Boost and altitude?
10-13-2006, 03:31 PM
#42
Hey Guys
The discussion, before i posted, went into the why's and the how's, which is why i tried to be thorough. Anyway, better more info than less.... writing all this down helped me organize my own thoughts on the subject.
On to you question
Well, like i said if you tune the car only at one of those locations without using altitude correction, than your tune would be off, and that can lose you power in almost evry case (being too lean or too rich from optimal afr). Now, assuming that you car is tuned perfectly for all eventualities, perfectly with altitude compensation, and that you have an adjutable boost controlelr which TN kits don't have, then two things will happen. At the same boost setting, or in your case, same wastegate spring, of 9psi at sea level, you will develop only 5.3psi at 5000' elevation. So your power will fall by about 16% just on the account of the lower boost. However, you will also experience power loss due to less compressor efficiency, so lose another 3-4% because of that. So, roughtly 18-20% of total power.
Read the following if you want to know more:
On the account of compr efficiency change, your car would run richer, but you will also have higher intake temps (IF the temperature was the same at two elevation). It'a almost cooler at hihger elevation at a rate of 2degC per 1000', so you would have 10deg C (or 18 deg F) lower temps, which would help you (and cancel the effect of richer mixtures i just talked about if you don't have proper IAT compensation). So, in all likelihood, 93 octane would not help, sinice the coolertemps already would be a deterrant against detonation, and you would be running richer. Now, if oyu had a boost controller and turned your boost back up to 9 psi, then your mixture would be closer to what was tuned, except the compr efficiency change would be slightly higher due to the higher PR, which would still throw things off just like i discussed above, but to a greater degree. So, it all depends what kind of EMS you have, and what compensations it's got.
HTH
The discussion, before i posted, went into the why's and the how's, which is why i tried to be thorough. Anyway, better more info than less.... writing all this down helped me organize my own thoughts on the subject.
On to you question
Originally Posted by 2fast4thelaw
Somebody is gettin schooled! I love it when two power brains go at it. 
Lets cut the scientific mumbo jumbo here for a moment. Bottom line this what is really being asked.
What would be the HP difference between my stock 350Z with a ST TN kit at 5000 Plus elevation vs the same exact car at sea-level? Aproximately.
Lets cut the scientific mumbo jumbo here for a moment. Bottom line this what is really being asked.
What would be the HP difference between my stock 350Z with a ST TN kit at 5000 Plus elevation vs the same exact car at sea-level? Aproximately.
Read the following if you want to know more:
On the account of compr efficiency change, your car would run richer, but you will also have higher intake temps (IF the temperature was the same at two elevation). It'a almost cooler at hihger elevation at a rate of 2degC per 1000', so you would have 10deg C (or 18 deg F) lower temps, which would help you (and cancel the effect of richer mixtures i just talked about if you don't have proper IAT compensation). So, in all likelihood, 93 octane would not help, sinice the coolertemps already would be a deterrant against detonation, and you would be running richer. Now, if oyu had a boost controller and turned your boost back up to 9 psi, then your mixture would be closer to what was tuned, except the compr efficiency change would be slightly higher due to the higher PR, which would still throw things off just like i discussed above, but to a greater degree. So, it all depends what kind of EMS you have, and what compensations it's got.
HTH
10-13-2006, 04:00 PM
#44
Originally Posted by GurgenPB
Hey Guys
The discussion, before i posted, went into the why's and the how's, which is why i tried to be thorough. Anyway, better more info than less.... writing all this down helped me organize my own thoughts on the subject.
On to you question
Well, like i said if you tune the car only at one of those locations without using altitude correction, than your tune would be off, and that can lose you power in almost evry case (being too lean or too rich from optimal afr). Now, assuming that you car is tuned perfectly for all eventualities, perfectly with altitude compensation, and that you have an adjutable boost controlelr which TN kits don't have, then two things will happen. At the same boost setting, or in your case, same wastegate spring, of 9psi at sea level, you will develop only 5.3psi at 5000' elevation. How do you figure this? So your power will fall by about 16% just on the account of the lower boost. Why won't the wastegate compensate? Your not explaining this. That is the job of the wastegate to read manifold pressure and route exhaust gas to or from the turbo. Your not explainging that. However, you will also experience power loss due to less compressor efficiency, so lose another 3-4% because of that. So, roughtly 18-20% of total power. Explain to me why turbochharged airplanes are flat rated for a given horespower up to a given altitude. But your stating that you will lose power as altitude increases.
Read the following if you want to know more:
On the account of compr efficiency change, your car would run richer, but you will also have higher intake temps (IF the temperature was the same at two elevation). It'a almost cooler at hihger elevation at a rate of 2degC per 1000', Dry adiabatic lapse rate is 3 degrees celcius per 1000'. ICAO lapse rate which you are quoting is for an atmosphere containing ZERo moisture and is unrealistic in making real world calculations. so you would have 10deg C (or 18 deg F) lower temps, which would help you (and cancel the effect of richer mixtures i just talked about if you don't have proper IAT compensation). So, in all likelihood, 93 octane would not help, sinice the coolertemps already would be a deterrant against detonation, and you would be running richer. Now, if oyu had a boost controller and turned your boost back up to 9 psi, then your mixture would be closer to what was tuned, except the compr efficiency change would be slightly higher due to the higher PR, which would still throw things off just like i discussed above, but to a greater degree. So, it all depends what kind of EMS you have, and what compensations it's got. Let's remove the EMS from the equation which complicates things greatly and discuss manual waste gates which levels the playing field. The physics involved are the same.
If your so thorough in your explanation why didn't you include intercooler efficiency in relation to decreased density altitude. It sounds like you cut and pasted this from various page on the internet. It's completely incoherent and doesn't make much sense or make me feel like you actually have any understanding of it no matter how technical you'd like to be.
HTH
The discussion, before i posted, went into the why's and the how's, which is why i tried to be thorough. Anyway, better more info than less.... writing all this down helped me organize my own thoughts on the subject.
On to you question
Well, like i said if you tune the car only at one of those locations without using altitude correction, than your tune would be off, and that can lose you power in almost evry case (being too lean or too rich from optimal afr). Now, assuming that you car is tuned perfectly for all eventualities, perfectly with altitude compensation, and that you have an adjutable boost controlelr which TN kits don't have, then two things will happen. At the same boost setting, or in your case, same wastegate spring, of 9psi at sea level, you will develop only 5.3psi at 5000' elevation. How do you figure this? So your power will fall by about 16% just on the account of the lower boost. Why won't the wastegate compensate? Your not explaining this. That is the job of the wastegate to read manifold pressure and route exhaust gas to or from the turbo. Your not explainging that. However, you will also experience power loss due to less compressor efficiency, so lose another 3-4% because of that. So, roughtly 18-20% of total power. Explain to me why turbochharged airplanes are flat rated for a given horespower up to a given altitude. But your stating that you will lose power as altitude increases.
Read the following if you want to know more:
On the account of compr efficiency change, your car would run richer, but you will also have higher intake temps (IF the temperature was the same at two elevation). It'a almost cooler at hihger elevation at a rate of 2degC per 1000', Dry adiabatic lapse rate is 3 degrees celcius per 1000'. ICAO lapse rate which you are quoting is for an atmosphere containing ZERo moisture and is unrealistic in making real world calculations. so you would have 10deg C (or 18 deg F) lower temps, which would help you (and cancel the effect of richer mixtures i just talked about if you don't have proper IAT compensation). So, in all likelihood, 93 octane would not help, sinice the coolertemps already would be a deterrant against detonation, and you would be running richer. Now, if oyu had a boost controller and turned your boost back up to 9 psi, then your mixture would be closer to what was tuned, except the compr efficiency change would be slightly higher due to the higher PR, which would still throw things off just like i discussed above, but to a greater degree. So, it all depends what kind of EMS you have, and what compensations it's got. Let's remove the EMS from the equation which complicates things greatly and discuss manual waste gates which levels the playing field. The physics involved are the same.
If your so thorough in your explanation why didn't you include intercooler efficiency in relation to decreased density altitude. It sounds like you cut and pasted this from various page on the internet. It's completely incoherent and doesn't make much sense or make me feel like you actually have any understanding of it no matter how technical you'd like to be.
HTH
Last edited by JETPILOT; 10-13-2006 at 04:06 PM.
10-13-2006, 04:29 PM
#45
Here is an excerpt from a Socata Turbo Trinidad Pilot Operator Handbook...
Engine Performance Page 8 chapter 1
Download here: http://www.socata.eads.net/xml/conte...1/40931518.pdf
Engine rated @ 250 BHP @ 2575 RPM
*Note* The turbocharger allows to maintain this rating in standard atmosphere up to 20,000 feet.
Explain this.......
JET
Engine Performance Page 8 chapter 1
Download here: http://www.socata.eads.net/xml/conte...1/40931518.pdf
Engine rated @ 250 BHP @ 2575 RPM
*Note* The turbocharger allows to maintain this rating in standard atmosphere up to 20,000 feet.
Explain this.......
JET
Last edited by JETPILOT; 10-13-2006 at 04:51 PM.
10-13-2006, 05:15 PM
#46
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Hey JET
don't be accusing Gurgen of "cutting and pasting", that's the last thing he did
...I'm sure he'll be online to address these questions soon
Don't get nasty, this isn't a fight...it is a conversation...Gurgen is known for spending so much time trying to give imput to the community, please don't turn this into a pissing contest...
I'm willing to bet EVERY SINGLE question you have, he will answer and explain above and beyond your expectations!
-TODD
don't be accusing Gurgen of "cutting and pasting", that's the last thing he did
...I'm sure he'll be online to address these questions soonDon't get nasty, this isn't a fight...it is a conversation...Gurgen is known for spending so much time trying to give imput to the community, please don't turn this into a pissing contest...
I'm willing to bet EVERY SINGLE question you have, he will answer and explain above and beyond your expectations!
-TODD
10-13-2006, 05:16 PM
#47
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Interesting stuff,
Bottomline: Higher Elevation = Less Power which has been proven on race tracks over and over again by pros and amateurs.
Example LACR 7500 feet (air density) I would run consistent 12.4's were at Fontana at 4300 feet (air density) I would run consistent 12.1's same exact setup.
Turboed cars are not as much affected as na cars but there's definetely a power loss.
The only time I have not experienced a noticable power loss based on elevation was when I ran Nitrous.
Bottomline: Higher Elevation = Less Power which has been proven on race tracks over and over again by pros and amateurs.
Example LACR 7500 feet (air density) I would run consistent 12.4's were at Fontana at 4300 feet (air density) I would run consistent 12.1's same exact setup.
Turboed cars are not as much affected as na cars but there's definetely a power loss.
The only time I have not experienced a noticable power loss based on elevation was when I ran Nitrous.
10-13-2006, 05:33 PM
#48
Originally Posted by mrtomcat
Interesting stuff,
Bottomline: Higher Elevation = Less Power which has been proven on race tracks over and over again by pros and amateurs.
Example LACR 7500 feet (air density) I would run consistent 12.4's were at Fontana at 4300 feet (air density) I would run consistent 12.1's same exact setup.
Turboed cars are not as much affected as na cars but there's definetely a power loss.
The only time I have not experienced a noticable power loss based on elevation was when I ran Nitrous.
Bottomline: Higher Elevation = Less Power which has been proven on race tracks over and over again by pros and amateurs.
Example LACR 7500 feet (air density) I would run consistent 12.4's were at Fontana at 4300 feet (air density) I would run consistent 12.1's same exact setup.
Turboed cars are not as much affected as na cars but there's definetely a power loss.
The only time I have not experienced a noticable power loss based on elevation was when I ran Nitrous.
Do you know the density altitude for each day you ran? Pressure altitude is worthless when calculating performance. Let's look @ this from a scientific approach and use insustry accepted control factors instead of speculation. Because speculative thinking is really worthless.Sorry if I came off nasty.... didn't mean to.
It's just if you want people to understand where you are comming from don't compose an explanatyion as if you were writing an article from Scientific America. It seems like that was meant to impress rather than convince anyone of anything. I do understand these issues, and what he wrote I couldn't follow without reading it a few times.JET
Last edited by JETPILOT; 10-13-2006 at 05:40 PM.
10-13-2006, 06:07 PM
#49
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lol, my point being, science might explain it but the reality is still it is what it is....and yes, I do check the air density altitude after every event.
10-13-2006, 06:16 PM
#51
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Originally Posted by JETPILOT
Explain the reality of a turbocharged plane being able to hold flat rated power to 20,000 feet.
JET
JET
10-13-2006, 06:38 PM
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Originally Posted by JETPILOT
Explain the reality of a turbocharged plane being able to hold flat rated power to 20,000 feet.
JET
JET
Most turbocharged aircraft have the wastgate open at sea level. The WG is referenced to manifold absolute pressure (MAP), and gradually closes as the aircraft gains altitude which keeps the engines output constant with respect to the engines output in what is essentially a naturally aspirtated state at sea level. All the turbo does is keep the MAP equal to what it was at sea level.
If the turbo is well matched to the engine it should stay well within the efficient part of the compressor map, as it is being used to "normalize" output to the engine's NA sea level output, not to add substantial output above the NA power the engine can generate.
I apologize if this has already been covered, it is a long thread.
10-13-2006, 06:48 PM
#53
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Originally Posted by JETPILOT
The atmosphere is the defined volume. The atmosphere exerts 14.7psi at sea level at 29.92 hg at 59 degrees farenheit.
I can't go into the basics of atmoshperic affects on engine performance in a message group. You could find a book or video on flight physics and performance and it will explain everything to you.
Here are the facts summarized. Altitude has no effect on turbocharged engines until the wastegate has reached it's fully closed position and can no longer regulate boost. Any altitude increase at that point will decrease the power of the engine. Supercharged motors lose perfromance with altitude at the same rate a naturally aspirated motor will.
As altitude increases the wastegate regulates 8psi of turbo boost by opening later and dumping less exhaust. Due to the thinner air of the atmoshere as altitude increases the compressor encounters less resistance/friction from the thinner air and spins faster to create the same amount of boost.
JET
I can't go into the basics of atmoshperic affects on engine performance in a message group. You could find a book or video on flight physics and performance and it will explain everything to you.
Here are the facts summarized. Altitude has no effect on turbocharged engines until the wastegate has reached it's fully closed position and can no longer regulate boost. Any altitude increase at that point will decrease the power of the engine. Supercharged motors lose perfromance with altitude at the same rate a naturally aspirated motor will.
As altitude increases the wastegate regulates 8psi of turbo boost by opening later and dumping less exhaust. Due to the thinner air of the atmoshere as altitude increases the compressor encounters less resistance/friction from the thinner air and spins faster to create the same amount of boost.
JET
10-13-2006, 07:28 PM
#54
As I stated in ome of my previous posts.... a turbocharged car will maintain sea level power until the wastegate is completely closed. Please read my previous posts before posting a counter point that I already covered.
JET
JET
Last edited by JETPILOT; 10-13-2006 at 07:34 PM.
10-13-2006, 07:32 PM
#55
Originally Posted by plumpzz
False. Boost guage measure guage pressure. If atmospheric pressure decreases, it'll still read the same as at ocean but the entire system will be working harder. Just because low pressure air is easier to compress doesn't mean it'll compress more.
I have no idea what "boost gauge measures gauge pressure" means.
What am I wrong about?
JET
10-13-2006, 07:38 PM
#56
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Sorry i didnt read one of your posts. The wastegate will open later, which you are right about. However, the engine and turbo are working harder due to different efficiency zones and decreased air density. The guage will always read the psi you're tuned for exactly for that reason. However, if you are running 10psi in a 14 psi environemtn, your absolute pressure is 24psi. If you are running '10 guage pressure' in a 12 psi environment, you're actually running 22 absolute pressure. What this means is that if you are running less absolute boost, which is techincally more important than guage boost. You are at the end making less power, you're making 22/24 of the power you should (since compression engines depend on well..compression). This would explain why NA engines suffer more in high altitudes. They run at absolute boost of atmospheric pressure. If you are in a 12psi environemtn, you're running 12/14 of power at ocean lvl.
10-13-2006, 07:46 PM
#57
But the atmospheric environment shouldn't be a factor since the wastegate is reading off of MAP which is a closed environent. All the WG knows is the MAP and the spring or BC are set for and will regulate the boost to hold whatever PSI is selected regardless of atmospheric pressure.
JET
JET
10-13-2006, 07:47 PM
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Originally Posted by JETPILOT
As I stated in ome of my previous posts.... a turbocharged car will maintain sea level power until the wastegate is completely closed. Please read my previous posts before posting a counter point that I already covered.
JET
JET
10-13-2006, 07:51 PM
#59
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Manifold absolute pressure isn't closed off. At idle, its at vacuum. If there was no turbocharger, then at 100% throttle its at atmospheric pressure. When its under boost, its at atmospheric pressure + pressure at turbo - pressure lost in piping. Wastegate runs off a spring which is set off once pressure reaches a certain psi. If atmospheric pressure is less, the turbo will compensate to reach teh same guage boost (boost read at boost guage). This doesn't mean however that absolute pressure will remain the same, because atmospheric pressure dropped. If the spring is set at 8psi, the turbo will boost the engine only after 0 psi is acheived in the manifold, so it will still go off at 8psi.
WG is independant of atmospheric pressure. However, absolute pressure is what determines the output of the engine. This is in an ideal engine btw. At higher altitudes, compression is much greater so more heat will be generated for the same pressure....ect blah blah.
WG is independant of atmospheric pressure. However, absolute pressure is what determines the output of the engine. This is in an ideal engine btw. At higher altitudes, compression is much greater so more heat will be generated for the same pressure....ect blah blah.
10-13-2006, 07:59 PM
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Originally Posted by JETPILOT
As I stated in ome of my previous posts.... a turbocharged car will maintain sea level power until the wastegate is completely closed. Please read my previous posts before posting a counter point that I already covered.
JET
JET