I think we'll need a scientist to perform some tests.

But I don't care what anyone says. My Butt-Dyno is never wrong

I don't pretend to know anything about this, I just think they are too many obvious reasons as to why cooler air is better for performance. I definently agree with what tsXgtp stated. Its cooler air that helps, not nessesararly a cold day, although cold = cooler.

Why do cars on dyno's produce more HP when there's a fan blowing into the intake? or when the hood is up?

And why is'nt it called a "HAI" Hot air intake? I'm not disagreeing with anyones explanations. I just don't think anyone has really proven that its hot air that helps performance, and THAT was the topic of this coversation.

 

BZZZZZZZZ! I'm sorry, that was not the correct answer.

Since I started the conversation, that makes me an expert on what the topic is. And anyway you can check.

What we're talking about is if cars are faster or slower in warmer weather. That means ALL the factors that people are mentioning are relevant -- tires, plastic components, etc. -- not just cool air or warm air. The thing about cooler air vs. warmer air is just one of many factors. Of course I didn't know any of this when we started. But I did have a pretty strong suspicion that the cooler-air thing was just one piece of the puzzle, and it is. I don't think most of us (if any) know for sure yet how all these things balance out.

I like your "Butt-Dyno" criterion. And you know what mine says -- better performance in warmer weather, in most instances. For the moment, I'm sticking with that.

 

As mentioned in several earlier posts, it is the oxygen content rather than the humidity which affects the power produced during combustion.

What you really want to maximize is the amount of oxygen you can cram into a cylinder. The amount of oxygen n in the cylinder of volume V is related to the partial pressure of oxygen P and temperature T via

n / V = P / (RT)

where R is a gas constant. (Fellow chemists --- yes, the ideal gas law provides a very good approximation of reality in this case.)

A 20-degree drop in temperature will increase n by about 4%. Changes in elevation will affect atmospheric pressure (and n indirectly) to a far greater extent than changes due to weather systems or relative humidity. (The partial pressure of water in the atmosphere is much lower than that of oxygen anyway.)

 

Ok I never factored in the entire car in my last post. I was thinking purely of engine power, which I'm certain is more with cooler air. Now how does that effect the rest of the car? I still bet a car is faster at 70 deg than it would be at 90 deg.

 

I didn't say "hotter," I said "warmer."

I guess I should have been more specific. Not that it matters, since I'm probably wrong anyway.

(Actually I was specific -- I gave exact temperatures to compare. But in the discussion of course we use general terms so it can get fuzzy.)

 

So a 20 deg drop produces 7% more oxygen which we know helps an engine develope more power.

Now how does that 20 deg drop affect tires/components? Will that 7% increase in oyegen be enough to overcome the fact that tires lose some grip due to the colder temp? Someone must know.

 

Well, yes and no. First off, I bet it depends on the tire. Then there's all the other things, which also may vary from car to car, and which are probably hard as hell to measure, and on which the lab measurements may not correlate very well with how it behaves in real life. Plus, I bet that a 20 degree drop will affect most of these factors differently at different temperature levels -- e.g. there would be a different amount of difference between 20 and 40 than between 60 and 80.

I don't mean that we can't figure out anything. In fact, what we're figuring out already is awfully interesting, ain't it? But I doubt anybody is going to be able to figure out an ultimate answer that applies to all cars, or even to any one given car.

The ultimate test would be just to test the given car at different conditions, and see how it does. And even then..... what about differences in the tuning of the car, what about whether the driver is having a good day or a bad day......

Let's keep doing all these things, and see where we wind up. But it looks to me like there's always going to be plenty of room for both of us to assert our "Butt-Dyno" judgment.

 

Well, Larchmont/troublemaker/Jerry Springer's first post mentions a temperature range:

If we restrict the discussion to OEM tires I doubt you'd see any loss of grip in going from 80 F to 60 F.

BTW, there's a subtle error in my post which I'll correct. A 20-degree drop on the Celsius scale translates to 7% more oxygen. A 20-degree drop on the Farenheit scale translates to 4% more oxygen.

 

Thanks for the correction, DNB. While indeed it's a subtle error, in this case I think it's a huge subtle error. When you said 7%, I was thinking that probably settles the question for the most part, because it would seem unlikely that any or all of the factors on the other side could overcome that. But 4%, I think we've got a horse race.

 

Let's use two modified cars as an example and established some conditions.

1. Two identical cars with turbocharged setup. One has an intercooler, one without.
2. Both cars is warmed up to operating temp.
3. Both cars will be racing side by side under the same outside temp and weather condition.
4. Both cars will do a burn out to heat up the tires prior to the race.
5. Both cars will be driven by equally qualifed drivers. Make it race drivers.

Which car do you think will go faster on the track?

 

The car with the intercooler will win, but I think we all agree (Larch too) that cooler air does indeed assist the engine in making more power. Now the question is, is the car faster or slower when the temperature drops? We're trying to figure out how warm/cold tires and the rest of the car are affected.

 

In the case of my 0-60 in 6.95 seconds it was -22c and my previous best was a 0-60 in 7.23 seconds when it was around +25c. That would mean my engine was sucking 14% more oxygen at -22 than it was at +25. I can see how this could make a considerable difference in times.

As far as tires are concerned, I had to do a lot of aggressive driving to put enough heat in them to get a good launch so there definitely is a loss of grip at lower temps.

 

The one with the "Type R" sticker, of course.

 

Of course Larch, we forgot all about Dan's times and operating temperatures. Was'nt Dan's post responsible for this one?

Case closed.......

 

This is great. The further we get into it, the more we see how many things are involved. And, I think, the closer we come to having an idea how it all balances out.

Not to digress, but.....

A lot of things are like this. My favorite one is how we are so quick to second-guess the manager or coach or whomever. They put in this quarterback instead of that one, or this pinch-hitter instead of that one, and we think we know better. There's usually a lot more involved than what we know. OK, back on topic Suppose it's cold, or windy, or the turf is choppy, or whatever, and one of the quarterbacks isn't thrown off as much by that. Or suppose one of the guys got more sleep the night before, and the other guy is hung over. Or one of the guys just had a fight with his wife AND his girlfriend, and what he's thinking about is not getting any tonight.

And those are the things we're trying to find out about cars.

 

:noob:

Larch wrong thread, your looking for the "4th and inches" thread

 

tire temp and engine temp do no balance things out. We have to assume that the car has had enough time to warm up to normal operating temperature. Once this happens all will be equal, in fact if anything it will be better in the winter since the engine coolant doesnt need to do as much.

As for tire temp, thats not a big issue either. Tires can warm up pretty easily and besides, traction will only really factor in launching from a dead stop. (although it will sligtly effect hard shifts).

In any case, even with all the negative factors of cold weather it just does not balance out, as is proven in one of my earlier posts where i refernce a drag racing website which states that 1/4 times at night will be faster than during the day.

(ina ddition, by seat of the pants i can tell you that any car i have owned seems to be quite a bit more slugging during heat waves, or very hot temperatures).

 

That's probably what made me think of that.

 

I wouldn't have thought something so simple would be complicated. But of course that's because it really isn't simple.

"From a dead stop" is exactly what we're mostly talking about, FDL.
Remember, what kicked this off was the discussion between Dom and me about 0-60.


BTW even if the tires are warmed up, the road isn't.

Also, about "heat waves" and "very hot temps," remember that I specifically said that's NOT what we're talking about.

I guess I made it sound like I meant the hotter the better, without limit. I didn't. What I meant was that the OPTIMAL temperature isn't a cold temp, it's a pretty warm temp. (I specified 80 degrees F.) But I never said the hotter the better.

 

fdl, have you been ban from using the internet at work?

 

Interesting. In drag racing, they use a term called "density altitude" to reference what affect the atmospheric conditions may be expected to have on a car. I know for a fact that this value can and does differ by two or three thousand feet between two given days depending on changes in the weather. If barometric pressure and humidity differences have a minimal affect compared to actual physical altitude, then I wonder what other variables they can be including to come up with this "reference" altitude value?

BTW - I don't doubt you for a second dnb. I'm really am just curious as to what the hell they could be using to calculate this value. I would think that the only variables you would have are temperature, atmospheric pressure, and humidity level.

 

Right.

Earlier on this thread (or maybe it was the "How fast is it" thread), I said that I would have thought that the higher-temperature-related thinning of the air would tend to offset the lower concentration of oxygen, even maybe completely cancel it out. This was quickly tossed aside, basically without explanation. I gave the example of how temperature and barometric pressure affect the flight of a baseball. If a baseball is affected, why not a car?

The reason there's less oxygen in warmer air is there's less AIR. And if there's less air, there's less air resistance. That's got to have an effect on how the car travels. Maybe it's really just minimal, as someone said -- but I don't think we've really dealt with this yet. The degree of decrease in oxygen is exactly equal to the degree of thinning of the air, which is why I would think that maybe these factors offset each other. But I can certainly see that it might not work that way.

 

Thanks for the informative post. I'm not a drag racer and had to go off and read up on "density altitude." So bear in mind that I might be overlooking some of the nuances or so-called "common knowledge" aspects of drag racing.

In any event, here's what I found: Density altitude is a function of temperature, relative humidity and pressure. The density altitude fluctuations you mention are probably more a function of temperature than the other two factors. To examine this assertion, I did some density altitude computations using an online calculator.

First, let's look at how the density altitude is affected by a 20-degree drop in temperature, while keeping humidity and pressure constant:

80 F, 70 % RH, 960 mbar = 3505 ft

60 F, 70 % RH, 960 mbar = 2079 ft

The difference is ~ 1400 ft.

On the other hand, a 20% drop in relative humidity, while keeping the other factors constant, leads to a much smaller difference of ~ 90 ft:

80 F, 70 % RH, 960 mbar = 3505 ft

80 F, 50 % RH, 960 mbar = 3412 ft

 

biker addressed this early in the thread. Any change in air resistance due to differences in air density will become significant only at high speeds.

 

DNB -- I didn't think that really "addressed" it.

 

Dear Readers:

Let us answer the question, "How much horsepower is needed to overcome the increase in air resistance caused by a temperature drop of 20 degrees Farenheit?" For this discussion let us confine our speeds to the 0 -- 60 mph range.

This article works out the power needed to overcome air resistance at various speeds for a late model Corvette. At 30 mph you need 1.2 hp; at 55 mph you need 7.1 hp.

Now, if you look at his equations you'll see that the power P is ultimately related to the velocity v and air density d by

P = C d v^3

where C is some constant. The important point here is that P is directly proportional to d. For a given velocity, a 4% increase in d requires a corresponding 4% increase in P.

You know where this is going, don't you?

A 20 degree drop on the Farenheit scale increases the air density by ~ 4%. So at 30 mph you need an additional (1.2 * 0.04) = 0.05 hp to overcome the resistance due to the increase in air density. At 55 mph you need (7.1 * 0.04) = 0.3 more horsepower.

These incremental horsepower requirements are insignificant.

 

I have been out of town for work the past 2 weeks. I dont have much time to get on here.

I'm glad to be away from those freezing temperatures in Toronto though! ... although I bet my TSX would be super fast

 

It will be -40C with the windchill tonight !!!!

I ran a 5.4 sec 0-60 this morning on the way to work. Beat that Larch.

 

I'd say that addresses it.

 

Bench Racing: The act of sitting on your can and talking about motorsports.

I'd say this fully qualifies as "bench engineering."

 

Yup.

We've got bench engineers.

We've got magazine racers.

And our timeslips are old Sunday papers...

(Sounds like that song by Toby Keith.)