You need to look at density altitude to get corrected elevations based on actual elevation/temp/dew point/baro pressure, then you can relate that to horsepower. This is where aviation and racing agree
Density altitude correction:
http://www.wahiduddin.net/calc/calc_da_em.htm
I did some looking and weather history. Check the date we were at Steele Al to see if it is correct ( I could not find my time slips)
1/10/04 Steele Al. 2pm
Elevation:569 temp:37 DP:25 press:30.37
corrected elevation: 1234 BELOW sea level mmmmmm good
4/17/04 Bowling Green Ky V10 nats 2pm
ele:547 temp:80 DP:64 press:30.25
corrected elevation: 1859 above sea level
Bradenton Fl. V10 nats 2/8/04 2pm
ele:31 temp:59 DP:30 press:30.35
corrected elevation: 378 BELOW sea level mmmmm good
A quick calculation based on those corrected elevations:
If a car had 500hp/rwhp at Steele then there would be a 55hp loss at Bowling Green and 40hp loss at Bradenton.