Bristol June 10th pics, post them here.
BOOST!
Joined: Dec 2002
Posts: 951
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From: Blacksburg, VA
Originally posted by Grendelrt(va)
Nick you ran a 13.5 @ only 4 lbs of boost? Man thats damn impressive! What was your time before correction?
Nick you ran a 13.5 @ only 4 lbs of boost? Man thats damn impressive! What was your time before correction?
13.75@108.63 is the actual
Nick
KA powered S14
Joined: Jan 2003
Posts: 421
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From: blacksburg, va
damn, nick, now that i think about it, you should've filled up with some 101 octane like ben did last time, hehe. maybe it would've given a better time than your already really good time, hehe.
Registered Member
Joined: Nov 2002
Posts: 378
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Originally posted by V8BRICK
I'm gonna argue these correction factors. True NRHA is the authority, but those numbers aren't on turbo-charged cars.
Here's and excerpt from a site that makes sense of determining the handicap of altitude and turbo engines. Doesn't take into account the lag time when you have no boost, but it's closer than the NHRA's fantasy corrections:
"CORRECTING FOR ALTITUDE
If we were dealing with non-turbo cars, this would be easy and we'd publish a formula. But with pressurized cars, the correction factor for altitude depends on the boost you run.
For instance, Sea Level air pressure is 14.7 psi. If you go to a track in Boise, Idaho (2850 feet above sea level) the air pressure is now around 13.25 psi. That's 90.1% of sea level pressure. If the temperature doesn't change and you have an normally aspirated car, your power output will now be 90.1% of what it used to be, so I'd tell you to correct by multiplying your calculated HP by an extra 10.9% (1/.901, or 1.109).
However, (and this is the beauty of turbo cars!!) Let's say you were running 10 psi of boost in the first place. So at sea level, your car was really getting 24.7 psi (14.7 + 10). Now you leave the wastegate at 10 psi and race at Boise. Your manifold pressure is now 23.25 psi (13.25 + 10). Note that YOUR power isn't down as much.. it's down to 94.1% of what it is at sea level. So you should correct with an extra 6.2% (1/.941, or 1.062).
If you wish to calculate your own correction factor, here is a handy table of elevation (feet above sea level) vs. standard day atmospheric pressure (psi):
http://www-unix.oit.umass.edu/~tcroy...dollardyno.htm
0 14.70
500 14.43
1000 14.18
1500 13.92
2000 13.67
2500 13.42
3000 13.17
3500 12.92
4000 12.69
4500 12.45
5000 12.23
5500 12.00
6000 11.78
6500 11.56
7000 11.34
7500 11.13
8000 10.91
8500 10.71
9000 10.51
9500 10.30
10000 10.11 "
So depending on boost levels, this is the way I'd calculate my corrections.
I'm gonna argue these correction factors. True NRHA is the authority, but those numbers aren't on turbo-charged cars.
Here's and excerpt from a site that makes sense of determining the handicap of altitude and turbo engines. Doesn't take into account the lag time when you have no boost, but it's closer than the NHRA's fantasy corrections:
"CORRECTING FOR ALTITUDE
If we were dealing with non-turbo cars, this would be easy and we'd publish a formula. But with pressurized cars, the correction factor for altitude depends on the boost you run.
For instance, Sea Level air pressure is 14.7 psi. If you go to a track in Boise, Idaho (2850 feet above sea level) the air pressure is now around 13.25 psi. That's 90.1% of sea level pressure. If the temperature doesn't change and you have an normally aspirated car, your power output will now be 90.1% of what it used to be, so I'd tell you to correct by multiplying your calculated HP by an extra 10.9% (1/.901, or 1.109).
However, (and this is the beauty of turbo cars!!) Let's say you were running 10 psi of boost in the first place. So at sea level, your car was really getting 24.7 psi (14.7 + 10). Now you leave the wastegate at 10 psi and race at Boise. Your manifold pressure is now 23.25 psi (13.25 + 10). Note that YOUR power isn't down as much.. it's down to 94.1% of what it is at sea level. So you should correct with an extra 6.2% (1/.941, or 1.062).
If you wish to calculate your own correction factor, here is a handy table of elevation (feet above sea level) vs. standard day atmospheric pressure (psi):
http://www-unix.oit.umass.edu/~tcroy...dollardyno.htm
0 14.70
500 14.43
1000 14.18
1500 13.92
2000 13.67
2500 13.42
3000 13.17
3500 12.92
4000 12.69
4500 12.45
5000 12.23
5500 12.00
6000 11.78
6500 11.56
7000 11.34
7500 11.13
8000 10.91
8500 10.71
9000 10.51
9500 10.30
10000 10.11 "
So depending on boost levels, this is the way I'd calculate my corrections.
Anyone?
VIP Boost
Joined: Jan 2003
Posts: 149
Likes: 0
From: SOVA
The pressure ratios for the turbo charged car are diffrent for the 2 diffrent elevations. So you could be loosing power just because you are going into a diffrent area of your flow map.
Pressure Ratio (ATM+Boost)/ATM
(14.7+10)/14.7 = 1.680
(13.25+10)/13.25 = 1.755
Higher pressure ratios will move your point higher up on the compresser map. Most of us will suffer from lower efficency, unless we are running very large turbos. We will probably even hit the surge line upto a higher RPM then we would at lower elevation.
Not only that, but your VE (volumetric efficency) is also lowered at the higher altitude, even on a turbo car. You dont have 100% efficency in getting all of the compressed air into the cylinders. The cylinders are starting out at a lower pressure then they would at lower altitude.
So I think what Elijah said, although somewhat true, does not take into consideration all of the factors that go into determining power loss. Also the correction during the time that you are off boost or when boost is coming up or falling.
The system is so dynamic, that you cant just use one boost number to find the correct answer.
Eric
Pressure Ratio (ATM+Boost)/ATM
(14.7+10)/14.7 = 1.680
(13.25+10)/13.25 = 1.755
Higher pressure ratios will move your point higher up on the compresser map. Most of us will suffer from lower efficency, unless we are running very large turbos. We will probably even hit the surge line upto a higher RPM then we would at lower elevation.
Not only that, but your VE (volumetric efficency) is also lowered at the higher altitude, even on a turbo car. You dont have 100% efficency in getting all of the compressed air into the cylinders. The cylinders are starting out at a lower pressure then they would at lower altitude.
So I think what Elijah said, although somewhat true, does not take into consideration all of the factors that go into determining power loss. Also the correction during the time that you are off boost or when boost is coming up or falling.
The system is so dynamic, that you cant just use one boost number to find the correct answer.
Eric
Registered Member
Joined: Nov 2002
Posts: 378
Likes: 0
Originally posted by rhombus
The pressure ratios for the turbo charged car are diffrent for the 2 diffrent elevations. So you could be loosing power just because you are going into a diffrent area of your flow map.
Pressure Ratio (ATM+Boost)/ATM
(14.7+10)/14.7 = 1.680
(13.25+10)/13.25 = 1.755
Higher pressure ratios will move your point higher up on the compresser map. Most of us will suffer from lower efficency, unless we are running very large turbos. We will probably even hit the surge line upto a higher RPM then we would at lower elevation.
The pressure ratios for the turbo charged car are diffrent for the 2 diffrent elevations. So you could be loosing power just because you are going into a diffrent area of your flow map.
Pressure Ratio (ATM+Boost)/ATM
(14.7+10)/14.7 = 1.680
(13.25+10)/13.25 = 1.755
Higher pressure ratios will move your point higher up on the compresser map. Most of us will suffer from lower efficency, unless we are running very large turbos. We will probably even hit the surge line upto a higher RPM then we would at lower elevation.
Not only that, but your VE (volumetric efficency) is also lowered at the higher altitude, even on a turbo car. You dont have 100% efficency in getting all of the compressed air into the cylinders. The cylinders are starting out at a lower pressure then they would at lower altitude.
Also - Boost (and efficiency) will vary at different altitudes dependent upon your boost controller. With a manual boost controller, your boost pressure is relative to the ATM pressure. However with an electronic boost controller, if you didn't change the boost setting between different altitudes, you would be boosting higher pressures (relative to ATM) at higher altitudes than lower ones.
Why? The electronic boost controller relies on an electronic pressure sensor to determine the boost pressure. Let's say you set the boost controller to 10psi, and a measurement of 10psi is 3.0 Volts on the electronic sensor... Well the electronic boost controller is totally ignorant to the current atmospheric pressure (because it assumes that the ATM is 14.7), and will strive to sustain a boost level of 10psi + 14.7psi absulute pressure.
Anyway...So if the atmospheric pressure drops 1.45psi (as in eric's example), then the boost (relative to the ATM of 13.25) will be 10psi + 1.45psi.
Ya'll bitches followin me?
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