Dyno Runs / Correction Factors
10-29-2009, 05:46 PM
#46
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Again, no. Manifold pressure is the pressure differential, it is not absolute pressure.
Pretty much all gauges read manifold pressure (the pressure differential), not absolute pressure. Can my turbo make the same absolute pressure as someone at sea-level, yes. However, it forces the turbo to work harder (about 3psi harder), lowering VE. Subsequently lowers HP/TQ.
If you don't believe me, I invite anyone to set their boost at sea-level, then come up to Denver and see for themselves.
Airplanes that use turbo normalizing to make up for the pressure loss at high altitudes, run a quit a bit of boost pressure just to get back to "0" (or sea-level). An airplane at 20,000ft requires nearly 8psi of positive manifold pressure to have the same absolute pressure as it would at sea-level w/ 0psi of boost.
-Rogue
Pretty much all gauges read manifold pressure (the pressure differential), not absolute pressure. Can my turbo make the same absolute pressure as someone at sea-level, yes. However, it forces the turbo to work harder (about 3psi harder), lowering VE. Subsequently lowers HP/TQ.
If you don't believe me, I invite anyone to set their boost at sea-level, then come up to Denver and see for themselves.
Airplanes that use turbo normalizing to make up for the pressure loss at high altitudes, run a quit a bit of boost pressure just to get back to "0" (or sea-level). An airplane at 20,000ft requires nearly 8psi of positive manifold pressure to have the same absolute pressure as it would at sea-level w/ 0psi of boost.
-Rogue
funny, after reading that, we're both saying the same thing, but going about it 2 different ways. I think the way you describe pressure differential and I describe it are two different ways.. But we're coming to the same conclusion. Honestly though.. I ... lol, of course, feel like I'm saying it correctly.. No big deal though if we're coming to the same conclusion. -- Except.. I can't let this go... We ARE saying the same thing if you agree. If my digital gauge with its own map sensor tells me its reading 18psi off the manifold here (Houston) or there (Colorado) .. Its 18psi. I would use that gauge to calculate the pressure differential (knowing the pressure of whatever atmospheric pressure Im at)
I would LOVE to dyno here at 18psi.. keep all else same, and go to Denver and dyno at.... 18psi..
I think I see a bit of humor here. you're saying, ill see less psi if I set my controller here and dont change it, and I will see less psi up there.. HA! YES of course I will.. Im saying that. Im saying, if you run 18psi up there, (No matter how you have to set the controller from different towns) 18psi up there will be almost the same as 18psi down here. Agreably a little down on power in Colorado
Just to stay clear in a very friendly way.. I never described the gauge pressure as absolute. To clear this a little further, Im describing it as the end result pressure after the turbo. Whatever the differential from the outside air, doesn't matter.. If the gauge reads 18psi.. .. There is a total of 18psi of air in there!
Last edited by 95ONE; 10-29-2009 at 06:01 PM.
10-29-2009, 06:20 PM
#47
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funny, after reading that, we're both saying the same thing, but going about it 2 different ways. I think the way you describe pressure differential and I describe it are two different ways.. But we're coming to the same conclusion. Honestly though.. I ... lol, of course, feel like I'm saying it correctly.. No big deal though if we're coming to the same conclusion. -- Except.. I can't let this go... We ARE saying the same thing if you agree. If my digital gauge with its own map sensor tells me its reading 18psi off the manifold here (Houston) or there (Colorado) .. Its 18psi. I would use that gauge to calculate the pressure differential (knowing the pressure of whatever atmospheric pressure Im at)
I would LOVE to dyno here at 18psi.. keep all else same, and go to Denver and dyno at.... 18psi..
I think I see a bit of humor here. you're saying, ill see less psi if I set my controller here and dont change it, and I will see less psi up there.. HA! YES of course I will.. Im saying that. Im saying, if you run 18psi up there, (No matter how you have to set the controller from different towns) 18psi up there will be almost the same as 18psi down here. Agreably a little down on power in Colorado
Just to stay clear in a very friendly way.. I never described the gauge pressure as absolute. To clear this a little further, Im describing it as the end result pressure after the turbo. Whatever the differential from the outside air, doesn't matter.. If the gauge reads 18psi.. .. There is a total of 18psi of air in there!
I would LOVE to dyno here at 18psi.. keep all else same, and go to Denver and dyno at.... 18psi..
I think I see a bit of humor here. you're saying, ill see less psi if I set my controller here and dont change it, and I will see less psi up there.. HA! YES of course I will.. Im saying that. Im saying, if you run 18psi up there, (No matter how you have to set the controller from different towns) 18psi up there will be almost the same as 18psi down here. Agreably a little down on power in Colorado
Just to stay clear in a very friendly way.. I never described the gauge pressure as absolute. To clear this a little further, Im describing it as the end result pressure after the turbo. Whatever the differential from the outside air, doesn't matter.. If the gauge reads 18psi.. .. There is a total of 18psi of air in there!
TOTAL gauge P (atm + boost) would be 32.7 in TX and 30.6 if they both read 18...even though both say 18, in CO you would have 6.5% less power at the same boost of 18 psi, and the turbo would be working much harder to make the 18 in CO...
2.1 psi of boost is significant...
that is not correct, 18 on the gauge in TX is NOT the same as 18 on the gauge in CO:
first, psi is not a measure of the volume of air, but rather its force
second, although you would have 18 psi on the gauge in both places, as I have shown above the same volume would not flow (total P 32.7 in TX, only 30.6 in CO), since flow Q is proportional to the sq rt of differential pressure and less air Q = less power...the pressure is what 'forces' the air into the engine...as in forced induction...
Last edited by ArthurPE; 10-29-2009 at 07:27 PM.
10-29-2009, 06:27 PM
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10-29-2009, 07:08 PM
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Bruce, one quick thought on the issue.
we should also remember that the cylinders themselves are at a lower atmosphere pressure.
So if you think about the engine w/o pressure added it would be down on power slightly due to the cylinder pressure being lower. Now when you add FI to it you are adding to an already lower power level. So if you take the std formula of doubling the power of an NA engine at 15psi then you would come up with a shortage of power compared to an engine at lower elevation.
Again IMO, not 20% but at least a decent amount of power difference would you not agree to that??
Also since we are on the subject and I have been forthright with telling that dyno figures do not necessarily equate to trap speeds. How do you feel your dyno corresponds to your trap speeds. I am not meaning this as ay type of slant on anything you have done. Just curious of your thoughts, as I feel they (any) are not really as comparable as one would like to think.
we should also remember that the cylinders themselves are at a lower atmosphere pressure.
So if you think about the engine w/o pressure added it would be down on power slightly due to the cylinder pressure being lower. Now when you add FI to it you are adding to an already lower power level. So if you take the std formula of doubling the power of an NA engine at 15psi then you would come up with a shortage of power compared to an engine at lower elevation.
Again IMO, not 20% but at least a decent amount of power difference would you not agree to that??
Also since we are on the subject and I have been forthright with telling that dyno figures do not necessarily equate to trap speeds. How do you feel your dyno corresponds to your trap speeds. I am not meaning this as ay type of slant on anything you have done. Just curious of your thoughts, as I feel they (any) are not really as comparable as one would like to think.
10-29-2009, 07:50 PM
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And yes I agree if your gauge reads absolute pressure, then 18psi in Houston is going to be the same as 18psi in Denver...
That said, you will make less power here, due to lower VE.
-Rogue
10-29-2009, 10:00 PM
#51
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the 18 psi on the gauge in CO is 20+ in Houston...
TOTAL gauge P (atm + boost) would be 32.7 in TX and 30.6 if they both read 18...even though both say 18, in CO you would have 6.5% less power at the same boost of 18 psi, and the turbo would be working much harder to make the 18 in CO...
2.1 psi of boost is significant...
that is not correct, 18 on the gauge in TX is NOT the same as 18 on the gauge in CO:
first, psi is not a measure of the volume of air, but rather its force
second, although you would have 18 psi on the gauge in both places, as I have shown above the same volume would not flow (total P 32.7 in TX, only 30.6 in CO), since flow Q is proportional to the sq rt of differential pressure and less air Q = less power...the pressure is what 'forces' the air into the engine...as in forced induction...
TOTAL gauge P (atm + boost) would be 32.7 in TX and 30.6 if they both read 18...even though both say 18, in CO you would have 6.5% less power at the same boost of 18 psi, and the turbo would be working much harder to make the 18 in CO...
2.1 psi of boost is significant...
that is not correct, 18 on the gauge in TX is NOT the same as 18 on the gauge in CO:
first, psi is not a measure of the volume of air, but rather its force
second, although you would have 18 psi on the gauge in both places, as I have shown above the same volume would not flow (total P 32.7 in TX, only 30.6 in CO), since flow Q is proportional to the sq rt of differential pressure and less air Q = less power...the pressure is what 'forces' the air into the engine...as in forced induction...
Bruce, one quick thought on the issue.
we should also remember that the cylinders themselves are at a lower atmosphere pressure.
So if you think about the engine w/o pressure added it would be down on power slightly due to the cylinder pressure being lower. Now when you add FI to it you are adding to an already lower power level. So if you take the std formula of doubling the power of an NA engine at 15psi then you would come up with a shortage of power compared to an engine at lower elevation.
Again IMO, not 20% but at least a decent amount of power difference would you not agree to that??
Also since we are on the subject and I have been forthright with telling that dyno figures do not necessarily equate to trap speeds. How do you feel your dyno corresponds to your trap speeds. I am not meaning this as ay type of slant on anything you have done. Just curious of your thoughts, as I feel they (any) are not really as comparable as one would like to think.
we should also remember that the cylinders themselves are at a lower atmosphere pressure.
So if you think about the engine w/o pressure added it would be down on power slightly due to the cylinder pressure being lower. Now when you add FI to it you are adding to an already lower power level. So if you take the std formula of doubling the power of an NA engine at 15psi then you would come up with a shortage of power compared to an engine at lower elevation.
Again IMO, not 20% but at least a decent amount of power difference would you not agree to that??
Also since we are on the subject and I have been forthright with telling that dyno figures do not necessarily equate to trap speeds. How do you feel your dyno corresponds to your trap speeds. I am not meaning this as ay type of slant on anything you have done. Just curious of your thoughts, as I feel they (any) are not really as comparable as one would like to think.
And to answer the quarter mile time/mph. Dynoed 420@wheels on a 2500lb car with driver should equate to 129mph. I ran a 124mph.. BUT 420 was corrected.. 400 was actual. - 90+deg, humidity, etc That should equal to a 127mph trap. That's only a 3mph difference that I know I lost when I left the line like I had expired tags and a warrant for my arrest while sitting next to a State trooper. It was only that one run I did because I was dying to track the car and I didn't want to hurt the transmission. I was going to run again, but the line was huge, end of night, and I was fine with the outcome. I was hoping for a little more MPH, but I knew an aggressive start would help out a lot (The 11 sec run was ran a maxchip and a 60-1hifi turbo that I never dynoed)
UGH.. Why couldn't I have been born into money.. I'm just the jackass to Dyno my setup here in Houston, put it on a trailer that day, drive to Denver to visit some Rennlisters and Dyno again.. Chart for Chart.. (only correction would be for humitidy/baro/temp - NO Altitude correction. I love that kind of real world data. Oh yeah, quarter mile Here, and one there for mph comparo.
It would then be a ... There it is.. I learn, While gloating or admitting confusion. While You learn and Gloat or admit confusion.. BUT, in the end, smiles and cheers to empirical data. And an END to any posts that didn't do a search on our new found info.
10-29-2009, 10:33 PM
#52
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maybe a time difference, but I think I said all these things above. In that it would be a SLIGHT difference in Volume because of the heat (needs more room) But not much. Saying that.. I would agree to your stated 6%.. NOT 21 to 30%!!! So in fact, you are helping my whole point that 21% or more Correction factor is ridiculous indeed.
in engineering 10% is considered significant...
actually depnding on scenario, Q (volume, NOT mass) may be higher at 5000' for the same absolute P...why:
to build the same pressure with hotter (due to greater compression) and lower density (lower atm pressure) it will take much more air, which the turbo will strive to supply...and probably can't...if you talk total P (atm + boost) it's the inverse...
that's why it's better to discuss mass flow vs volumetric...
I was not questioning your cf guess, but the fact that you interchangably use gauge, absolute and differential pressure and stated that there would be no difference in Q at SL and 5000' with 15 psi gauge pressure boost...
PV = nRT tells it all, and is not subject to negotiations...
so no, I don't agree with your reasoning nor science...
we do agree the cf is closer to 10% than 23% though
10-29-2009, 10:43 PM
#53
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http://www.scribd.com/doc/10209183/Turbocharger
a basic text on turbos
it gets interesting ~ page 32, they specifically use Denver as an example...
another good one FAA turbo engine performance guidelines
http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/list/AC%2023-8B/$FILE/Final-Part2.pdf
a basic text on turbos
it gets interesting ~ page 32, they specifically use Denver as an example...
another good one FAA turbo engine performance guidelines
http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/list/AC%2023-8B/$FILE/Final-Part2.pdf
10-30-2009, 12:15 AM
#54
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But at full throttle, the power would be close to the same at both elevations.
Remember, I didn't say both cars have the same turbos; we are saying, both are operating at the same absolute intake manifold pressure.
10-30-2009, 12:24 AM
#55
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If the car that's operating at the higher elevation has a big enough turbo creating the same absolute pressure, I would argue that the VE loss would be minimal. The turbine section needs to be efficient and flow well in order to keep turbine inlet pressure in check, however. It will be laggy, though, and that's probably the biggest detriment to the higher elevation in this case.
But at full throttle, the power would be close to the same at both elevations.
Remember, I didn't say both cars have the same turbos; we are saying, both are operating at the same absolute intake manifold pressure.
But at full throttle, the power would be close to the same at both elevations.
Remember, I didn't say both cars have the same turbos; we are saying, both are operating at the same absolute intake manifold pressure.
If so, then how about comparing a K26/6 to a GT42R. Of course one is going to flow better and not drop VE as much due to altitude. However, when comparing apples to apples, the same turbo car will lose VE due to altitude.
-Rogue
10-30-2009, 08:43 AM
#56
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no, the Q difference would not be slight, unless 10% is slight...
in engineering 10% is considered significant...
actually depnding on scenario, Q (volume, NOT mass) may be higher at 5000' for the same absolute P...why:
to build the same pressure with hotter (due to greater compression) and lower density (lower atm pressure) it will take much more air, which the turbo will strive to supply...and probably can't...if you talk total P (atm + boost) it's the inverse...
that's why it's better to discuss mass flow vs volumetric...
I was not questioning your cf guess, but the fact that you interchangably use gauge, absolute and differential pressure and stated that there would be no difference in Q at SL and 5000' with 15 psi gauge pressure boost...
PV = nRT tells it all, and is not subject to negotiations...
so no, I don't agree with your reasoning nor science...
we do agree the cf is closer to 10% than 23% though
in engineering 10% is considered significant...
actually depnding on scenario, Q (volume, NOT mass) may be higher at 5000' for the same absolute P...why:
to build the same pressure with hotter (due to greater compression) and lower density (lower atm pressure) it will take much more air, which the turbo will strive to supply...and probably can't...if you talk total P (atm + boost) it's the inverse...
that's why it's better to discuss mass flow vs volumetric...
I was not questioning your cf guess, but the fact that you interchangably use gauge, absolute and differential pressure and stated that there would be no difference in Q at SL and 5000' with 15 psi gauge pressure boost...
PV = nRT tells it all, and is not subject to negotiations...
so no, I don't agree with your reasoning nor science...
we do agree the cf is closer to 10% than 23% though
Now that I'm a little annoyed by you, (not truly upset at all) I will reverse and apologize to Rogue for being a bit of a smart *** (I can't help it sometimes) You are trying to do to me, what I think I was doing to him by saying that 18psi is 18psi. no matter what. He was just trying to say that the 18psi he sees in the manifold doesn't hold the same mass. Once again.. Apologies.. You have now exampled how annoying I must have been to him... I really do suck for that.
I now offer beers and cheers to all - yes even the geeky guy with the pocket protector above.
Sid, i'm sorry, but even though you're in Denver, your cars still ridiculously quick in your videos, and I won't budge man.. That atmosphere doesn't seem to be holding you back much! LOL.
10-30-2009, 11:20 AM
#57
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Seriously though, it is much harder to make power up here. I have always been envious of those at lower elevations.
What I have noticed over the years is that you have to overbuild to be competitive. Then, if tuned to far on the ragged edge, taking it to sea level it may go BOOM.
It truly does make it difficult to get everything right for heading out of town. I still have friends that run different heads up races all over and they are not worried at all about what the cars do up here vs at lower elevations. Just b/c it ran good at low elevation does not mean it will up here and visa versa.
The one advantage we do have up here is the lower drag (thinner air) for really fast cars. That and a nice sticky track. In top fuel and nitro classes, some records have been set here over the years. It really is about chassis and clutch tuning at those levels though, .....everyone makes power.
10-30-2009, 11:29 AM
#58
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Come-on. You aren't really trying to use two different turbos as your basis for comparison are you?
If so, then how about comparing a K26/6 to a GT42R. Of course one is going to flow better and not drop VE as much due to altitude. However, when comparing apples to apples, the same turbo car will lose VE due to altitude.
-Rogue
If so, then how about comparing a K26/6 to a GT42R. Of course one is going to flow better and not drop VE as much due to altitude. However, when comparing apples to apples, the same turbo car will lose VE due to altitude.
-Rogue
Your original statement was two cars having the same absolute intake manifold pressures; that's all.
So, I'm sayin' you could have a well engineered system, having plenty of leeway and "leftover turbo airflow" available, and you could live near sea level. Then you take a weekend trip with your girlfriend to Denver, and you will not experience any real drop in power (laggier, yes). So, the same turbo car (your words) has not lost VE due to altitude.
10-30-2009, 12:39 PM
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Your original statement was two cars having the same absolute intake manifold pressures; that's all.
So, I'm sayin' you could have a well engineered system, having plenty of leeway and "leftover turbo airflow" available, and you could live near sea level. Then you take a weekend trip with your girlfriend to Denver, and you will not experience any real drop in power (laggier, yes). So, the same turbo car (your words) has not lost VE due to altitude.
So, I'm sayin' you could have a well engineered system, having plenty of leeway and "leftover turbo airflow" available, and you could live near sea level. Then you take a weekend trip with your girlfriend to Denver, and you will not experience any real drop in power (laggier, yes). So, the same turbo car (your words) has not lost VE due to altitude.
Even a well engineered system with 'plenty of leeway' will loose VE - perhaps not as much as an undersized turbo, but regardless, it will loose some VE due to altitude. A turbo is not free energy.
What exactly are you trying to accomplish here?
10-30-2009, 03:16 PM
#60
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[QUOTE=Rogue_Ant;7031938
What exactly are you trying to accomplish here?[/QUOTE]
I merely stated that you don't necessarily lose VE going up to modestly higher elevations. Maybe it hit a nerve because it went against your statement, but it seems like you're gettin' bent all out of shape.
What exactly are you trying to accomplish here?[/QUOTE]
I merely stated that you don't necessarily lose VE going up to modestly higher elevations. Maybe it hit a nerve because it went against your statement, but it seems like you're gettin' bent all out of shape.