Drag strip gurus... got a question for ya!
01-18-2001, 06:17 PM
#1
Three Wheelin'
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Drag strip gurus... got a question for ya!
I was just reading a review on edmunds.com and was surprised by how much they estimated their accleration tests were affected by altitude. The test subject was a 2001 Aurora 4.0 and the tests were conducted at an elevation of 3000 feet. Here were the numbers:
0-60: 9.0
1/4 mi: 16.8 @ 84mph.
They said they expected these numbers to be off by at least a full second!! They estimated the 0-60 at 7.6-7.8 seconds at sea level. Would just 3000 feet make that much difference??? I would have thought you had to be up to about 5000 ft to get that much of a difference. I mean... a full second is quite a bit!!! Is there a rule of thumb that says you lose "x" amount of time for every "y" number of feet?
I haven't been to the track with my car yet, but I have a feeling that it's gonna be pretty depressing when I go because Tucson's track is at an elevation of 2800ft! I'll be lucky to break 15s!!!!!!
0-60: 9.0
1/4 mi: 16.8 @ 84mph.
They said they expected these numbers to be off by at least a full second!! They estimated the 0-60 at 7.6-7.8 seconds at sea level. Would just 3000 feet make that much difference??? I would have thought you had to be up to about 5000 ft to get that much of a difference. I mean... a full second is quite a bit!!! Is there a rule of thumb that says you lose "x" amount of time for every "y" number of feet?
I haven't been to the track with my car yet, but I have a feeling that it's gonna be pretty depressing when I go because Tucson's track is at an elevation of 2800ft! I'll be lucky to break 15s!!!!!!
01-18-2001, 06:33 PM
#2
Suzuka Master
Hmmm... Without pulling out all of those nasty equations... Here is an excerpt from an interesting page/link:
Answer: In the same way that you loose HP when you travel at altitude because the air is less dense, you gain it by increasing the pressure. For example, if you travel at 6500 feet, the air is 3PSI less dense than at sea level.(on average) This 3PSI doesn't seem like much, but can be responsible for up to a 20% HP loss. If you could produce a 3 PSI supercharger, your gains could be in this range too. (Ignoring the heating of air due to compression) At 1/2 PSI, gains are in the 3% percent range.
The page is talking about an electric supercharger (losses at altitude, effects of temp, etc). I'll let you judge. (I don't have the exact drop in HP for your altitude).
Here is the link:
http://www.electricsupercharger.com/...com/eramqa.htm
Best I could come up with at this moment...
Answer: In the same way that you loose HP when you travel at altitude because the air is less dense, you gain it by increasing the pressure. For example, if you travel at 6500 feet, the air is 3PSI less dense than at sea level.(on average) This 3PSI doesn't seem like much, but can be responsible for up to a 20% HP loss. If you could produce a 3 PSI supercharger, your gains could be in this range too. (Ignoring the heating of air due to compression) At 1/2 PSI, gains are in the 3% percent range.
The page is talking about an electric supercharger (losses at altitude, effects of temp, etc). I'll let you judge. (I don't have the exact drop in HP for your altitude).
Here is the link:
http://www.electricsupercharger.com/...com/eramqa.htm
Best I could come up with at this moment...
01-18-2001, 07:03 PM
#3
Suzuka Master
Finally, the power created by your engine, assuming that the temp. stays the same is based on change in air density (This means that a weather front will mess up your power a little bit.) Air density is directly related to pressure (if temp stays the same). Look up Boyle's law if you don't believe me...
Feet Pressure Relative
mb Pressure
----------------------------
0 1,013 100.0% Sea level
3,281 899 88.7%
6,562 795 78.5%
9,843 701 69.2%
13,123 616 60.8%
16,404 540 53.3%
19,685 472 46.6%
22,966 411 40.5%
26,247 356 35.1%
29,528 307 30.3%
32,808 264 26.1%
Hp loss = pressure at see level - relative pressure at feet.
So, at 3,281 feet, loss would be 100.0 - 88.7 = 11.3%.
Finally, here is the link to the HP 1/4 mile calculator page so you can figure out your times based on hp...
http://members.aol.com/topfiero/math.htm
[This message has been edited by EricL (edited 01-18-2001).]
Feet Pressure Relative
mb Pressure
----------------------------
0 1,013 100.0% Sea level
3,281 899 88.7%
6,562 795 78.5%
9,843 701 69.2%
13,123 616 60.8%
16,404 540 53.3%
19,685 472 46.6%
22,966 411 40.5%
26,247 356 35.1%
29,528 307 30.3%
32,808 264 26.1%
Hp loss = pressure at see level - relative pressure at feet.
So, at 3,281 feet, loss would be 100.0 - 88.7 = 11.3%.
Finally, here is the link to the HP 1/4 mile calculator page so you can figure out your times based on hp...
http://members.aol.com/topfiero/math.htm
[This message has been edited by EricL (edited 01-18-2001).]
01-18-2001, 08:01 PM
#4
teh Senior Instigator
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in english =
sea level air is thicker w/ more oxygen when compared to air at higher elevations that creates less oxygen
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sea level air is thicker w/ more oxygen when compared to air at higher elevations that creates less oxygen
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01-18-2001, 08:46 PM
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Suzuka Master
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<font face="Verdana, Arial" size="2">Originally posted by EricL:
Finally, the power created by your engine, assuming that the temp. stays the same is based on change in air density (This means that a weather front will mess up your power a little bit.) Air density is directly related to pressure (if temp stays the same). Look up Boyle's law if you don't believe me...
Feet Pressure Relative
mb Pressure </font>
Finally, the power created by your engine, assuming that the temp. stays the same is based on change in air density (This means that a weather front will mess up your power a little bit.) Air density is directly related to pressure (if temp stays the same). Look up Boyle's law if you don't believe me...
Feet Pressure Relative
mb Pressure </font>
------------------
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01-18-2001, 11:58 PM
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<font face="Verdana, Arial" size="2">Originally posted by GoldTypeS:
I haven't been to the track with my car yet, but I have a feeling that it's gonna be pretty depressing when I go because Tucson's track is at an elevation of 2800ft! I'll be lucky to break 15s!!!!!!</font>
I haven't been to the track with my car yet, but I have a feeling that it's gonna be pretty depressing when I go because Tucson's track is at an elevation of 2800ft! I'll be lucky to break 15s!!!!!!</font>
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01-19-2001, 12:16 AM
#8
Suzuka Master
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http://www.prestage.com/carmath/NHRA...on_Factors.asp
As in the above link altitude is more commonly used, but it should be more based on baro. Which is the ultimate value.
As you go up in altitude baro normally decreases. But this is still influenced by weather.
Now humidity does have a definite effect. Moreso than is commonly thought. One problem is that most dyno's don't re-cal their humidity sensors regularly. A drift
of 1%/year is not unheard of.
BTW, I have been to Atlanta Dragway (~1200'), Silver Dollar Raceway and Rockingham and have never been given a time slip with a corrected ET. Not sure what is done up north though, but considering most are < 500' why would they even bother with corrected slips.
As in the above link altitude is more commonly used, but it should be more based on baro. Which is the ultimate value.
As you go up in altitude baro normally decreases. But this is still influenced by weather.
Now humidity does have a definite effect. Moreso than is commonly thought. One problem is that most dyno's don't re-cal their humidity sensors regularly. A drift
of 1%/year is not unheard of.
BTW, I have been to Atlanta Dragway (~1200'), Silver Dollar Raceway and Rockingham and have never been given a time slip with a corrected ET. Not sure what is done up north though, but considering most are < 500' why would they even bother with corrected slips.
01-19-2001, 12:38 AM
#9
teh Senior Instigator
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<font face="Verdana, Arial" size="2">Originally posted by Mike:
Goldy, come to the track with us on 2/3/01!!!!!!!!
</font>
Goldy, come to the track with us on 2/3/01!!!!!!!!
</font>
------------------
pays to be young and crazy
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01-19-2001, 03:15 AM
#11
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::whooooosh::
That just flew right over my head.
Physics, eh? Hopefully I won't have to take that class ever again.
------------------
~Phil~!
2K1 CL-S since 6/13/00 named Laetitia! Quantum tint, hyper-white road lamps, and I just got a spoiler on baby!! Uniden LRD 6599SWS Radar Detector. Beautiful shine provided by Meguiar's Gold Wax. Shuttup, I know it's not Zaino
Former post count : Over 470
That just flew right over my head.
Physics, eh? Hopefully I won't have to take that class ever again.
------------------
~Phil~!
2K1 CL-S since 6/13/00 named Laetitia! Quantum tint, hyper-white road lamps, and I just got a spoiler on baby!! Uniden LRD 6599SWS Radar Detector. Beautiful shine provided by Meguiar's Gold Wax. Shuttup, I know it's not Zaino
Former post count : Over 470
01-19-2001, 10:15 AM
#12
Three Wheelin'
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<font face="Verdana, Arial" size="2">Originally posted by scalbert:
http://www.prestage.com/carmath/NHRA...on_Factors.asp
As in the above link altitude is more commonly used, but it should be more based on baro. Which is the ultimate value.
As you go up in altitude baro normally decreases. But this is still influenced by weather.
Now humidity does have a definite effect. Moreso than is commonly thought. One problem is that most dyno's don't re-cal their humidity sensors regularly. A drift
of 1%/year is not unheard of.
BTW, I have been to Atlanta Dragway (~1200'), Silver Dollar Raceway and Rockingham and have never been given a time slip with a corrected ET. Not sure what is done up north though, but considering most are < 500' why would they even bother with corrected slips.</font>
http://www.prestage.com/carmath/NHRA...on_Factors.asp
As in the above link altitude is more commonly used, but it should be more based on baro. Which is the ultimate value.
As you go up in altitude baro normally decreases. But this is still influenced by weather.
Now humidity does have a definite effect. Moreso than is commonly thought. One problem is that most dyno's don't re-cal their humidity sensors regularly. A drift
of 1%/year is not unheard of.
BTW, I have been to Atlanta Dragway (~1200'), Silver Dollar Raceway and Rockingham and have never been given a time slip with a corrected ET. Not sure what is done up north though, but considering most are < 500' why would they even bother with corrected slips.</font>
I plugged in the numbers:
At sea level this car should get:
0-60: 8.67
1/4 mi: 16.2 @ 87.2mph
Edmunds sucks!! Yeah, I guess I already kinda new that!!! Their estimations that they'd gain "at least a full second" may not be correct if these calculations are accurate. I knew that didn't sound right!! OTOH... we're they even flooring this car when they tested it??? I know the Aurora V8 is kinda heavy, but these are Civic EX numbers. That's PATHETIC!! Yeah, I'll say it again.... Edmunds sucks for performance number!
01-19-2001, 12:51 PM
#13
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pphhhhaaattt!!! you don't need an invitation. get down here!
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<font face="Verdana, Arial" size="2">Originally posted by CLpower:
thanx for inviting me pops! carlsbad is fast
</font>
thanx for inviting me pops! carlsbad is fast
</font>
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01-19-2001, 01:19 PM
#14
Three Wheelin'
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<font face="Verdana, Arial" size="2">Originally posted by Mike:
Goldy, come to the track with us on 2/3/01!!!!!!!!
</font>
Goldy, come to the track with us on 2/3/01!!!!!!!!
</font>
01-19-2001, 01:21 PM
#15
Advanced
You could use the calculator/formulae approach or you could hop in your dramatically pedestrian '77 VW Bus and get a real feel for the impact of various altitudes. Home is 1400'. Drive to the coast, 5' +/-, all 68 horses waken and 0-60 in less time than it takes to spell check this mess. Conversly, drive up into the mountains 6000' +/-, and 60 mph is only possible on the down hill. Bigger motors just mask the "altitude effect".
01-19-2001, 07:47 PM
#16
Suzuka Master
BTW -- all of the formulas etc don't apply to Turbocharged cars with wastegates (constant pressure). They will adjust for altitude.
That's why they turbo-supercharge piston airplanes. Good performance at altitude...
That's why they turbo-supercharge piston airplanes. Good performance at altitude...
01-20-2001, 02:25 PM
#17
Suzuka Master
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Actually most turbo cars don't adjust to altitude. However, they don't suffer as bad as NA engines.
But the last gen RX-7, sequential turbo rotary, did adjust boost according to start up barometric pressure. So that when altitude did increase and the subsequent drop in baro, the boost was raised.
But the last gen RX-7, sequential turbo rotary, did adjust boost according to start up barometric pressure. So that when altitude did increase and the subsequent drop in baro, the boost was raised.
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