I almost never use my AC and I'm in FL. I hate AC, I have a 200-crank hp SR20 and it robs me of power as well, not to mention, it makes my idle so bad I stall all the time (due to my cams). I have UR pulleys, it helps a tiny bit, but I can still see a DRAMATIC difference when my AC is on or off.
> 
> ...


^ lmao! yeah i live in SOUTH! Florida and i never use it... Only when giving the Presidental Treatment to the Little Lady or my Mom lmao!... if i can make it down here that i think any 1 can make it with out a little A/C


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## WiZzO (Jun 15, 2005)

i agree i also live in south florida and my passenger window doesnt go down but my window and that sun roof work fine so ummm...whats ac? but i think i know what he is talking about, i know for me its a lot more than 2 or 3 horses cause when it is on i can be WOT from a light and people driving normal are passing me and people are honking and crap like that lol its pretty funny


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## IanH (Feb 11, 2003)

WiZzO said:


> i agree i also live in south florida and my passenger window doesnt go down but my window and that sun roof work fine so ummm...whats ac? but i think i know what he is talking about, i know for me its a lot more than 2 or 3 horses cause when it is on i can be WOT from a light and people driving normal are passing me and people are honking and crap like that lol its pretty funny


My A/C is over charged and hits the high side switch, and really drags the car down. However it works great on the highway. 
If the normal A/c is 200 lbs pressure and the high side pressure is 500 lbs then 3 hp becomes 7.5 Hp........


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## Ninety-Nine SE-L (May 5, 2002)

BTW, did I mention it sucks up gas too? When I'm on the highway, I leave the sunroof tilted and the fan blowing, that way I have air flowing through the car with no drag.


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## thestunts200sx (Jul 11, 2005)

Running your AC has no adverse affect on your cars gas mileage ....

Read it in a Car & Driver .... and just to see, I ran my car with a full tank of gas normal driving, not gasing it after corners or anything, and got about 380 mpg, then filled it up, and drove with the ac on no matter where i went and time of day...was always on full max....and got 370mpg ....

But I could be wrong....only drawback is the hp loss, so most people end up pushing hard to get the car to go normal, which will yes eat more gas.....


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## Ninety-Nine SE-L (May 5, 2002)

thestunts200sx said:


> Running your AC has no adverse affect on your cars gas mileage ....
> 
> Read it in a Car & Driver .... and just to see, I ran my car with a full tank of gas normal driving, not gasing it after corners or anything, and got about 380 mpg, then filled it up, and drove with the ac on no matter where i went and time of day...was always on full max....and got 370mpg ....
> 
> But I could be wrong....only drawback is the hp loss, so most people end up pushing hard to get the car to go normal, which will yes eat more gas.....


I have an ECU reader that I got on SR20forum (very nice device BTW, made by a member). I am able to moniter my fuel injector pulse width and duty cycle. If I put the cruise control on at 70 and moniter the injectors, they will remain at a constant 14-15% duty on level ground, going uphill the number can get up to 25%, going downhill the number can go down to 8%, all traveling at a constant speed and RPM.

If I'm on level ground and I put the AC on full blast, the number wll go from 14-15% to about 19-21%. Keeping in mind I have 259cc injectors, the injectors are pushing ~51cc/min vs ~38cc/min, just by turning on the AC.


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## RBI*04 (Sep 10, 2004)

good god!!! my B13 is horrible w/o AC. and i live in NEW YORK!!! anything under 10mph and ill breake a sweat. idk how you guys do it in FLA


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## Token Moron (Mar 28, 2003)

you will feel that drag in no matter what car youre in..the only real thing that will solve this issue are underdrive pulleys.


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## IanH (Feb 11, 2003)

Ninety-Nine SE-L said:


> I have an ECU reader that I got on SR20forum (very nice device BTW, made by a member). I am able to moniter my fuel injector pulse width and duty cycle. If I put the cruise control on at 70 and moniter the injectors, they will remain at a constant 14-15% duty on level ground, going uphill the number can get up to 25%, going downhill the number can go down to 8%, all traveling at a constant speed and RPM.
> 
> If I'm on level ground and I put the AC on full blast, the number wll go from 14-15% to about 19-21%. Keeping in mind I have 259cc injectors, the injectors are pushing ~51cc/min vs ~38cc/min, just by turning on the AC.


Thanks for real data. 
Using this I calculate 29 mpg with A/C off vs 21.6 with A/C on
Does this seem correct to you ?


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## Ninety-Nine SE-L (May 5, 2002)

IanH said:


> Thanks for real data.
> Using this I calculate 29 mpg with A/C off vs 21.6 with A/C on
> Does this seem correct to you ?


2 things you're wrong about, you apparently did some really shitty math, and oh wait, I'm a M.E. with a math minor.

first off, duty cycle only one of the MANY variables that lead to the equation of fuel consumption. 51cc/min is nothing when the injector has a pulse width of 5ms. Here's the simplified equation:
[injector cc * (duty cycle%) / 60sec / 1000milisec] * pw * RPM/2 * #ofCyl's
this will eventually give you ACTUAL CC/Min. Take the actual speed in MPH and you'll see how many CC per mile and how many miles per gallon.

second, here's my overly simple equation to your problem. It's not accurate, but it's a good estimate. I'm getting about 15% w/o AC and 20% w/ AC.
100-15=85
100-20=80

if you're making 29MPG w/o AC, then:

(29/85) = (X/80), X = 27.29MPG w/ AC


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## SUPERSTEVE'S200SX (Feb 24, 2004)

Ninety-Nine SE-L said:


> 2 things you're wrong about, you apparently did some really shitty math, and oh wait, I'm a M.E. with a math minor.
> 
> first off, duty cycle only one of the MANY variables that lead to the equation of fuel consumption. 51cc/min is nothing when the injector has a pulse width of 5ms. Here's the simplified equation:
> [injector cc * (duty cycle%) / 60sec / 1000milisec] * pw * RPM/2 * #ofCyl's
> ...





Yeah thats pretty much right on becuz if you think about it windows down and sunroof open you have a lot of drag which will in the same effect take more gas versus running the a/c being nice and cool and still getting decent gas milage, I would agree dont worry about the hp just stay cool and use that car to get from location a to location b


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## IanH (Feb 11, 2003)

Ninety-Nine SE-L said:


> 2 things you're wrong about, you apparently did some really shitty math, and oh wait, I'm a M.E. with a math minor.
> 
> first off, duty cycle only one of the MANY variables that lead to the equation of fuel consumption. 51cc/min is nothing when the injector has a pulse width of 5ms. Here's the simplified equation:
> [injector cc * (duty cycle%) / 60sec / 1000milisec] * pw * RPM/2 * #ofCyl's
> ...


Ok I don’t pretend to understand the intricacies of Fuel injection algorithms if that’s what you are trying to show. Yes your explanation of "flow rate" vs. "flow actual" does help. 

As for my shitty math I took your quoted fuel usage rate at 70 mph and calculated the mpg using excel. I.e. from 
"The injectors are pushing ~51cc/min vs ~38cc/min, just by turning on the AC." 
Unfortunately you did not give what you later called "actual cc/min" above . 

So you are saying these numbers are not right then say my math is wrong?? 

You clearly show the duty cycle going up with load, then use (100 - duty cycle) to work out the ratio? That’s not right. 


From your formula 

MPG = 70mph/ fuel usage rate in gallons = 70*3789*60/fuel usage in cc/min 
so its proportional to 1/ fuel usage cc/min 

SO MPG1 proportional to 1/ *[injector cc * (duty cycle%1) / 60sec / 1000milisec] * pw * RPM/2 * #ofCyl's 

MPG2/ MPG1 = [injector cc * (duty cycle%1) / 60sec / 1000milisec] * pw * RPM/2 * #ofCyl's/ 
[injector cc * (duty cycle%2) / 60sec / 1000milisec] * pw * RPM/2 * #ofCyl's 

If you don’t give the pw as a variable I will call it fixed. 

MPG2 = MPG1 *(duty cycle%1)/ duty cycle%2) 

So if usage is 51cc to 38 cc you should ratio these numbers. 

I.e. 30 mpg without A/C * 38/51 = 22.4 mpg.


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## Ninety-Nine SE-L (May 5, 2002)

Many times, I hear the term the simplest answer is the best answer. I'm not sure which is the case in this situation, but which # do you think is closer to the correct number?

starting with 29MPG base, would the AC drop it to ROUGHLY:
a. 21MPG?
b. 27MPG?
c. 22MPG?

I know AC will decrease your fuel economy, I REALLY, REALLY doubt it's as high as 7-8MPG, but that's your call. All I'm saying is when I turn on the AC, the little thinga-ma-jigger, goes from "15%" to "20%" end of story.

Some people in here are saying that AC doesn't affect fuel economy due to the fact that the speed remains constant. Well then, I guess we can call this 'free energy.' The fact is, the more load you put on an engine, the more air/fuel it takes to maintain a constant RPM. Here's a little homework assignment, get on the highway, bring the car to a constant speed and turn on the cruise control. Now, drive the car up a steep hill and see what happens to the accelerator petal. *gasp* more load has been put on the engine, therefore it requires more fuel and throttle to maintain a constant speed.


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## CHRIS/SR/SE (Dec 15, 2003)

apples to oranges, my Nissan looses around 3-4 mpg with the ac on, oddly enough my girl's car looses so little it's not measurable (she has the SOHC 2.0L)


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## Chuck (Nov 19, 2003)

Hey man, this could definatly help you out..

http://cgi.ebay.com/ebaymotors/TORQ...ryZ33597QQrdZ1QQcmdZViewItem#ebayphotohosting

it says in the description 

"REDUCES FEELING OF HELPLESSNESS YOU MAY GET WHEN TURNING AIR CONDITIONER"


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## Ninety-Nine SE-L (May 5, 2002)

damn, they're really getting serious with those things. They went from a resitor wrapped in duct tape to a complete "SUSTEM" with wiring harness and even its own box, lol. It fits my mom's camry and my skyline, I guess I'll have to get 2.


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## psuLemon (Apr 23, 2003)

its EBAY made, it can't be good


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## stone (Jul 7, 2005)

Chuck said:


> Hey man, this could definatly help you out..
> 
> http://cgi.ebay.com/ebaymotors/TORQ...ryZ33597QQrdZ1QQcmdZViewItem#ebayphotohosting
> 
> ...


How does this thing work??


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## Ninety-Nine SE-L (May 5, 2002)

stone said:


> How does this thing work??


haha, it's the latest in automotive engineering. This revolutionary unit works by fooling the driver into thinking his car is faster. :thumbdwn:


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## timothyc1234 (Oct 14, 2003)

Chuck said:


> Hey man, this could definatly help you out..
> 
> http://cgi.ebay.com/ebaymotors/TORQ...ryZ33597QQrdZ1QQcmdZViewItem#ebayphotohosting
> 
> ...


holy sheet that's funny dude. while you're at it i'll sell you some muffler bearings and a framel valve.


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## HATEnFATE (Dec 24, 2002)

You'll get better gas mileage on the freeway with the A/C on and windows up then you will with the A/C off and windows down due to drag.

Whats funny is everyone is trying to draw out equations to prove how bad the fuel economy really is. Who cares..............

If your gonna complain about A/C then buy a damned V8 engine in which you wont feel any parasitic drag from any accessory. When you bought your 4 cyl. car you KNEW what accessories did. Deal with it.


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## black97ser (May 5, 2005)

timothyc1234 said:


> holy sheet that's funny dude. while you're at it i'll sell you some muffler bearings and a framel valve.


hey timothyc1234 my muffler bearings are fine, but would you happen to have any greaser? mine are squeakin all the time! hahahaa


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## jeff9nissan (Jan 9, 2004)

My AC does this too, but it also makes my brakes not work as well. So I don't use it for fear of not stopping... I guess it just gives me an excuse to do some engine mods :thumbup:


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## psuLemon (Apr 23, 2003)

jeff9nissan said:


> My AC does this too, but it also makes my brakes not work as well. So I don't use it for fear of not stopping... I guess it just gives me an excuse to do some engine mods :thumbup:


WTF are you talkin bout, since when does AC control stopping.


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## WiZzO (Jun 15, 2005)

be easy, i want to say he was joking...right??? omg what if he wasnt!! :jawdrop: lol


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## Ninety-Nine SE-L (May 5, 2002)

psuLemon said:


> WTF are you talkin bout, since when does AC control stopping.


it happens in my car too. The AC might bring the RPMs too low causing loss in the power brake assist. If you're idling below 500RPM and you mash the brake, there's a good chance the stopping power will be shit.


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## psuLemon (Apr 23, 2003)

Ninety-Nine SE-L said:


> it happens in my car too. The AC might bring the RPMs too low causing loss in the power brake assist. If you're idling below 500RPM and you mash the brake, there's a good chance the stopping power will be shit.


your braking and your AC are two whole different systems. Hell with a brand new car, if you just put it in neutral and try to use the brakes its goin to take more forces cuz you dont the gears helpin you out.. so if you have your AC on and you drop it in neutral try to stop. You shouldn't be at 500rpm if you have it in gear especially slowing down from a roll.


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## jeff9nissan (Jan 9, 2004)

Yeah, I'm never down by 500 rpm. But it does tend to stop worse with it on, consistantly, but mainly when the fan is on "4"


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## Ninety-Nine SE-L (May 5, 2002)

psuLemon said:


> your braking and your AC are two whole different systems. Hell with a brand new car, if you just put it in neutral and try to use the brakes its goin to take more forces cuz you dont the gears helpin you out.. so if you have your AC on and you drop it in neutral try to stop. You shouldn't be at 500rpm if you have it in gear especially slowing down from a roll.


ok, here's the deal. When you're about to come to a stop, turn off the ignition, and see how easy it is to brake. You might get some left over vacuum, but after that, it'll take almost everything you got to stop the car.

If you had cams, you'd understand what it's like to have no braking power. At idle, there's almost NO velocity in the intake manifold. No vacuum = no power brakes. Now, my car is set to idle at 1100RPM, I usually keep it in the 900-1100 range b/c EVERY TIME I push in the clutch or turn on the AC, the idle dips down to about 300RPM for about a second or 2. In the usual case that I push in the clutch and brake at the same time, there's a chance that there will be no vacuum in the brake booster and it'll take 300% as much effort to get the car to stop. I've scraped my crossmember MANY times pulling into parking spots.


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## psuLemon (Apr 23, 2003)

ok, but you having cams is a different story. You AC isn't what is giving you the problems, its the idle or the car. AC will make an idle raise. Now for a normal car without cams, there shouldn't be a problem with the AC except for the sluggish acceleration of the car athough a UR pulley will help minimize the affects of AC.. if the idles do drop that low, they need to adjust the idle screw and raise their idle. They should also think bout cleanin the iacv and the tb to smooth out the idle and maybe a good tune up.


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## nova73guy (Mar 30, 2004)

dam, shit's gettin' kinda deep in here. luckily I'm wearing my trusty flood pants, so only my shoes get messed up.


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## UofLsentra (May 25, 2003)

Just to add my $.02, sorry for the bump on this beaten horse.


About a month ago I drove from Elizabethtown, KY to Atlanta, GA on 10.5 gallons of gas (don't ask me why I can never seem to be able to put in the claimed 13 gallons in my car). I had the AC on almost the entire time (60% on 1, about 40% on 2) during this 5-6hr drive. I turned it off for about 30 minutes when it rained and I got cold, and for about 15 minutes of bumper to bumper traffic.

I drove my car approx. 70mph avg(maintaining RPM's and not speed while going uphill so as to not needlessly waste gas). I turn off the AC and stereo and all unneeded electrical when going up big hills. I drove exactly 402 miles into Norcross (part of Atlanta), GA and my needle was almost underneath the E line. I was on fumes. Then I topped it off when I exited to fill up 10.5 gallons.

My conclusion: With the AC on driving 70mph you get a little less than 39mpg. You might be able to get about 41mpg without the AC. Use it on the hwy all the time, no biggie. In bumper to bumper, ehhh. Let the people pass you up or just turn it on and off as needed to accelerate hard. Gas is too much to be speeding anyway.


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## himilefrontier (Jan 21, 2003)

I drive 500-1,000 miles a week (delivering pizza) and can't do without the A/C! What I do though is quickly cool down the car then turn down the fan so the compressor is not working as hard. I also have 5% tint in the back and 20% on the front windows to keep the car as cool as possible. Yeah, a GA with the A/C on is about as fast as a riding mower, but there are ways to mitigate the problem. P.S. I live in the Tampa Bay area of Florida and driving without the A/C is suicide!


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## B13boy (Dec 16, 2004)

A/C will rob you of power. If you want to go fast turn it off, if you want to be comfortable leave it on. Maybe at the stop light you could have the A/C on and when you see the light is about to change reach over and turn off the A/C till you are up to cruising speed then turn it back on. A/C on a 4cyl will make a slow car even slower, and a quick car slow.


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