Guest

I've read and understand the logic of the mechanics behind pulling the AC fuse & then running the car A/C ON to gain a little extra power. Has anyone ever seen or performed any sort of quantitative tests to conclude wether or not this is a tall tale or really works? Just wondering since winter is right around the corner : O .

Turbo95Max

iTrader: (25)

how will this mod give power? im wondering where the logic is...lemme know, later

Che

how does that add power??

breaux124

iTrader: (1)

How can removing the AC fuse and then turning the AC on, increase hp? Removing the fuse would just break the circuit to the AC and not allow it to turn on. So without the fuse, it wouldn't matter if the AC was on or off, the car wouldn't know the difference. Maybe I'm missing something here ... could you give a brief explanation of the logic.

Bryan
1997 SE - not stock anymore

Guest

>>tech knowledge than I (which wouldn't take much) can prolly better answer these inquiries, but, the basic premise is that the stock ECU is engineered such that it senses when the AC it turned on and adjusts engine settings so that the driver does not experience the typical loss of power which occurs in most cars when driven AC ON. Pulling the fuse prevents the signal from getting to the compressor, thus you're really not "AC ON", but, the ECU doesn't know that, so it adjusts the engine power output up a few ticks to compensate for what it believes is an AC ON condition. If you recall the thread in which several experienced track guys gave Chebosto advice for Button Willow, this "mod" was advised by someone, Nabil I think.

I'm sure that I've screwed up this explanation in some fashion or another, but hopefully you get the idea. Don(inTexas), Jeff92Se, etc.. if one of you guys is out there, can you please elaborate?

Shingles

Although this might sound like a good thing or a right thing... I don't think the ecu adjusts the engine performance when the ac is on. Fact is, if this was the case, the ecu wouldn't ahve to disengage the compressor when AC is on and you are at WOT. I believe pretty much all of the power lose associated with AC is the parasitic<sp?> lose when the compresoor is engaged. So as long as the AC compressor in not engaged, you won't feel the power lose.

-Shing

Keven97SE

I've always noticed that my car runs as well if not STRONGER with the A/C on. Totally against what I'd expect. I wonder if Nissan programmed more aggressive ignition timing maps and/or fuel maps for part-throttle running with the A/C on. I know the compressor turn off under WOT but I would think Nissan didn't "skimp" on the ECU maps under no A/C just so that with the A/C on, the car feels the same. They turn off the A/C under WOT so that you keep the same power level...but under part throttle, they have some room to play with, and they tried to adjust things so that A/C and non-A/C power feels approximately the same.

Of course, if this trick does work as intended, there will be no WOT power boost (read: you won't dyno more power or accelerate any faster), but part-throttle driving could be more lively.

Hmmm, I'm gonna try this.

Thanks, Booker!

Guest

No prob Kev., I KNOW that some guys have posted a more tech description of this set up & I hope they come here and post. More aggressive ignition timing maps seems to make sense, but I don't know that much about the science. I KNOW that some guys have posted on this topic in the recent past. I'll look for the Chebosto/Button Willow thread & see if I can dig up the dirt.

Shingles

hrmm.. interesting... who knows, I'll give it a try too.. but I'll be in and out of the country for the next 4-6 months... so I may not have a chance to do so.... we'll see.

-shing

Turbo95Max

iTrader: (25)

im not sure about more aggressive ignition and timing maps but the Compressor is free running. Meaning it wont drain any power when the engine is driving the compressor as long as its not engaged. When engaged, the ECU is suppose to higher the idle cause of more load on the motor.

Guest

http://forums.maxima.org/showthread.phtml?threadid=348


Some other racing hints & tidbits
In addition to what Biomax said, you could remove the A/C fuse from the fusebox and run the car on the track with the A/C turned on. You won't get any cold air because the compressor itself won't engage, but the ECU will be operating with its heavy load maps and operate the radiator fans sooner and longer and run a slightly richer mix of fuel.
Kudos to Hiroshi for that hint.

Another one is to learn to look ahead to the next turn and not narrowly focus on the front of the car, and you'll be better positioned to negotiate the turns.

The Maxima is one nose-heavy car that can literally plow off the paved track if throttle is not judiciously applied when coming out of the turns.

Use wheel chocks instead of the hand brake in between sessions.

open the hood between sessions and let the engine vent.

Refrain from beating up on the Civic SI over and over in every session even though he refuses to believe that the Maxima can lap him quite easily.. lol (j/k) ;-P

Most of all though, the best attitude to have is one of learning and sharing your knowledge and racing techniques and lines. And that's what makes road racing so much more fun than drag racing.

This Saturday @ Buttonwillow will hopefully be just as much fun as before. http://www.buttonwillowraceway.com

--Nabil




Anyone know who this "Hiroshi" is?? Maybe that's the person who can clue us all in, has done some form of quantitive testing & can give us his (her?) findings. Someone get Nabil in here. He seems to spend a lot of time at & on tracks and knows a lot about performance driving.

RussMaxManiac

My 2k's AC never shut off when floored, neither did my 98 SE.

Guest

Which brings me back to my original post & the reason for this thread...does anybody really know?? I will say this, Keven has a good point, in that power loss with the AC on, is virtually indetectable in my Maxima. It is the first and ONLY car I've ever owned which can make this claim. Either it has the world's most efficient compressor, or the engine is compensating in some fashion for the parasitic loss. No so unreasonable to presume the latter to be true. If it is true, this compensation and the killing of the compressor at WOT are not necessarily mutually exclusive facts. I don't think you can say that, "if this was the case, the ecu wouldn't ahve to disengage the compressor when AC is on and you are at WOT". Why not? Pressing the throttle to say 85% of full open could well trip a trigger as a safety design. Say a person is crossing Arizona in the middle of the day in the middle of July. Its 105 out, so naturally the AC is on. You're cruising at 75 MPH so the car is in overdrive. For some sudden reason you need to mash the accelerator to the floor in order to get around that slow moving truck..... Perfectly reasonable to asssume that Nissan would so map the ECU that it kills the compressor until a more normal throttle setting is returned.

jgadlage

iTrader: (1)

go for a drive and report back what they find out. It really isn't that hard to do instead of wasting time arguing about whether or not it would work. I would but I am stuck in work right now.

Guest

I don't really think there's any arguing going on here, just guys expressing what they think based on their particular knowledge and experience level. No foul there. And I certainly wouldn't call the discussion a waste of time, at least not for me personally. I've learned more about ECU mapping in this thread than I knew before. That's the beauty of Maxima.org, baby!

A yank and a drive would help, but is not definitive. What I'd really like to see/know is if someone is going to a track anytime soon, make a couple of runs with and a couple without. If pulling that fuse all of a sudden gets EricL's stock 97 GXE auto down to 14.2 - I'm IN!!

Shingles

Well maybe cause we too are at work. No one is "arguing" we are discussion about the possiblities...

hodgeee

It does have the computer bump the vacuum. This in turn jumps the idle speed by about 250 to 350 rpm, to make up for the parasitic loss of the drag on the AC compressor. No it does not bump up the fuel injector mapping or such. This is an old fable that we used to tell the new kids at the drag strip. There have been many people that we knew that would go to great lengths to see if this would work, but only ran the same numbers as before.

For four years, this was heard everywhere you went. I believe someone speculated it, someone else relized how funny and stupid that was, and then everyone spreaded it.

Urban Legend!

Nismo87SE

Actually its because your Idle up soliend has a load on it. The ECU uses it to increase the idle to make up for the parasitic loss of the AC compressor when its engaged. Also if you were to leave this fast idle control on it "might" flow more air into the manifold but would it make a difference. Besides the ECU cuts off the fast idle control at a certain rpm.

Matt93SE

iTrader: (44)

richening the mix and leaving the radiator fans on will simply create cooler running conditions for the engine, thus it SHOULD produce more power since it's running cooler.


some people have said that they don't notice any power difference between A/C off and A/C on, but I have noticed there's a pretty obvious difference while driving in the city. the engine is more "sluggish" then without ac on.. that could be because of the higher load on the engine causing it not to respond as quickly (yet still putting as much power to the wheels), but then again it could be causing a real power loss and the ECU isn't compensating at all.
I dunno.

the idea sounds like a good one, but I dunno if it'll work or not. I'll pull my fuse on the way to my other job in a few minutes and post my findings tonight.

well, maybe not.. it's 95+ outside today.. I'll THINK about pulling the fuse!

Guest

Could also be that 3rd and 4th gen ECU's are radically different in this particular area. In my 4th gen, you can BARELY tell the difference between AC ON and OFF in race mode type driving, in everyday driving you simply cannot tell that the AC is on. The car has absolutely none of the sluggishness that it sounds like yours does.

Keven97SE

I don't know if that's true on these "newfangled cars", old one

SAAB advertises some sort of "smart" A/C that does EXACTLY what I said. They designed it such that there is no difference in power between the A/C being off or on.

What do you say to that, Mr. Smartypants?

Just kidding, I'm just trying to state that if SAAB is doing this on their cars, it's possible Nissan is doing it to the Maxima. Either that or like Booker said, this is one efficient A/C because there's almost no power loss with it on. My car actually has slightly BETTER power with it ON.

And FYI, there's an A/C throttle bypass solenoid located next to the idle solenoid (AAC is it?) that opens wide during A/C operation to add more air to the engine during A/C operation. That may pose some funky high-idle problems during my "fuse test" tonight.

Nismo87SE

You guys are telling me that you don't really notice a difference when the AC on as opposed to when its off? WTF? I can feel the power loss when the AC is on in my car and the power gain once I turn it off. Especially when I had the UDP you can really tell when the AC is on. But then again my ECU is like the 486 processor compared to the ECU's in the 4th gens. Maybe I should go out and test drive a 4th/5th gen to see if I can feel if the AC is on or off (power loss wise that is).

RussMaxManiac

I remember someone a while back saying when he had the AC on at the drag strip with his SUPERCHARGER his car ran STRONGER with it on! Now at times my car has felt stronger with the AC on instead of OFF.

RussMaxManiac

Yeah Nismo but you have 2 generations back of technology. We are talking really about the VQ. My SE-R drags with the AC on, same goes for the new 2k Sentra. All my maximas you could not tell when the ac was on or off, sometimes I forgot to turn it off in a race. BUT, I remember a race a long time ago, in my 98 Maxima, I ran this guy twice, I FORGOT to turn the AC off, it was agaist a MODDED 240SX 98 model, he was very quick and ran mid to high 15s. Well anyways, I did not beat him till at least 75+ mph to pass him the first run. The 2nd run I asked him to go again since I left the AC on, I turned it off, this time same lanch, but I pulled right off the line and passed him by 45mph. So I could tell there it made a difference, but sometimes the cars feel stronger with the AC on then off.

Chebosto

iTrader: (1)

By pulling out the fuse and turn the ac on, you fool the computer thinking that the AC is turned on..
BUT. when the fuse is out, the ac unit never turns on, but it keeps all the fans turning, sucking in more air into the car, and giving you car, not necessarily more power, but freeing up the power used by the ac unit, for other parts of the car.

i used it during ButtonWillow, along with Nabil, and Hiroshi. worked great. it made the engine bay a bit cooler, since it kept the internal fans blowing/sucking. (;P)

but the gains aren't that great. it's just a little something to get some more goodie juice.

sprung

I'm sorry but some of you guys are really clutching at straws thinking that your A/C fuse is a mod!! Everyone needs to stop and think about this for a minute...Okay now if the motor makes more power with a different ECU map when the A/C is on WHY wouldn't car manufacturers use that map ALL the time!!! Do you really think they are holding something back just so you can't tell when the A/C is on? Come on...the reason you can't feel a difference is b/c the VQ makes more than enough power for the Max. An A/C compressor gives basically the same hp loss to every motor you just FEEL it more on one with less hp b/c it's losing a greater % of it's power.

I have an idea where this rumor came from, a LONG time ago I was reading a Honda page that had some one's suggestion about what to do at the track (Honda's need this kind of help). This kid said that track officials will ask you to leave if you run your A/C and drip water on the track. He suggested pulling the fuse and turning on the A/C after you run. This way the 2nd electric fan that goes on for the A/C condenser will help cool your motor between runs without making a mess of the track.

Guest

That explanation makes sense, more whirling fans = more cooler air getting into the engine compartment = a better running engine. BUT, it is somewhat inconsistent with what Nabil posted to you last week. Nabil, to my understanding, is a quite respected, knowledgable guy about cars in general & Maxima's in specific, and he plainly stated that pulling the fuse & running AC ON "fools" the ECU and causes it to runs its more aggressive maps. I'm STILL trying to find out if this is true. After an entire day of back & forth, I think it safe to say that no one really knows for certain one way or the other. Except for someone (Nismo - ?, can't recall right now) who did say that its an urban legend, of sorts.

sprung

I'm gonna have to agree w/ nismo..? on the urban legend explanation. There's ALOT of mis-information out there in cyberspace, just keep in mind the old saying..."believe half of what you see and none of what you hear."

Che

i have never really noticed any power loss with my ac on either, i'm in oklahoma so it's hot and i drive with a/c on everywhere. on the occasional bearable night, i may turn it off while driving and open windows. but i feel no gain in power. the last time i went to the track, i had my a/c on while running. ran a little slower et of 15.3 as opposed to 15.1 without a/c. loss of power...maybe. it could just be a fluke. or lousy driving....who knows...anyway, just my .02

Shingles

Ermm the idea behind this different map is so you won't feel the difference between when ac is on and off, when you "use this map all the time", kinda defeat the purpose no?

Keven97SE

It didn't do jack.

Sorry guys, I didn't notice any difference.

So much for the theory.

Guest

Less than scientific, but a step in the right direction.

Let me claify the point. Suppose pulling the fuse really can causes a car which typically runs a 15.5, to be able to run 15.41. As anyone w/track experience knows, this is a significant gain in power, yet, one that is not likely to be detectable by a "seat of the pants" comparision against your memory of the last time you drove the car.

I think I'll accept that its folklore for now, unless Hiroshi or someone w/real tech knowledge and testing comes in and refutes.




[Edited by Booker on 09-08-2000 at 02:58 PM]

Dave B

I can notice a bit of difference with the A/C on in my modded 96 Max. Maybe it's because I rarely run my A/C unless I've got people with or it's 90 degrees outside. I hate driving around town with the A/C. I would never recommend racing with the A/C on because your spinning the compressor WAY TOO fast and you'll eventaully kill it. I don't know why Nissan cut corners and didn't put a compressor clutch in the A/C. My Z28's A/C would shutoff at 4000 rpms or WOT. It was a great setup and saved your compressor.

About this A/C mod. I think it might be a good thing for the 1/4 mile track. However, you must remember that the power required to run the fans will take hp away from the car. Also, no matter how cool your engine is, if the weather is hot and humid the hp is gonna suffer. You can never expect good times out of your car in 80+ degree weather with high humidity. No CAI can make up the difference either since the ambient air off the pavement is 120 degees.

As for the ECU going into some kind of "aggressive" program, I'd disagree. The engine idle is raised to compensate for compressor drag. If it didn't do this the engine would vibrate because idle would be around 500 rpms. And I'll say it again, my car is definately slower with the A/C on. ALL ACCESSSORIES SHOULD BE OFF AT THE TRACK. I'm talking your headlights (unless required), stereo, heater, A/C, blower fan, radar detector, etc.

Dave

hodgeee

I think the biggest reason that people don't notice a difference is the way they drive. You have your a/c on when its hot out during the day, and then you turn off your a/c when it is cool at night. For every 10 degrees over 72 degrees, in the old racing book, it accounts to 2 to 3% loss in horsepower. How many times have you noticed how the car feels slower or weak during the summer time, and better at winter. The cooler the outside temperature, the less the a/c compressor is actually activated or engaged where it is dragging on the motor. At night when it is cool outside, it is possible that your a/c compressor is not working hard as it would during an 110 degree day. This makes it much less noticable. I even notice this out here, during the night time when it cools off, I cannot feel the difference in power. The average driver usually cannot tell the difference in power unless there is about a .2 second improvement on the car. Most cars evaporator systems are very well designed now a days and it takes much less power for a compressor to make the cold air. In some cars I can feel a huge difference when the a/c is turned on, and in some cars, I cannot feel a difference. I remember in all my pre 90 cars, there was a great noticable difference in power with the a/c on. But then again, I remember my a/c used to really kick out the cool, and none of the after 90 vehicles I have had, ever put out the same chilling air. But then again, some people do not notice little things like this any way you try it. My last girlfriend could feel no difference in the power of my Max from when it was stock, to after I modded it. It is running .4 seconds faster in the 1/4, and feels much faster to me. She used to drive my car quite a bit, and can't notice any difference, same for my brother.

Now a lot of people will even say that it feels like the car has more power when the a/c is on. They can get this, due to the fact that the motor is actually running at a higher rpm, and is adding slightly more throttle. If they are in an environment that is relatively not too hot compared to like in Vegas or Arizona during the summer, then when they step on the gas it feels like the car has a little more jump. Which it actually does, because it is running the motor at a tad greater throttle, or higher idle. So now when you first step on the gas half way, you are actually giving it more than half throttle, due to the bumped timing or rpm raise or throttle bump. I have never heard anyone in the summer time here in Vegas tell me, they did not notice a power drop off when the a/c was on in the heat. Due to the fact that when it is cooler out, the freeon in your car is allready more compressed, so the compressor does not work as hard, actually putting on less parasitic drag.

Now I know some people will say that they can feel no difference out in Arizona or Nevada, but I say those people must have slow signals transferring to their brains and wouldn't feel a difference in performance between a camaro v6 to a camaro v8. My dad is that way! He says that his 98 corvette feels no faster than his automatic 88 mustang gt. I even ran his old mustang at a drag strip and it would barely break into the 16s. He drove a 13.8 himself three months ago at Las Vegas Speedway, but I still can't get him to believe that the best his old car would do was 16.9. Unless he drove it himself he said that maybe his Mustang would do 14.0 flat at the track!

Hell I guess in this post, I am defending the ones who don't know better as much as the ones that know what I am talking about, except for the end here!

ZuMBLe

iTrader: (1)

I would have to agree with you. I have a 4th gen and I can tell when the A/C is on. This may be because I have an auto. The tranny seems to not want to downshift when the A/C is on. During highway driving its not as noticable. But in the city.. I know its there.

ZuM

Nabil

OK... I just checked my email to notice something from Booker telling me to come over and add my $0.02 worth to this "Speculation Skillet™ " ;-P

OK... I never claimed extra horsepower, and contrary to what people are thinking, this AC fuse pull thing just helps put the car under "heavy load" operation that the ECU already has to compensate for the abuse a track outing would exact on the car.

Running under these conditions, the ECU would run the cooling system more aggressively to cool the engine. It also runs the fuel maps slightly richer to avoid pinging.
We first got wind of this when Stillen was demoing their SC car back in 98 and they had the AC on. We wondered about it and they mentioned the richer fuel maps. The cooling fans are also a good plus in extreme conditions like running at the track.

I hope this clears up the skillet for this time. ;-)

--Nabil

Nabil

If you want to discuss this with me further, please do it at http://clubs.yahoo.com/clubs/nissanmaxima since I hardly ever come here.

Regards,

--Nabil

Guest

Eric L.

Hey, WHOSE Maxima are you calling STOCK????

You're just a hater like the rest of em...heh