SLY1TYPES

What is the deal with humidity and horsepower with our cars. When it is very humid my car feels like it looses a lot of horsepower. I really noticed it tonight (80 and humid as f*ck rained alot earlier today) when i raced a turbo eclipse and got smoked, and i have raced him when it was about 50 out and was pretty close. I have the icebox CAI, but is there anything i can do ????


Kevin

mattg

more moisture in the air means less oxygen and less hp.

typeR

more moisture(and heat) in the air means more heat retention in the heads causing the ECU to back off timing to curb detonation...80-20 mix of water coolant,redline water wetter and the mugen Tstat and fan switch will help some...

dfreder371

As a former Certified Flight Instructor, here is your answer:

HHHHH.

Or, High, Hot, Humid, and Heavy HURT performance. OK, you're gonna learn a lot about air here.

The international standard atmosphere is assumed to be 29.92 inches of mercury and the temperature is 59 farenheight at sea level. It also assumes that the pressure drops one inch and the temperature decreases 2C (3.5 farenheight) for each increase of 1,000 feet of altitude above sea level. This is one reason that "cheap" airplanes (less than $1,000,000) do not have air conditioners. Just fly higher. It will get cool enough, soon enough. BTW, you would be suprised how little $1,000,000 can buy you in avaition. Flying is not cheap.

Anyway, HIGH: Air is thinner (less molecules of the stuff) at Leadville, Co, elevation 9,927 ft, vs. Miami, about 10 feet. At leadville, the ground roll for take off will be aproximately twice that at Miami.

HOT: The air thins out when it is hot. Under winter conditions, a fully loaded 747 can leave the ground in about 4,500 feet of ground roll. At 85 f, it is more like 8,500-9,000 feet.

HUMID: Here is the one that fools almost everyone. When it is foggy out, everybody says "the air is so thick, you could cut it with a knife." Dead wrong! Clean air is made up mostly of Nitrogen, N2, and Oxygen, O2. The atomic weights of air is essentially (99% of it) (N=16x2+O=18x2), or=68. When it is foggy out, The N2 and O2 get displaced by water vapor, H20. H20= (H=1x2+O=18x1)=20. So there, in a nutshell is your explanation! The air is actually THINNER! By more then three times!

HEAVY: Naturally, carrying around a trunk full of anvils in either a car or an airplane is gonna hurt performance.

I think I have sucessfully answered your question

Nashua_Night_Hawk

use this: http://wahiduddin.net/calc/calc_hp_abs.htm

r10apple

I feel like we're in a class at MIT...
Don't feel bad, Sly. You could live here in fu(king Florida where an auto TL-S spins madly hitting second in the winter, and yields a scant yelp from March to November (except first thing in the morning)...

ChucksTL_RENAMED

And I'd like to add that for every ten degree increase in air temperature causes a loss of 1% of your horsepower! Nice work dfreder370, thanks.

allmotor_2000

Good job dfreder370...!!

Nashua_Night_Hawk

Example:

50F, 30.5" AP, 20% RH == 108.1% Relative Performance
85F, 29.5" AP, 90% RH == 095.8% Relative Performance

There is a difference of 13% due to weather alone.

dajuice27

DAMN!!!!!!

So what he means is we will go slower!

Wires

The only real cure is getting boost. (That's why he killed you).

All N/A cars perform the same.

SLY1TYPES

thanks!! for the awsome explanation defreder370, This is my first N/A car, my old car was a Grand Prix GTP 3.8w/supercharger and i would never really notice the loss of power with humidity.

Kevin

dfreder371

Appreciated, guys! If you are going to fool around with things as potentially dangerous as airplanes, it pays to know ALL about the media you are swimming in.

Airplanes are like cars, or I suppose, guns. They all are safe. It depends upon who is operating them.

People take air for granted. They think it is not there. The appropriate way to think about it is that you live on the bottom of an ocean of air, just like a lobster lives on the bottom of an ocean of water. And, for further education, why do jet liners fly so, so high? Answer: Turbojet engines are absolute fuel hogs the lower they go, due to the density of the air.

And, this is also the appropriate thread to explain why fuel injection is so superior to carbeuration. With a carb, there is an opening of a given, fixed area that is controlled by a plate. The plate can almost choke it off (if it did, completely, the car would die), or it can be "wide open", or parallel to the air flowing through it. This offers very little resistance. Either way, all the throttle valve in a carb does is govern the VOLUME of air passing. It is blind to temperature, air pressure, and humidity.

FI, on the other hand can be described thusly: Imagine a 3 inch circurlar hole for air to pass through. Inside that hole is a 2.995" circular clate that is centered in the bore. The .005" clearance is there to allow the engine to idle. The plate is connected to a lever, on which the opposite end, the fuel flow is controlled. Inbetween the two is a fulcrum, a "pivot point". Now, all the variables are under control. Lower or higher than "standard" air pressure (density) is factored in, so are also, non standard temperatures, either higher or lower. High humidity is a defacto, "low pressure" factor. Fi doesn't recognize nor measure the humidity, but it falls under the density factor.

So, you see, the best power combination of low temperature air and high atmospheric pressure pushes the plate down farther, and allows more fuel to flow. Conversely, whe it is 110f out, and the pressure is low, the plate is not depressed so much, and allows the proper mixture. Mix the two up, high temperature, and low pressure, or low temperature and high pressure, the results are the same. What needs to be measured here is the FORCE of the air. Glad to help, and thanks for the nice compliments again! In winter, the temperature is low, and the air density is usually high. This is why your gas mileage goes down in winter. No mystery here.

darrinb

thats y i hate the track when its over 65 deg

6speedctrlfreak

I have noticed that during the first 6 months ( about 3K mileage) my '03 CL-S perform a bit sluggish when the temp was above 65 dgrs. ...but now after my first oil & filter change last month It seems to run stronger in all types of weather (humidity and temp.)

Zapata

:bubbarubb