I'm thinking about running my car in a few weeks. As some of you guys know, the Southeast is extremely humid in the summertime. How much of a difference have you guys noticed in your ET and trap when you race in the winter compared to the summer?

 

The humidity isn't what does it (humidity has very little effect on performance, though it does a small amount). Temperature and atmospheric pressure are what make the biggest difference. From winter to summer, obviously temp is what varies the most. My times (with my old N/A car) varied by about .2-3 seconds and 2-3 mph from 50 degree weather to 80 degree weather, with the pressure being the same. It's a pretty significant difference.

 

Winter? The tracks are open in the winter? Isn't it hard to race in the snow?

Oh you're not in Canada you say...? Nevermind. lol.

Must be nice to be able to race year round.

 

So as far as temperature is concerned the lower the temperature the faster your car will run or is there a threshold of where temperature negatively affects the car's performance? (assuming snow and ice aren't a factor)

Is atmosperic pressure directly related to distance to sea level?

 

The colder the temperature the more dense the air is so the more power you make, however traction on the track will suffer if it gets too cold...

Pressure decreases with increasing altitude yes...

 

Like the other's have said. It's all about dencity altitude.

Dencity Altitude [DA] is pressure altitude [altitude of track adjusted for non standard pressure] corected for non standard temp. Standard Pressure at sea level is 29.92"Hg and roughly 65F.

When you have a barometric pressure of 30.92"Hg @ 65F that is a DA of -1000' below sea level. This means that air is dencer, containing more O2. With every 1000' change your car makes or looses between 2% and 3% power.

In the winter you also see temps below 65F and with lower temps DA falls as well. That is why your car makes more power, and runs faster in the 1/4.

I check the DA before every time I go to the track. That way I know what to expect my car to run. If I am looking for a new best, I will wait for the day with a low temp and a high baromiter, that will give me the lowest DA, most O2, and the car will run faster.

 

agree with neal around .2 difference for me back home, dont get to race in cold weather here which is a bummer.

 

Good info, makes sense.
So would this 2-3% power difference show on a Dyno or is that what SAE correction is for?

 

I saw the same exact thing.