mbeguy

Okay,
I know this is a weird sort of question but I figure if anyone would know the answer it will be within this group.

Things I have heard (not positive they are true):
1. The ambient air temperature (summer of 100° vs winter of 50°C) effects the amount of air pulled into the engine and causes variations in horsepower.

First...is this true?
Second...if true, are we talking about a 3 hp change or 30 hp change?
Third...would the effects alter a 4, 6, or 8 cyclinder engine more?
Fourth...does humidity/altitude have an effect also?

2. The use of AC reduces the amount of HP available and acceleration of the car.

First...is this true?
Second...if true, are we talking about a 3 hp change or 30 hp change?
Third...would the effects be less noticable for a 4, 6, or 8 cyclinder engine?

Thanks for the education,
MBEGuy

gibbsy1

I can't answer your question, but I'm assuming you mean degrees Fahrenheit (F) and not Celsius (C). That would be a pretty damn hot summer and winter!

Sorry, but I had to post.

Intrepid

An engine will definitely generate more HP at 30 degrees than at 100 degrees. Cold air is more dense, which is why turbos use intercoolers. How much HP increase? I don't know exactly, but it is noticeable.

MaximumHP

iTrader: (1)

First:
Simplifying things a bit, there is only two things that create combustion. Oxygen and fuel. The fuel is where the energy is trapped, and to get it out it must be mixed with the correct amount of Oxygen to burn efficiently and create horsepower. In general if the ratio of gas to Oxygen is not exact the excess of either is useless.

When the engine sucks in air it gets what it gets like it or not. Not all air is physically the same! Air expands when heated (sometimes we microwave cold basketballs in the winter to expand the air inside to "pump it up") That means per physical volume, there is less oxygen. So if you suck in 3.5 liters of hot air there is less oxygen than 3.5 liters of cold air.

Second:
This means yes, you will make less power with warmer air. This is why intercoolers are used on turbos. How much power difference could result in an extremely large answer. depends on how much temperature difference, from what temperature to what. It's hard to say I'm wild guessing 5-10 HP in general (I really have no idea, there is probably something on the net about power vs temperature change)

Third:
The effect is linear depending on displacement.

Fourth:
The air is thinner at high altitudes, so yes. Formula 1 cars can lose as much as 50 HP at high altitude locations

Not positive on this one, I think the fuel mixes better with drier air?

cool dense air is the most desirable

Question 2:
First:
Air conditioning is parasitic power, as in it uses power for the AC that could be used for acceleration.

Second and Third:
A specific AC compressor will require the same amount of HP on all cars to operate. Using it on a Corvette will only use a small percentage of HP. Using the same unit on a Metro may take half your HP.

Not sure how much power you gain with AC off, someone else probably has a better idea. I would guess 5-15 HP, maybe more.

Intrepid

Most cars switch the AC compressor off at WOT (wide open throttle).

mbeguy

Thanks for the very good explanations. This is the type of basics I was looking for. I am sure someone has more precise details, but I am guessing they would be wasted on myself.

MBEGuy

rai

I agree with your post except the guess of HP (5-10hp = 2-3% gain), I think you are underestimating the effect. It is probably a percentage thing. So I think its 10% difference(between summer and winter) if you have a 100 hp car it may be 10 hp, if you have a 300 hp car it is 30 hp. I am not sure of the actual number this is just a Guess, but it is very noticible to me when running my weak ford escort in the winter it feels much stronger. If it were only like 3% that would be like 2 hp for my escort and I don't think 2 hp would be noticable. I think the difference can be as much as 1 sec in the 1/4 mile for the Z.

This is why I am planning on a cold air intake for my Z I think this is the most bang for the buck.

Also the major car magazines have a formula to correct for temp and altitude, if they didn't the acceleration times would be all over the map and a G35 at sea level in the fall would be faster than a 350Z at a little altitude in the summer.

texlace

It's all a matter of air density. The more dense the air, the more power. That is why a turbo or super charger boosts power. Likewise if atmospheric condition create more dense air, you get more power.

These atmospherice condition that govern air density are:

Temperature: lower temp, more density

Humidity: less humidity, (more oxygen/less water) more density

Elavation: lower= more density

Liquiid Ice

i believe you lose 10hp when u have the A/C on...thats why i dont drive w/ it on unless i have my gf in the car, or is very very hot out.

MatthewZ

I've heard ~1hp for every 10 degrees F you drop the temperature of the air entering the engine.

John

iTrader: (17)

Heat will definitely drain power, but I'm unsure as to how much. Best example I can give is that a 90F day at the drag strip will usually yield times .5-.7sec slower. Don't forget that on a hot day, the heat on the road is going to be much greater, especially if it's asphault, and the air closer to the road (where the intake is), is going to be much hotter.

As for A/C drain, I'd say it robs your motor of about 15ft-lbs torque.

skimark

Living in Denver at 5,000+ feet of elevation I know you loose quite a bit of horsepower at high altitude. Our dragstrip - is at 6,200 feet and 1/4 mile times are usually 0.7-1.0 seconds longer.

jreiter

iTrader: (6)

I think there is a bit of a misunderstanding as to how so-called "cold air intakes" work. For the life of me I could never figure out why on Earth they are called cold air intakes. The air they suck in is not any cooler than the air the stock intake is sucking in. In fact, it's been my experience that in many cars the stock intake box allows for *lower* intake air temps than the aftermarket intakes.

Here's the deal: a stock intake box typically has some sort enclosed ducting that goes to the front of the car, sucking air in via the grill. This means it's getting air straight from outside the car. It's not going to get any cooler than that.

But now consider an aftermarket open-element intake. (what are incorrectly called "cold air intakes") It is sucking air straight in from the engine bay. This air is almost garanteed to be at least a little bit hotter than the outside air because you've got the engine pumping out huge amounts of heat. There are ways to improve this, such as rigging up some sort of do-it-yourself ducting from the grill in the front back to the cone intake. This can generally get the intake temps down to somewhere around outside temp.

However, the reason the open element intakes generally provide more power than stock intakes is because stock intakes create more air flow restriction. A stock intake is more restrictive because of any of the following:

1) They typically use basic paper filters. These are usually more restrictive than something like a K&N, which is an oil-coated cotton-type filter.

2) The intake box and ducting of the stock system is often designed to reduce intake noise, and this noise reduction often creates flow restriction.

3) The total amount of filter surface area of a stock system is generally less than on a cone intake filter. This means there's simply less area for air to flow through in a stock filter, and thus more flow restriction.


But the heat problem is the killer on open-element intakes inside of an engine bay. You almost always have to deal with that in some way. On an Audi A4, for example, the intake box is near the turbo. There is a huge amount of heat being generated by the turbo, and thus the stock intake box was designed to be well insulated against that heat. When you remove that intake box and stick an open element filter there, people often find that they are actually getting *less* power because their intake temps have increased dramatically! So the aftermarket intakes, at least for Audis, usually involve some sort of fancy duct work and heat shield.

So you should always check your intake air temperatures before and after the installation of an open element intake inside your engine bay. It's possible that your intake temps will be higher, but since you're getting more air, that offsets the increase in temp. (sometimes... but not always!)
-joe

rai

I'm not sure if you are a mechanic or what, but I was under the impression that the stock air intake is getting a hotter air mixture than if you put a true CAI, not some K&N air filter that you are talking about.

I tend to believe VQ racer on this, but if anyone else can give us a real answer it would be appreciated.

2003z

iTrader: (7)

A true cold air intake, relocates the air filter, or its pickup point to the outside of the engine bay, just like most stock units actually (at least their pickup points)

Stock units, usually just have a tiny hole to get the air in however. If the intake is in the engine compartment, its not a CAI, just an intake that flows much more air than stock, and even though its hot, its still better.

My 91ZX TT had an HKS twin cold air intake, just behind the front bumper, and my 00 323Ci, had a dinan CAI, which was just in front of the left front tire. In both cases, it was major work to remove the panels to get to the filter, but they provided true cold air, and a lot better flow.

2003z

iTrader: (7)

I just saw a CAI on Hi Rev tuners on Speedvision, I think AEM makes it, but it had a foam section in the engine compartment that would allow air in if the filter was submerged for some reason,

2003z

iTrader: (7)

You know, Victor, It took me many years to figure this stuff out. I wish I knew as much about this stuff when I was your age. Would have saved a lot of mis-steps.

rai

well you were backing me up first.

I am not any type of mechanic or tuner (before the Z), but I have a friend that is very knowlegable. The CAI may not be done at the factory for the theoretical reason that if you drive through deep water that water can get in the engine. Some people say this is really not the case unless you drive through like 2 feet of water.

TJZ

Yes, vqracer is right, sorry about the delay "backing you up"

FYI to everyone: "hot air intake" is also called SRI.

Injen claims some big hp gains with there SRI for the RSX-S. But some people at clubrsx.com have found out that once it heats up in the engine bay, its pretty much worthless. So a lot of people have been switching to CAI's.