How much of a difference does DA make on your ET? The DA is consistently over 1000' over here. Sometimes, it can get as bad as 2000'. I see some of you all have negative DAs in your towns, especially in the colder areas and make some awesome passes for such mild combos. (Vic'89 for example) Is there a formula or any other type of way to calculate how good of a pass you can make in relation to the current DA?

 

This should help:

http://www.hardtail.com/techtips/altitude.html

I've seen some that you can input and I assume you can input a negative elevation as well with those, but I cannot find one online at the moment.

 

Damn, so if I ran what I run usually run, but in a 0 DA, I could probably be running close to the high 10s and trapping up to 126 mph. Now that is AWESOME!!!

 

Yeah, a lot of people forget or just don't know how much of a difference it makes. Lots of 'factory freaks' can be attributed to good driving and great weather.

 

Send me a truck load of that air. Our DA rarely drops to 6000' and usually is over 7000'. The NHRA chart provided is for the purposes of altitude correction, ONLY, not density altitude. No one officially corrects for weather conditions. The author of that link interchanges the two terms without explaining the distinction. He starts out saying that NHRA has correction factors for altitude. Then he says, "If you really want an accurate conversion, then do your calculations with density altitude", and finally ends up with the NHRA factors. He treats altitude and DA interchangeably as the same thing. They are not.


NHRA doesn't apply a correction factor to any location under 1200' (or is it 1600'). What is the highest altitude in Florida, 30'? Your local tracks have a correction factor of, nothing. If you were to contend that the 11.364 ET in your sig came in 2000 DA, and you incorrectly applied the correction factor for 2000' altitude to that ET, it only factors to a [11.364 X .9770 =] 11.103.

RACE ON!!!

 

A decent rule of thumb is .01sec for every 100ft DA change. Most of us that race all the time you will see us posting the DA in our threads when stating ET/MPH gains. This puts into perspective our times vs those that enjoy better weather.

We rarely if ever see anything less than 1200 ft DA, since that is about the elevation physically of the track above sea level.

Beware though its not always the case and why a good racer will KNOW their own car and be able to tell that weather will do to it. It take a long time to get good at it and just when you think you have it figured out, you will make a pass and loose and not be able to figure out the slip - that is why bracket racing is MUCH more than just putting a time on your window and driving in a straight line. You will learn more about your car, your tuning, and suspension than you ever imagined - if you care to get deeply involved in it.

I have found that humidity will cause my car to change more than the actual number shown on the TAG (hand weather device that calculates DA off temp, humidity, and BP). If I see a big gain in humidity, the car will slow more than normal. This seems to happen at night when you get that dew on your car in the pits....I will slow down about .075sec (usually, until a tailwind comes along and you break out.


Best thing you can do is start a log and keep track of your runs and weather, you will start to see some patterns.

 

A DA of 1000' - 2000' is not that bad, In the summer I will run in 2500+ DA. I run about 11.6's in this weather.

In the spring and fall, we do get a negative DA and the car will run faster.

For me, it calculates to 1 tenth for every 1000'.

Vic