Just curious if one of the 3 actually limits cars more so than the other two. Obviously all three play their role, but is there one which scientifically is more harsh on our cars?

I ask this because of a recent race we did. Since I've been in Lubbock for school all I hear about day in and day out is that cars that race in Lubbock will actually be significantly faster in San Antonio (Seguin). They claim this is due to elevation ~600' vs. ~2800-3200' (not sure on Idalou raceway). Most people claimed that it would be a difference of approximately .3-.5 in the 1/4 and possibly a gain of a few mph at San Antonio as well. Some (idiots), even claim that .7-.8 will be picked up.

Now I listened to this garbage but noticed the whole time that people with similar mods here were running within .1 either way of time in SA that my friends were running. So here's what we're using to compare (only car we know times for both places)...

NOT a Corvette, or even close, BUT it's n/a.... '00 V-6 Firebird (my roommates) he has headers, cat, no exhaust from there back, Hypertech, intake, better clutch, new tires/wheels, few other insignificant things. Anyway, San Antonio he pulled a BEST of 15.9 @ ~87mph......... he then races in Idalou via everyone's encouragement, and he pulled consistent 15.6 @ 90mph.... that's .3 and 2mph faster at an elevation that is more than 4 times as high. So I ask you, is it merely the humidity factor that central texas and east texas have, or was it sure luck? Temperature was relatively the same, and this was in the same week.

Sorry for the long post, but thanks for any replies ahead of time


[Modified by BowTieBlood, 11:12 PM 7/6/2004]

 

Let me also add.... the day he raced and hit the 15.9 in SA, I pulled consistent 14.35 @ 96mph About 2 months later (same conditions in SA) I pulled consistent 14.2 @ 98mph. The second time was with 60' times of 2.2X, but I don't recall the previous time.

Also, my friend in Idalou only pulled 2.4-2.6 60' times in the Firebird.... in SA he was much faster off the line.

 

I'd like to know this myself. I do know that a high barometer is better for performance as this is like being at a lower elevation.

Wait for the barometer to be high with cool temperatures and you should make more power. I don't know what extra humidity would do. I've heard water injection helps with knock, so maybe higher humidity would help keep knock away ever so slightly??

Running at a higher elevation and if their was a hypothetical hurricane nearby I'd say would not be good for power!


[Modified by LT4fun, 5:48 AM 7/7/2004]

 

http://www.stangbangerz.com/modules....h&file=density

hopefully that link works, that should answer your question

65Z01 also has some formulas in his signature


[Modified by vader86, 12:04 AM 7/7/2004]

 

What you want to know is what affects Density Altitude the most (DA)
I've raced at low altitude and high altitude and it seems that altitude is by far the biggest factor followed by heat and then humidity. Pressure also makes a big difference, which is dramatically affected by altitude and heat.

The lower the DA, the more power you'll make and likewise the faster you'll run. Check this site out and play with the numbers. Set the altitude for 200' and play with the pressure (29.92 is sea level, 27 sucks and 30 is great) as well as the heat. Notice that as heat rises so does the DA. However, humidity seems to have less affect than heat and altitude.

http://wahiduddin.net/calc/calc_da_rh.htm

BTW, the worst place I ever raced was in Vegas,. The elevation was 2200', temp was 98, pressure was ~28.90" and RH was 25% (actually quite humid). I was making about 80% horsepower as compared to sea level, oof!


[Modified by MyX10sion, 1:17 AM 7/7/2004]

 

Cool site.

I need to get some damn weather tools


[Modified by BowTieBlood, 12:14 AM 7/7/2004]

 

Neat links! Thanks!


[Modified by LT4fun, 6:18 AM 7/7/2004]

 

For each 1000 feet in elevation increase you lose 3%of your horsepower. At 6.000 feet you are basically running on 7 cylinders or a 18% loss of power which is 54 hp for an LT1.

 

So if I dyno in Lubbock (3200') and I dyno in Austin, without any corrections for weather or SAE or whatever it is......... it would be around 9% less horse power?

 

Lubbock is 3200? Houston is only 50 feet above sea level. That is one reason the top fuel dragster reach some of there fastest speeds here in Houston(Baytown actually). I know those Pikes Peak race cars loose a large percentage of their power between the beginning of the course and at the top near the end.

 

Yea, Lubbock's on the "caprock." I was shocked by that too, I think Austin's only at like 400-500', or so I thought? Doesn't seem like you're driving up hill, maybe that's why going Lubbock to Austin, I get 1-2 more mpg than the other way.

 

Humidity plays a very large roll. Here in Bowling Green we have near 100% humidity all the time. You can feel that it takes an extra effort to simply walk through the air, let alone push a car along at 100 MPH.

On the off chance that we actually have a low humidity day, such as 70%, everybody runs about 2 tenths better.

 

I bought a weather station and computer in 1994 and it was the best bracket racing/tuning aid I've purchased.

I am not certain how the calculation looks and how it factors each variable, but I observed that static altitude seems to have a greater impact than the weather variables - within reason, meaning you are not comparing a 45 degree day with 20% humidity to a 90 degree day with 70% humidity.

The computer actually get pretty good at predicting ETs once you get a good base line.

 

There was a "hunidity" question asked a while back on the Drag Race forum. Here is a reply I wrote to explain some of the efects of weather and altitude.


Re: Help with humidity... (ROJO99) 5:09 PM 7/1/2004


Humidity takes up space in a cubic foot of atmosphere, leaving less room for the air, which contains approximently 19% oxygen. It IS the oxygen that we're after. The more humidity in the air, the less oxygen available in every cubic foot. The fooler in the humidity reports is, that it is generally reported as "relative humdity".
Warmer air can hold more humidity than cooler air. Relative humidity is the amount of moisture in the air, "relative" to the capacity of the air, to hold moisture, at the reported temperature. I don't have the exact figures, but 80* air with 60% "relative humidity" may contain the same amount of moisture as 100* air at 50% "relative humidity". When the temp drops and the percent of humidity raises, don't assume the presents of more moisture in the air. Therefore the dew point and/or the vapor pressure are better indicaters of the actual amount of moisture present.

Barometric pressure is the number one factor in preformance, as stated. But don't be fooled by the radio or TV, especially if you race tracks at different altitudes. All common weather service barometer readings are "corrected to sea level" readings. Denver and Death Valley may report the same barometer under certain conditions, but their air pressures will never be the same. *I* don't recall seeing an actual barometer over 26" at my home track. Last week, it ranged between 25.72" and 25.75" Denver would be still less.

Just a few "weather facts" for anyone that may care.

RACE ON!!!

 

[BTW, the worst place I ever raced was in Vegas,. The elevation was 2200', temp was 98, pressure was ~28.90" and RH was 25% (actually quite humid). I was making about 80% horsepower as compared to sea level, oof!]


You ought to try racing up here at our track. Our DA is usually between 6000-8500+ ft. Every now and then we see the DA at 5500 ft. We think of Vegas as GOOD air.


[Modified by tpi 421 vette, 12:13 PM 7/7/2004]

 

That site isn't very accurate... It says my 13.37 turned into a 9.34...
Info from my last time slip
Temp = 72
Humidity = 20%
Altitude = 5800 Ft
Pressure = 23.78
ET = 13.37
Trap = 103.9

 

When WE get to Vegas, we think we're in heaven!

RACE ON!!!

 

My friend just told me the DA in Idalou on the night of his 15.6 was at 5700 around 2a.m., close as he knew about to the time he ran. His buddy told him it ranges between 6300-5800 during the times they race, something like that, but could be wrong.

Thanks for all the replies

 

Ok, I found a site that allowed me to convert my Pressure reading to Sea Level and it came up with:

Density Altitude = 8127 feet ET MPH
Uncorrected 13.37 @ 103.9
Corrected 11.75 @ 116.46

 

DA makes a big difference. Why do you think the NJ guys always run so good???