Weather Theory
10-22-2012, 05:27 PM
#1
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Weather Theory I guess you can call this a tech thread but my buddy tried to argue with me about being in colder climates can have a power advantage. Could winter cars put out more power then a hot florida summer day? I also wondered this. I do notice my car has a little more kick to it after 5 mins on a cold start then it does when its been runned for over an hour. Its a newbie type question but a good one.
10-22-2012, 06:09 PM
#2
Of course, it puts out more power on a colder day, all other parameters being equal.
Most closely described by the Ideal Gas Law: PV = nRT
Never mind about n and R; they're constants as long as we're sticking with air.
For an N/A setup:
P = atmospheric pressure
V = the volume of air ingested on the intake stroke
T = atmospheric temperature
As T increases, V increases, so at higher temperatures, each cylinder full of mixture contains less oxygen molecules. Less oxygen = less possible burn.
A very simplified explanation, hope it helps.
Most closely described by the Ideal Gas Law: PV = nRT
Never mind about n and R; they're constants as long as we're sticking with air.
For an N/A setup:
P = atmospheric pressure
V = the volume of air ingested on the intake stroke
T = atmospheric temperature
As T increases, V increases, so at higher temperatures, each cylinder full of mixture contains less oxygen molecules. Less oxygen = less possible burn.
A very simplified explanation, hope it helps.
10-23-2012, 07:33 AM
#4
what those guys up there said..............in the drag racing world the MAIN thing to look at is Density Altitude which is the relative measure of air density and water grains........as a rule of thumb 1000ft of da is worth .1 second and 1 mph.......this in fact does work perfectly on my car ive been doing my calcs all year......
10-23-2012, 08:07 AM
#7
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It's not a theory. It's complete fact. For extreme sake, drive around Denver and then head east or south and you'll noticeably feel a difference. Of course it depends on where it is cool. If it's 20* yet you are at 10,000ft ele you'd be better off at zero ele on a 100 degree day for reasons already stated.
Texas Motorplex is around 700ft. ele. Best I ran there stock in nice weather was a 13.9 @ 100 while sitting and letting the car cool down. Went down to Houston Raceway Park which is around 15ft. ele and ran a best of 13.6 @ 102 and hotlapped consistent 13.9's.
Less extreme is try running your car at the track at full operating temp and then completely cool. You will see a vast difference. You'll see it on the dyno too. At least 10 to 15rwhp between operating temps and completely cooled down.
Texas Motorplex is around 700ft. ele. Best I ran there stock in nice weather was a 13.9 @ 100 while sitting and letting the car cool down. Went down to Houston Raceway Park which is around 15ft. ele and ran a best of 13.6 @ 102 and hotlapped consistent 13.9's.
Less extreme is try running your car at the track at full operating temp and then completely cool. You will see a vast difference. You'll see it on the dyno too. At least 10 to 15rwhp between operating temps and completely cooled down.
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10-23-2012, 12:25 PM
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But thanks for the good info. 
10-23-2012, 01:09 PM
#14
You posted an excellent question. A lot of people overlook atmospheric conditions when they are making a performance comparison. Another good point brought up here was engine temperature (especially intake temp.).
We check our weather station after every run and make fuel adjustments as necessary.
10-23-2012, 05:05 PM
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Woops guys. lol excuse me for the misunderstanding. I just figured the 130mph friend was me because of all the people bashing me in the old thread haha but anyways good info thanks. I wonder how cars perform in the winter in Alaska? -32. From stock & from factory what is the temperature of the air tested? Im assuming room temperature. Im also assuming the colder the air the less fuel?! I know here in florida my car sprays more fuel in the hot summer days to prevent it from overheating & detonating. I heard the PCM was tuned to from factory to adjust fuel on temperature of the engine.
10-23-2012, 06:39 PM
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The ICAO International Standard Atmosphere standard conditions for zero density altitude are 0 meters (0 feet) altitude, 15 deg C (59 deg F) air temp, 1013.25 mb (29.921 in Hg) pressure and 0 % relative humidity ( absolute zero dew point). The standard sea level air density is 1.225 kg/m3 (0.002378 slugs/ft3).
10-24-2012, 01:16 PM
#17
Try driving a forced inducted car, then you will know a bigger difference between the seasons...I went from 648 RWHP on a nice cool good DA weather and with no other changes, summer came, DA was bad and the car made 536 RWHP, This is power you can feel you lost...
10-24-2012, 01:40 PM
#18
moehorsepower knows what he is talking about and I am not questioning his result. I just feel it important to note for the newb who started the thread.
Dynos are generally setup to correct the output numbers for weather conditions, this is why you sometimes see STD or SAE correction factors listed on dyno graphs. So in theory you should be able to dyno a car in Alaska outdoors at sealevel under high pressure in January and get the same treading as a 90 degree day in Dever or a 100 degree day in Vegas or whatever.
Often though tuning is not optimized across all weather conditions though and the output number will change.
There was a time when my car There was a time when my car lost a solid .6-7 from weather alone, what I found was the tuner I had used had halfassed the tune and had not changed some of the temperature vs. spark tables and in the hot weather it read a little knock and pulled a bunch of timing reducing power even more than what the over 100degree temps and high humidity were doing for me..
If you want a simple demonstration of air density vs. temperature inflate a balloon and then put it in the freezer. I never actually tried it in a freezer but I have seen them change size going inside to out in zubfreezing weather, maybe the temp affects the elasticity of the balloon too so this might not the be the most scientific but it does simply demonstrate the point.
Dynos are generally setup to correct the output numbers for weather conditions, this is why you sometimes see STD or SAE correction factors listed on dyno graphs. So in theory you should be able to dyno a car in Alaska outdoors at sealevel under high pressure in January and get the same treading as a 90 degree day in Dever or a 100 degree day in Vegas or whatever.
Often though tuning is not optimized across all weather conditions though and the output number will change.
There was a time when my car There was a time when my car lost a solid .6-7 from weather alone, what I found was the tuner I had used had halfassed the tune and had not changed some of the temperature vs. spark tables and in the hot weather it read a little knock and pulled a bunch of timing reducing power even more than what the over 100degree temps and high humidity were doing for me..
If you want a simple demonstration of air density vs. temperature inflate a balloon and then put it in the freezer. I never actually tried it in a freezer but I have seen them change size going inside to out in zubfreezing weather, maybe the temp affects the elasticity of the balloon too so this might not the be the most scientific but it does simply demonstrate the point.
10-24-2012, 05:10 PM
#19
Pressure and temperature are directly related, so when you fill a balloon with warm/room temperature air and immediately put it inside the freezer or any cold environment the air pressure inside the balloon drops thus making the balloon shrink.