Formula?
 

Can anybody tell me the formula to correct ET's to sea level?

To convert your timeslip ET and MPH to sea level. Multiply applicable factor times your ET or MPH.

(Example: You ran a 14.4 @ 103 MPH at 5000' elevation track. The correction factors are .9367 and 1.0661 for 5000'. (14.4 * .9367) = 13.50 , (103 * 1.0661) = 109.80 MPH. So the correct timeslip would be 13.50 @ 109.80 MPH at sea level)

FT above Sea Level | Elapsed Time | Trap Speed (MPH)

1200 .9874 1.0129
1300 .9861 1.0143
1400 .9848 1.0157
1500 .9835 1.0171
1600 .9822 1.0185
1700 .9809 1.0199
1800 .9796 1.0213
1900 .9783 1.0227
2000 .9770 1.0241
2100 .9757 1.0255
2200 .9744 1.0269
2300 .9731 1.0283
2400 .9718 1.0297
2500 .9705 1.0311
2600 .9692 1.0325
2700 .9679 1.0339
2800 .9666 1.0353
2900 .9653 1.0367
3000 .9640 1.0381
3100 .9627 1.0395
3200 .9614 1.0409
3300 .9601 1.0423
3400 .9588 1.0437
3500 .9575 1.0451
3600 .9562 1.0465
3700 .9549 1.0479
3800 .9536 1.0493
3900 .9523 1.0507
4000 .9510 1.0521
4100 .9497 1.0535
4200 .9484 1.0549
4300 .9471 1.0563
4400 .9458 1.0577
4500 .9445 1.0591
4600 .9432 1.0605
4700 .9419 1.0619
4800 .9406 1.0633
4900 .9393 1.0647
5000 .9380 1.0661
5100 .9367 1.0675
5200 .9354 1.0689
5300 .9341 1.0703
5400 .9328 1.0717
5500 .9315 1.0731

The differences are .0013 per 100ft on the time and .0026 per 100ft on the mph.

Was the 2000' the physical altitude or the density altitude? More times than not, the density altitude far outweighs the correction required for the physical altitude. For example, Norwalk (my home track) is only at 742' physical altitude but during the summer months its pretty common for the density altitude on any given day to be in excess of 2500'. This is because of the combined effects of barometric pressure, humidity and temperature. The last two times I've been out for TnT, the barometric pressure has been in the mud at less than 28.9 in-Hg. That's a killer for an N/A car....the density altitiude was at more than 3800' both times. That's why you'll see the serious racers with a weather station; to help them really tune to the conditions. Being a carbureted car, I can usually tune more than two-tenths of a second based on weather alone. That's huge when you're racing heads-up.

the Physical altitude was 2100 ft. I have no idea what the density altitude was. Next time I'll have to ask the guys with the weather stations. Thanks guys!