Boost and altitude (searched+read faq)
01-03-2005, 06:28 PM
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Boost and altitude (searched+read faq)
I've already searched and I did'nt find an answer, I'd be really happy if someone answered my questions.
Since atmospheric pressure is 14.7 at sea level and more like 11.7 at 5,000 Ft elevation, would'nt the first 3 PSI of boost go to waste? Well, not go to waste, but if you're somewhere where the atmosphereic pressure is 11.7, would'nt the first 3psi of boost do nothing but fix the elevation differeance (while adding power)
I have another question, theres this 'rule of thumb' I heard about that says you lose %3 of power for every 1000FT of altitude, do you guys think this is true?
My third question, let's say you have a 100 HP all motor engine and you go to a really high altitude, high enough that your engine makes more like 70 HP... if you boosted your motor to add only 30 HP and ended up having 100 HP at that high altitude, would the engine be reliable as stock since it's making only 100 HP?
EDIT: I'm not 100% sure if atmospheric pressure at 5000FT is 11.7, so if you know the correct pressure, please correct me.
Since atmospheric pressure is 14.7 at sea level and more like 11.7 at 5,000 Ft elevation, would'nt the first 3 PSI of boost go to waste? Well, not go to waste, but if you're somewhere where the atmosphereic pressure is 11.7, would'nt the first 3psi of boost do nothing but fix the elevation differeance (while adding power)
I have another question, theres this 'rule of thumb' I heard about that says you lose %3 of power for every 1000FT of altitude, do you guys think this is true?
My third question, let's say you have a 100 HP all motor engine and you go to a really high altitude, high enough that your engine makes more like 70 HP... if you boosted your motor to add only 30 HP and ended up having 100 HP at that high altitude, would the engine be reliable as stock since it's making only 100 HP?
EDIT: I'm not 100% sure if atmospheric pressure at 5000FT is 11.7, so if you know the correct pressure, please correct me.
01-04-2005, 09:02 AM
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Re: Boost and altitude (JoeD427)
Im no expert but the 3 psi of boost going to "waste" seems right. Your going to make power with any properly boosted motor on 3 psi or 30 psi of boost, you just start at a lower hp number because of elevation difference.
It is true that you do lose horsepower through elevation, think about it, at sea level your sucking in 14.7 ATM. and at say 5000 ft your at 11.7 ATM. you can add more fuel at 14.7 because the air is denser and you would need that extra fuel to keep the AFR right.
Dont quote me on this, just putting common sense together at best. But lets keep this on the first page, this info will benefit all of us.
Jon
It is true that you do lose horsepower through elevation, think about it, at sea level your sucking in 14.7 ATM. and at say 5000 ft your at 11.7 ATM. you can add more fuel at 14.7 because the air is denser and you would need that extra fuel to keep the AFR right.
Dont quote me on this, just putting common sense together at best. But lets keep this on the first page, this info will benefit all of us.
Jon
01-04-2005, 09:21 AM
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Re: Boost and altitude (Raf)
The issues that you raise in your post are very valid and of great concern to a particular group of vehicle operators--pilots. As a piston powered aircraft climbs it actually loses power because of the reduced air pressure.
First off, pressure is not the only factor. Temperature also plays a role. The reason why superchargers (and I use this term to include "turbochargers") work is not because of the increase of pressure, but due to the increased density. Packing more air into your engine causes more oxygen to be packed in and, therefore, you can burn more fuel with each powere stroke. Temperature, in addition to pressure, affects air density. On hot days the engine will not perform as well as on cold days. (In fact, with aircraft, the outside air temperature may be the difference between getting off of a short runway or not.)
This link shows a table that gives standard atmospheric pressures at various altitudes at standard temperature (defined to be 15 deg C at mean sea level). It shows that standard pressure at sea level is 14.696 PSIA and at 5,000 feet is 12.23 PSIA.
So if you had an engine that was boosted by 2.466 PSI and that engine was operating at 5,000 feet above sea level then the engine would behave as if it is at sea level. This is to say that the boost would compensate for the lost power caused by the raised elevation as compared to operating at sea level and the engine internals would not experience any stress greater than that at sea level.
I have never heard of the 3% rule that you state so I can neither confirm nor deny the accuracy of this approximation.
Here is another web page that talks about high altitude supercharging. You will notice that this page talks about using a Whipple supercharger rather than a turbocharger for high altitude. There is a problem with turbos at high altitude, the reduced air resistance causes the turbo to overspeed. When this happens it can generate what is called a "compressor stall"--the air is no longer flowing smoothly over the compressor blades and the pressure on the back side may even be greater than the pressure on the front side of the comressor (causing air to flow the wrong way through the conpressor).
Hope that helped....
First off, pressure is not the only factor. Temperature also plays a role. The reason why superchargers (and I use this term to include "turbochargers") work is not because of the increase of pressure, but due to the increased density. Packing more air into your engine causes more oxygen to be packed in and, therefore, you can burn more fuel with each powere stroke. Temperature, in addition to pressure, affects air density. On hot days the engine will not perform as well as on cold days. (In fact, with aircraft, the outside air temperature may be the difference between getting off of a short runway or not.)
This link shows a table that gives standard atmospheric pressures at various altitudes at standard temperature (defined to be 15 deg C at mean sea level). It shows that standard pressure at sea level is 14.696 PSIA and at 5,000 feet is 12.23 PSIA.
So if you had an engine that was boosted by 2.466 PSI and that engine was operating at 5,000 feet above sea level then the engine would behave as if it is at sea level. This is to say that the boost would compensate for the lost power caused by the raised elevation as compared to operating at sea level and the engine internals would not experience any stress greater than that at sea level.
I have never heard of the 3% rule that you state so I can neither confirm nor deny the accuracy of this approximation.
Here is another web page that talks about high altitude supercharging. You will notice that this page talks about using a Whipple supercharger rather than a turbocharger for high altitude. There is a problem with turbos at high altitude, the reduced air resistance causes the turbo to overspeed. When this happens it can generate what is called a "compressor stall"--the air is no longer flowing smoothly over the compressor blades and the pressure on the back side may even be greater than the pressure on the front side of the comressor (causing air to flow the wrong way through the conpressor).
Hope that helped....
01-04-2005, 09:40 AM
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Re: Boost and altitude (mct121)
ok back to the subject. if you are pushing 3psi on your boost guage in FL. on a standard day (15deg. C and 14.7/ 29.92") or you are pushing 3psi in colorado you will have almost the same performance. The only difference is the turbo will be "working harder" to make the 3 psi due to less pressure/density. BTW i am a pilot, i just came home from class (CFI-I). more... if you have a n/a car in fl and you have a boost guage on it (attached to you mani) when you start the car it will read negative (at idle) when you go WOT it will go to standard pressure ie the air will equalize from inside and outside the mani./throttle body. so now you go to colorado and do the same thing and your boost guage will read slightly lower at WOT. soooo if you push 3psi the turbo will still push 3 psi but will have to build a little "boost" just to get back to standard. so again boost at 3psi is the same wherever you are, it doesn't cancel out or anything like that.
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01-04-2005, 09:48 AM
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Re: Boost and altitude (incredteg3)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by incredteg3 »</TD></TR><TR><TD CLASS="quote"> if you have a n/a car in fl and you have a boost guage on it (attached to you mani) when you start the car it will read negative (at idle) when you go WOT it will go to standard pressure ie the air will equalize from inside and outside the mani./throttle body. so now you go to colorado and do the same thing and your boost guage will read slightly lower at WOT. </TD></TR></TABLE>
No it wont, because a boost gauge references from the current atmospheric pressure. You would need an absolute pressure gauge instead of a standard boost gauge to see that.
No it wont, because a boost gauge references from the current atmospheric pressure. You would need an absolute pressure gauge instead of a standard boost gauge to see that.
01-04-2005, 09:55 AM
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Re: Boost and altitude (Raf)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Raf »</TD></TR><TR><TD CLASS="quote"> Since atmospheric pressure is 14.7 at sea level and more like 11.7 at 5,000 Ft elevation, would'nt the first 3 PSI of boost go to waste? Well, not go to waste, but if you're somewhere where the atmosphereic pressure is 11.7, would'nt the first 3psi of boost do nothing but fix the elevation differeance (while adding power) </TD></TR></TABLE>
No, it wouldn't go to waste, because all the N/A cars will have 3psi less air to use, so relative to them you'll still be faster.
The best way to compensate for elevation change would be to use a MAP sensor to control boost. That way you are referencing Absolute Pressure instead of Gauge Pressure to set boost. That way, when you climb in evelvation you'll actually get better performance since there will be less back pressure on the exhuast system.
No, it wouldn't go to waste, because all the N/A cars will have 3psi less air to use, so relative to them you'll still be faster.
The best way to compensate for elevation change would be to use a MAP sensor to control boost. That way you are referencing Absolute Pressure instead of Gauge Pressure to set boost. That way, when you climb in evelvation you'll actually get better performance since there will be less back pressure on the exhuast system.
01-04-2005, 02:49 PM
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Re: Boost and altitude (Marauder)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Marauder »</TD></TR><TR><TD CLASS="quote">
No it wont, because a boost gauge references from the current atmospheric pressure. You would need an absolute pressure gauge instead of a standard boost gauge to see that.</TD></TR></TABLE>
what??? yes it will you said it "current atmospheric pressure" thats going to be different at sea level verses 5,000 feet. when i say boost guage i mean one that has vacume then 0 then boost. whatever you use it will show it.
Marauder i think you need to do some more reading before you post **** saying other people are wrong when you are.
your other post is wrong aswell. at higher elevations the guy with boost will actually be like he is pushing 6psi relative to the N/A guy. this is due to the waste gate opening when it feels 3psi. i quarantee your waste gate won't open earlier due to the less atmospheric pressure. and when you say guage pressure WTF you are going to hook up your guage to you manifold and probably you boost controller too so however you want to say it what ever.
ps. i hope i wasn't a dick but people that want to learn new **** have to hear you tell the people who are right that they are wrong. and that just makes people not know what to believe. Just think before you post please.
No it wont, because a boost gauge references from the current atmospheric pressure. You would need an absolute pressure gauge instead of a standard boost gauge to see that.</TD></TR></TABLE>
what??? yes it will you said it "current atmospheric pressure" thats going to be different at sea level verses 5,000 feet. when i say boost guage i mean one that has vacume then 0 then boost. whatever you use it will show it.
Marauder i think you need to do some more reading before you post **** saying other people are wrong when you are.
your other post is wrong aswell. at higher elevations the guy with boost will actually be like he is pushing 6psi relative to the N/A guy. this is due to the waste gate opening when it feels 3psi. i quarantee your waste gate won't open earlier due to the less atmospheric pressure. and when you say guage pressure WTF you are going to hook up your guage to you manifold and probably you boost controller too so however you want to say it what ever.
ps. i hope i wasn't a dick but people that want to learn new **** have to hear you tell the people who are right that they are wrong. and that just makes people not know what to believe. Just think before you post please.
01-04-2005, 03:00 PM
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Re: Boost and altitude (incredteg3)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by incredteg3 »</TD></TR><TR><TD CLASS="quote">what??? yes it will you said it "current atmospheric pressure" thats going to be different at sea level verses 5,000 feet. when i say boost guage i mean one that has vacume then 0 then boost. whatever you use it will show it. </TD></TR></TABLE>
The problem with your example is that the NA car in CO will have a boost gauge reading of 0 psi/no vacuum when it is at WOT, not reading less. Now, if the boost gauge is sealed and has 14.7 psi of air in it, then yes, it will read less, although I think most mechanical gauges reference atmospheric pressure.
You guys are also forgetting that turbos are not positive displacement "blowers." They compress the air, so they operate on pressure ratios(or PR). Going from 14 psia atmo. to 24 psia(which would be read as 10 psi on your boost gauge) is a PR of 1.71, while going from 12 psia atmospheric to 24 psia is a PR of 2. So if the compressor can handle it, it'll compress the air to the same pressure. Yet if you insist on "pressure targets" (which I don't really like) of say "I want 10 psi" - then the guy at sea level will have 24.7 psia of pressure in his engine, and the guy in Colorado will have 2.466 psi less, or about 22.2 psia. In effect, it's almost like turning the boost down a bit. This is why they only sell 91 octane in really high altitude states - on even really high compression ratio NA engines, you just don't get nearly as much cylinder pressure as at sea level, so you don't have a detonation problem.
The problem with your example is that the NA car in CO will have a boost gauge reading of 0 psi/no vacuum when it is at WOT, not reading less. Now, if the boost gauge is sealed and has 14.7 psi of air in it, then yes, it will read less, although I think most mechanical gauges reference atmospheric pressure.
You guys are also forgetting that turbos are not positive displacement "blowers." They compress the air, so they operate on pressure ratios(or PR). Going from 14 psia atmo. to 24 psia(which would be read as 10 psi on your boost gauge) is a PR of 1.71, while going from 12 psia atmospheric to 24 psia is a PR of 2. So if the compressor can handle it, it'll compress the air to the same pressure. Yet if you insist on "pressure targets" (which I don't really like) of say "I want 10 psi" - then the guy at sea level will have 24.7 psia of pressure in his engine, and the guy in Colorado will have 2.466 psi less, or about 22.2 psia. In effect, it's almost like turning the boost down a bit. This is why they only sell 91 octane in really high altitude states - on even really high compression ratio NA engines, you just don't get nearly as much cylinder pressure as at sea level, so you don't have a detonation problem.
01-04-2005, 03:02 PM
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Re: Boost and altitude (incredteg3)
A boost gauge will reference the outside air pressure. So at WOT, the gauge will always read "0" no matter what elevation you are at.
At sea level = 14.7 psi absolute, WOT gauge reading = 0
5000 ft. = 12.2 psi absolute, WOT gauge reading = 0
At sea level = 14.7 psi absolute, WOT gauge reading = 0
5000 ft. = 12.2 psi absolute, WOT gauge reading = 0
01-04-2005, 03:05 PM
#14
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Re: Boost and altitude (incredteg3)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by incredteg3 »</TD></TR><TR><TD CLASS="quote">
Marauder i think you need to do some more reading before you post **** saying other people are wrong when you are.
your other post is wrong aswell. at higher elevations the guy with boost will actually be like he is pushing 6psi relative to the N/A guy. this is due to the waste gate opening when it feels 3psi. i quarantee your waste gate won't open earlier due to the less atmospheric pressure. and when you say guage pressure WTF you are going to hook up your guage to you manifold and probably you boost controller too so however you want to say it what ever.
ps. i hope i wasn't a dick but people that want to learn new **** have to hear you tell the people who are right that they are wrong. and that just makes people not know what to believe. Just think before you post please. </TD></TR></TABLE>
LMAO...go do YOUR homework! I think you are assuming people with turbo setups are running off of ABSOLUTE pressure. Ever basic turbo setup is all run off of gauge pressure, meaning it references the outside air pressure.
I know what I am saying, go do your homework.
Marauder i think you need to do some more reading before you post **** saying other people are wrong when you are.
your other post is wrong aswell. at higher elevations the guy with boost will actually be like he is pushing 6psi relative to the N/A guy. this is due to the waste gate opening when it feels 3psi. i quarantee your waste gate won't open earlier due to the less atmospheric pressure. and when you say guage pressure WTF you are going to hook up your guage to you manifold and probably you boost controller too so however you want to say it what ever.
ps. i hope i wasn't a dick but people that want to learn new **** have to hear you tell the people who are right that they are wrong. and that just makes people not know what to believe. Just think before you post please. </TD></TR></TABLE>
LMAO...go do YOUR homework! I think you are assuming people with turbo setups are running off of ABSOLUTE pressure. Ever basic turbo setup is all run off of gauge pressure, meaning it references the outside air pressure.
I know what I am saying, go do your homework.
01-04-2005, 05:55 PM
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Re: Boost and altitude (Marauder)
Thanks for all the answers guys. I did'nt FULLY understand everything...I'm still letting it sink in, but I wanna ask a question before I forget...
I've heard from alot of other people that the turbo will work harder to get the same pressure like incredted3 said, can I fix this problem by having the wastegate fully shut until it gets to my desired boost level and then have it open then? I"m not sure, but I think the wastegate starts opening before the turbo gets full boost, is this right? Can you guys clue me in on this?
Also, I was playing with a compression/elevation calculator and found out that when you're at sea level 10.0:1 compression ratio stays 10.0:1, but at 5000 FT the engine compresses the amount of dense air that 9.0:1 pistons would compress and changing the pistons to 11.0:1 would level things out (back to 10.0:1). What do you guys think about this?
I appreciate all the replies.
Modified by Raf at 7:05 PM 1/4/2005
I've heard from alot of other people that the turbo will work harder to get the same pressure like incredted3 said, can I fix this problem by having the wastegate fully shut until it gets to my desired boost level and then have it open then? I"m not sure, but I think the wastegate starts opening before the turbo gets full boost, is this right? Can you guys clue me in on this?
Also, I was playing with a compression/elevation calculator and found out that when you're at sea level 10.0:1 compression ratio stays 10.0:1, but at 5000 FT the engine compresses the amount of dense air that 9.0:1 pistons would compress and changing the pistons to 11.0:1 would level things out (back to 10.0:1). What do you guys think about this?
I appreciate all the replies.
Modified by Raf at 7:05 PM 1/4/2005
01-05-2005, 08:00 AM
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Re: Boost and altitude (Raf)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Raf »</TD></TR><TR><TD CLASS="quote">Also, I was playing with a compression/elevation calculator and found out that when you're at sea level 10.0:1 compression ratio stays 10.0:1, but at 5000 FT the engine compresses the amount of dense air that 9.0:1 pistons would compress and changing the pistons to 11.0:1 would level things out (back to 10.0:1). What do you guys think about this?</TD></TR></TABLE>
I will admit that I may be a little out of my expertise here, but what I think you are saying is that if I do a compression test on my engine at sea level and compare the results to a compression test done on the same engine at a high altitude that I would notice the pressure in the cylinders at sea level will be higher than the pressure in the cylinders at altitude. I agree with this statement.
I also think you are saying that you could compensate for this lower cylinder pressure in an NA engine by increasing the compression ratio. I am not sure I agree with this. I don't think that you would get the same performance as you would from the engine with the lower compression ratio at sea level. Both engines would take in about the same amount of air by volume, but the high altitude engine would have less oxygen and therefore demand less fuel. The energy generated during the power stroke comes from buring fuel so the engine with less fuel, even with the same cylinder pressure, will produce less power with each cycle.
If I am way off base here I am open to hear other, reasoned, opinions.
I will admit that I may be a little out of my expertise here, but what I think you are saying is that if I do a compression test on my engine at sea level and compare the results to a compression test done on the same engine at a high altitude that I would notice the pressure in the cylinders at sea level will be higher than the pressure in the cylinders at altitude. I agree with this statement.
I also think you are saying that you could compensate for this lower cylinder pressure in an NA engine by increasing the compression ratio. I am not sure I agree with this. I don't think that you would get the same performance as you would from the engine with the lower compression ratio at sea level. Both engines would take in about the same amount of air by volume, but the high altitude engine would have less oxygen and therefore demand less fuel. The energy generated during the power stroke comes from buring fuel so the engine with less fuel, even with the same cylinder pressure, will produce less power with each cycle.
If I am way off base here I am open to hear other, reasoned, opinions.
01-05-2005, 10:04 AM
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Re: Boost and altitude (Raf)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Raf »</TD></TR><TR><TD CLASS="quote"> I've heard from alot of other people that the turbo will work harder to get the same pressure like incredted3 said, can I fix this problem by having the wastegate fully shut until it gets to my desired boost level and then have it open then? I"m not sure, but I think the wastegate starts opening before the turbo gets full boost, is this right? Can you guys clue me in on this?</TD></TR></TABLE>
The wastegate idea you had doesnt seem possible. If im not mistaken, the Wastegate opens gradually, it doesnt open when you hit you desired boost. I believe the wastegate begins to bleed exhaust when it see any amount of positive pressure, even one lb. of boost. I think if it were to open like you stated, you would get boost spike.
Ive never had any external gate experience so dont quote me on this, just my understanding of what I have read on HT.
Jon
Modified by shadow103rd at 11:14 AM 1/5/2005
01-05-2005, 10:15 AM
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Re: Boost and altitude (Raf)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Raf »</TD></TR><TR><TD CLASS="quote">I've already searched and I did'nt find an answer, I'd be really happy if someone answered my questions.
Since atmospheric pressure is 14.7 at sea level and more like 11.7 at 5,000 Ft elevation, would'nt the first 3 PSI of boost go to waste? Well, not go to waste, but if you're somewhere where the atmosphereic pressure is 11.7, would'nt the first 3psi of boost do nothing but fix the elevation differeance (while adding power)
I have another question, theres this 'rule of thumb' I heard about that says you lose %3 of power for every 1000FT of altitude, do you guys think this is true?
My third question, let's say you have a 100 HP all motor engine and you go to a really high altitude, high enough that your engine makes more like 70 HP... if you boosted your motor to add only 30 HP and ended up having 100 HP at that high altitude, would the engine be reliable as stock since it's making only 100 HP?
EDIT: I'm not 100% sure if atmospheric pressure at 5000FT is 11.7, so if you know the correct pressure, please correct me.</TD></TR></TABLE>
You are right....
Since atmospheric pressure is 14.7 at sea level and more like 11.7 at 5,000 Ft elevation, would'nt the first 3 PSI of boost go to waste? Well, not go to waste, but if you're somewhere where the atmosphereic pressure is 11.7, would'nt the first 3psi of boost do nothing but fix the elevation differeance (while adding power)
I have another question, theres this 'rule of thumb' I heard about that says you lose %3 of power for every 1000FT of altitude, do you guys think this is true?
My third question, let's say you have a 100 HP all motor engine and you go to a really high altitude, high enough that your engine makes more like 70 HP... if you boosted your motor to add only 30 HP and ended up having 100 HP at that high altitude, would the engine be reliable as stock since it's making only 100 HP?
EDIT: I'm not 100% sure if atmospheric pressure at 5000FT is 11.7, so if you know the correct pressure, please correct me.</TD></TR></TABLE>
You are right....
01-09-2005, 05:26 PM
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Re: Boost and altitude (CivicEJ1)
This is the most correct post so far.
NHRA makes a correction factor sheet (index) which will allow people at high altitudes to figure out what they'd run at sea level. If you read the fine print of the index is says it is not accurate for forced induction engines. That's because like incredteg says, the waste gate will hold the wastegate a little longer till the boost pressure it wants is met. Supercharged engines should suffer a little but not as much as N/A engines.
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by incredteg3 »</TD></TR><TR><TD CLASS="quote">ok back to the subject. if you are pushing 3psi on your boost guage in FL. on a standard day (15deg. C and 14.7/ 29.92") or you are pushing 3psi in colorado you will have almost the same performance. The only difference is the turbo will be "working harder" to make the 3 psi due to less pressure/density. BTW i am a pilot, i just came home from class (CFI-I). more... if you have a n/a car in fl and you have a boost guage on it (attached to you mani) when you start the car it will read negative (at idle) when you go WOT it will go to standard pressure ie the air will equalize from inside and outside the mani./throttle body. so now you go to colorado and do the same thing and your boost guage will read slightly lower at WOT. soooo if you push 3psi the turbo will still push 3 psi but will have to build a little "boost" just to get back to standard. so again boost at 3psi is the same wherever you are, it doesn't cancel out or anything like that. </TD></TR></TABLE>
NHRA makes a correction factor sheet (index) which will allow people at high altitudes to figure out what they'd run at sea level. If you read the fine print of the index is says it is not accurate for forced induction engines. That's because like incredteg says, the waste gate will hold the wastegate a little longer till the boost pressure it wants is met. Supercharged engines should suffer a little but not as much as N/A engines.
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by incredteg3 »</TD></TR><TR><TD CLASS="quote">ok back to the subject. if you are pushing 3psi on your boost guage in FL. on a standard day (15deg. C and 14.7/ 29.92") or you are pushing 3psi in colorado you will have almost the same performance. The only difference is the turbo will be "working harder" to make the 3 psi due to less pressure/density. BTW i am a pilot, i just came home from class (CFI-I). more... if you have a n/a car in fl and you have a boost guage on it (attached to you mani) when you start the car it will read negative (at idle) when you go WOT it will go to standard pressure ie the air will equalize from inside and outside the mani./throttle body. so now you go to colorado and do the same thing and your boost guage will read slightly lower at WOT. soooo if you push 3psi the turbo will still push 3 psi but will have to build a little "boost" just to get back to standard. so again boost at 3psi is the same wherever you are, it doesn't cancel out or anything like that. </TD></TR></TABLE>
01-12-2005, 07:18 PM
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Re: Boost and altitude (mct121)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mct121 »</TD></TR><TR><TD CLASS="quote">
I will admit that I may be a little out of my expertise here, but what I think you are saying is that if I do a compression test on my engine at sea level and compare the results to a compression test done on the same engine at a high altitude that I would notice the pressure in the cylinders at sea level will be higher than the pressure in the cylinders at altitude. I agree with this statement.
I also think you are saying that you could compensate for this lower cylinder pressure in an NA engine by increasing the compression ratio. I am not sure I agree with this. I don't think that you would get the same performance as you would from the engine with the lower compression ratio at sea level. Both engines would take in about the same amount of air by volume, but the high altitude engine would have less oxygen and therefore demand less fuel. The energy generated during the power stroke comes from buring fuel so the engine with less fuel, even with the same cylinder pressure, will produce less power with each cycle.
If I am way off base here I am open to hear other, reasoned, opinions.
</TD></TR></TABLE>
Then how come you gain HP at sea level if you increase CP? If you go up 5000ft and increase your CP until you're at the HP level that you would be at if it was sea level, then would'nt the engine pretty much cancel everything out and think it's stock.
If the air at 5000FT is 12.2psi then would'nt the fuel system be under less stress? Let's say the air is 12.2 psi, and you boost 2.5 PSI to get back up to 14.7, since the fuel system is designed to be good enough for 14.7 PSi of air, would'nt the fuel system do just fine and have no need for upgrades? Ignore the MAP reading and asume it does'nt need adjustments because it's running a hack.
With incredteg3's theory, a turbo engine does'nt lose power because the wastegate won't open until it sees a set boost level, so it always "crams" the same amount of ait into an engine...does this mean that a turbo engine does'nt give a crap about elevation and will perform the same at any altitude? And yes, I understand the engines gona have more lag...I don't care, asume the engine gonna be running an open exaust
I'm still a little lost here about boost pressure and altitude
I will admit that I may be a little out of my expertise here, but what I think you are saying is that if I do a compression test on my engine at sea level and compare the results to a compression test done on the same engine at a high altitude that I would notice the pressure in the cylinders at sea level will be higher than the pressure in the cylinders at altitude. I agree with this statement.
I also think you are saying that you could compensate for this lower cylinder pressure in an NA engine by increasing the compression ratio. I am not sure I agree with this. I don't think that you would get the same performance as you would from the engine with the lower compression ratio at sea level. Both engines would take in about the same amount of air by volume, but the high altitude engine would have less oxygen and therefore demand less fuel. The energy generated during the power stroke comes from buring fuel so the engine with less fuel, even with the same cylinder pressure, will produce less power with each cycle.
If I am way off base here I am open to hear other, reasoned, opinions.
</TD></TR></TABLE>
Then how come you gain HP at sea level if you increase CP? If you go up 5000ft and increase your CP until you're at the HP level that you would be at if it was sea level, then would'nt the engine pretty much cancel everything out and think it's stock.
If the air at 5000FT is 12.2psi then would'nt the fuel system be under less stress? Let's say the air is 12.2 psi, and you boost 2.5 PSI to get back up to 14.7, since the fuel system is designed to be good enough for 14.7 PSi of air, would'nt the fuel system do just fine and have no need for upgrades? Ignore the MAP reading and asume it does'nt need adjustments because it's running a hack.
With incredteg3's theory, a turbo engine does'nt lose power because the wastegate won't open until it sees a set boost level, so it always "crams" the same amount of ait into an engine...does this mean that a turbo engine does'nt give a crap about elevation and will perform the same at any altitude? And yes, I understand the engines gona have more lag...I don't care, asume the engine gonna be running an open exaust
I'm still a little lost here about boost pressure and altitude
01-13-2005, 10:25 AM
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Re: Boost and altitude (Raf)
I think you guys are missing the point of why power levels go down as you go higher.
There is less oxygen at higher altitudes.
That's why some athletes train up there. That's why you have to hike all the way up Mt Everest because if you just land a helicopter near the top you couldn't do any climbing because you'd be too weak.
The blower or turbo will push enough air in to compensate.
That's why there are motorcycle shops that will remove your aircleaner so your bike can go over the rocky mountains. The loss is most felt on carburated engines because they can't compansate for high altitudes' less oxygen. The carb still adds as much fuel as it normally would but the oxygen isn't there so the ratio is rich and the power goes down. That's why you used to be able to buy high altitude cars back when they had carbs on them. Fuel injected cars can see the alt because they have a sensor that looks for it, usually the map and they have an O2. It will adjust the fuel out so the ratio is correct, power still goes down but not as much.
It's also important to remember where blowers and turbos came from, aircrafts that were trying to gain more altitude. They couldn't climb any higher because they didn't have the power. With the forced induction they could get higher than their enemies. That's where nitrous came from too.
There is less oxygen at higher altitudes.
That's why some athletes train up there. That's why you have to hike all the way up Mt Everest because if you just land a helicopter near the top you couldn't do any climbing because you'd be too weak.
The blower or turbo will push enough air in to compensate.
That's why there are motorcycle shops that will remove your aircleaner so your bike can go over the rocky mountains. The loss is most felt on carburated engines because they can't compansate for high altitudes' less oxygen. The carb still adds as much fuel as it normally would but the oxygen isn't there so the ratio is rich and the power goes down. That's why you used to be able to buy high altitude cars back when they had carbs on them. Fuel injected cars can see the alt because they have a sensor that looks for it, usually the map and they have an O2. It will adjust the fuel out so the ratio is correct, power still goes down but not as much.
It's also important to remember where blowers and turbos came from, aircrafts that were trying to gain more altitude. They couldn't climb any higher because they didn't have the power. With the forced induction they could get higher than their enemies. That's where nitrous came from too.
01-13-2005, 04:44 PM
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Re: Boost and altitude (JohnnieChimpo)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JohnnieChimpo »</TD></TR><TR><TD CLASS="quote">I think you guys are missing the point of why power levels go down as you go higher.
There is less oxygen at higher altitudes.
That's why some athletes train up there. That's why you have to hike all the way up Mt Everest because if you just land a helicopter near the top you couldn't do any climbing because you'd be too weak.
The blower or turbo will push enough air in to compensate.
That's why there are motorcycle shops that will remove your aircleaner so your bike can go over the rocky mountains. The loss is most felt on carburated engines because they can't compansate for high altitudes' less oxygen. The carb still adds as much fuel as it normally would but the oxygen isn't there so the ratio is rich and the power goes down. That's why you used to be able to buy high altitude cars back when they had carbs on them. Fuel injected cars can see the alt because they have a sensor that looks for it, usually the map and they have an O2. It will adjust the fuel out so the ratio is correct, power still goes down but not as much.
It's also important to remember where blowers and turbos came from, aircrafts that were trying to gain more altitude. They couldn't climb any higher because they didn't have the power. With the forced induction they could get higher than their enemies. That's where nitrous came from too. </TD></TR></TABLE>
Yes, I agree with this, I was just trying to get second opinions to incredteg3's theory (or fact, I dunno) that a turbo is'nt affected at altitude because the wastegate always opens when it sees a preset boost level.
There is less oxygen at higher altitudes.
That's why some athletes train up there. That's why you have to hike all the way up Mt Everest because if you just land a helicopter near the top you couldn't do any climbing because you'd be too weak.
The blower or turbo will push enough air in to compensate.
That's why there are motorcycle shops that will remove your aircleaner so your bike can go over the rocky mountains. The loss is most felt on carburated engines because they can't compansate for high altitudes' less oxygen. The carb still adds as much fuel as it normally would but the oxygen isn't there so the ratio is rich and the power goes down. That's why you used to be able to buy high altitude cars back when they had carbs on them. Fuel injected cars can see the alt because they have a sensor that looks for it, usually the map and they have an O2. It will adjust the fuel out so the ratio is correct, power still goes down but not as much.
It's also important to remember where blowers and turbos came from, aircrafts that were trying to gain more altitude. They couldn't climb any higher because they didn't have the power. With the forced induction they could get higher than their enemies. That's where nitrous came from too. </TD></TR></TABLE>
Yes, I agree with this, I was just trying to get second opinions to incredteg3's theory (or fact, I dunno) that a turbo is'nt affected at altitude because the wastegate always opens when it sees a preset boost level.
01-18-2005, 09:24 PM
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Re: Boost and altitude (Raf)
HERE ARE SOME LINKS FOR ANYONE WHO SEARCHED FOR THIS SUBJECT AND FOUND THIS THREAD
http://www.sportcompactcarweb....abble/
http://www.clubwrx.net/forums/...61581
http://www.sportcompactcarweb....abble/
http://www.clubwrx.net/forums/...61581
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