I sure see some awesome "Altitude Corrected" E/Ts floating around these days. I can buy into an altitude corrected power rating as long as its normally aspirated, but I have a few questions concerning the posting (or boasting) of an altitude corrected E/T.

Let's assume one has a 115 MPH trap speed at Bandimere Speedway in Denver. The proud timeslip holder can then brag about their "120 MPH" altitude corrected trap speed? What about the large increase in airflow across the car at a true 120MPH? What about the increase in detonation resistance of the mountain air, and subsequent advance in timing?

Could someone enlighten me as to the legitimacy, and proper use of "altitude corrected" statistics?


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Daniel Burk
http://www.isthq.com/~dan/fcar.html
'84 Trans Am WS6/L69
KB SFC, Moser axles, Torsen Diff. PST suspension, Braided stainless brake lines, Koni struts, 11-inch rear disks,Spohn Adj. torque arm,
Ported 305 heads w/1.94"intake valves, Comp Cams XE262H, Griffen alum. radiator,
Turbine Technologies 2500 stall converter, underdrive pulleys, Crane Hi-6 & more.
1.05g skidpad verified.
New best E/T! 14.039 at 100.82 MPH at Stanton, Michigan Elevation: 712 feet.

"Altitude corrected" to 13.79 at 101.8 MPH.



[This message has been edited by ws6transam (edited January 30, 2001).]

 

The tables are used simply as a comparison -- apples to apples. Whenever I post times, they are always altitude corrected for 3100 feet (my track is at 3070 feet officially). Otherwise, it wouldn't be fair to anyone. When I talk locally, I talk in actual time.

I can't answer your specific questions, but I would tend to think that NHRA did factor in all the points you mention when creating their altitude correction tables. If you want a copy, e-mail me.

------------------
Willie

Supercharged 1987 305 IROC-Z, Daily-Driver, Emissions-Legal.
12.57 @ 111 mph.
12.04 @ 114 mph (50-hp nitrous).
http://members.optushome.com/au/downunder1/rides/willie/willie.html

1987 "20th Anniversary Commemorative Edition" Z28 Convertible -- Super Chevy Show Class Winner, 1998.

 

I would indeed find it an interesting read. Is your table set electronic or on paper?

 

You might click on:

gafba.com/calculators/et1.asp

which is the Georgia F-bodys download of NHRA corrections.

It corrects altitude, temperature, and barometric pressure to standards.

My best run was on a 90* day and turned a 13.10 into a 12.84.

Throw in altitude and pressure and it became 12.68 ET.

Apples and apples.....it's the only fair way, otherwise guys up in Denver would have a huge automatic penalty because it's the "mile-high" city. Also, us Southern boys look slow running in this heat. Now you know why I always loved those cool Wisconsin nights at Great Lakes Dragway - better timeslips !


BOR

 

I agree with Wille that it is totally unfair to compare a car that runs at 3,100' vs a car that runs at sea level WITHOUT using correction tables. The thinner air of the 3,100' track makes it impossible for the car to perform as it could if it was at sea level.

Now, if you are asking "If I take that car that ran a corrected ET of xx.xx, will it get the xx.xx at a track at sea level"? The answer is "Maybe".

If car that run the corrected time of xx.xx at 3,100' was optimized for 3,100', it would need to be re-optimized for sea level. Conversely, the same thing for a car optimized to run at sea level, would need to be optimized to run at 3,100' for it to hope to run a corrected time the equivalent he did at sea level. EFI makes this a lot easier, but with a carb this is a major concern.

 

I couldn't agree with Glenn any more. When my PROM was burned, TPIS did ask me what altitude I run at. Maybe some of you PROM burning gurus (Glenn, are you with me?) can explain what parameters are changed on a PROM designed for altitude.

My NHRA Correction Tables are hardcopy that I've scanned. Again, if anyone wants them, e-mail me.

Willie

 

Less wot fuel and more wot timing... engine will also idle at a different manifold pressure... if at sea level it idles at 15", up here in 6000' colorado springs, it will idle at around 11". The motor is going to want more timing everywhere due to less efficant combustion with the thinner air charge... makes a 10:1 cr motor run soggy like an 8:1 motor.

 

The Calgary Drag Racing site has the correction chart. NHRA somehow came up with the formula to calculate altitude correction but when they use it, they only calculate elevation and not density altitude. Calgary is 3500 feet elevation but during the summer the density altitude is usually always over 5000 feet.

When there's an NHRA event in Boise Id, NHRA records are uaually broken because of the altitude correction. Early morning runs can make the density altitude lower than the actual elevation but the ET is calculated from the elevation so a quick pass can become an altitude corrected record.

When looking through stock eliminator records you'll notice most of them are set at altitude tracks. All the correction factor means is that theoretically that car should run that ET at sea level on a perfect day of 60 degree F, 0% humidity and 29.92 barometer.

------------------
Follow my racing progress on Stephen's racing page
and check out the race car

87 IROC-Z Pro ET Bracket Race Car
383 stroker (carbed) with double hump cast iron heads and pump gas
461 Big Block installed and ready for the 2001 racing season

Best results before the 383 blew up
Best ET on a time slip: 11.857 altitude corrected to 11.163
Best MPH on a time slip: 117.87 altitude corrected to 126.10
Altitude corrected rear wheel HP based on power to weight ratio: 476.5
Best 60 foot: 1.662

Racing at 3500 feet elevation but most race days it's over 5000 feet density altitude!
Member of the Calgary Drag Racing Association

87 IROC bracket car, 91 454SS daily driver, 95 Homebuilt Harley

 

"Density" altitude seems to be a function of air temperature rather than true altitude. Is this right?

thanks for the link, BOR. It was enlightening!

 

Density altitude is a combination of elevation, temperature, humidity and barometric pressure. It's used more by pilots than it is by racers.