Temp affect on E.T.

[terry5357]

Does anyone know how much every 10 degree increase in temp decrease run times. In March I can turn8.60's or better and in the summer I am lucky to pull an 8.78

 

[don_w]

I don't think there is a good rule of thumb for that... too many other variables in play as well (such as humidity, track temp, etc.). Also, an extremely cold night can be worse than one a little warmer.

 

[fin1]

Like Don said, it more than just air temp. If the temperature increases but say the relative humidity drops, your car could run the same or possibly faster. The best indicator is density altitude (DA). Since it factors in pressure, humidity and temperature, it makes it easy to see how weather affects your ET as you compare runs over time.

 

[don_w]

The best indicator is density altitude (DA). Since it factors in pressure, humidity and temperature, it makes it easy to see how weather affects your ET as you compare runs over time.

While I agree that DA is probably the best indicator, I have noticed that it is less reliable for a blown car than for one that is NA. For example, many times my car will run considerably different ETs, even though the DA is the same. I suspect that the blower is compensating for fluctuations in barometric pressure, rendering it less of a factor. The ETs vary slightly with temp, but the biggest factor I see with my car is humidity. No matter what you do, excess water in the air hurts. Funny thing about water... you can't compress it and you can't burn it. I've run better ETs during the dry daylight hours, than I have later on in the evening when it cooled off and the humidity went up.

 

[fin1]

the biggest factor I see with my car is humidity.

It's the same with mine car too Don. I wasn't trying to say DA was the beat-all-end-all of ET prediction but it's more reliable than just air temp.

 

[don_w]

I wasn't disagreeing Brad... just adding my based on what I've noticed.

 

[gmantheman]

I might go up to Barona today and see how I do. Last time there my fastest time was 9.352... but the DA was around 4300' so if my calculations are correct, that would be abou 8.835 at sea level.