Dyno Runs / Correction Factors
10-30-2009, 05:02 PM
#61
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volumetric efficiency is altitude independent as long as the total or absolute pressure remains the same...the only difference being at higher altitude Q must increase to maintain the same P due to lower air density, so pumping/friction losses will be marginally greater...but not significant...
10-30-2009, 06:18 PM
#62
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I'm done with the topic, enjoy your mis-understanding.
10-31-2009, 10:13 PM
#63
Drifting
Did some Evelyn Wood speed reading on this long post. Sitting at home handing out candy while the wife is out with the kids getting tricked or hopefully treated.
I've got some real world experience in altitude changes and turbo cars. My main residence and business are in Tucson at about 2000'. I have another business in Greer, AZ at 8500'. When the weather is good, I drive my sports cars to Greer. My current 951 has done this trip many times. My TEC reads manifold pressure. When at 2000' and my wastegate opens at 16psi, my turbo may be be turning 100,000rpm. I don't know if this is the actual rpm and don't care. What I do know is that my turbo is spinning faster at 9000' to get the same manifold pressure as it does at 2000'.
Why my cars feel faster in LA at sea level is a mystery. Maybe it's just the great cement on-ramps and the cool morning damp air. It could be the better gas in CA....LOL?
When I'm at 9000' my guage reads 16psi, and my wastegate opens, my turbo might be spinning at 110,000rpm as their is less mass to compress. To get the same flow of air pressure, my turbo has to work harder to get my wastegate to open at it's set limit.
The numbers on the dyno will be similar if you are reading same manifold pressures.
What I've noticed is the difference in lag, hence my reasoning for getting the smallest hotside, best forged wheel, and Garrett dual BB center section with a large coldside for my new turbo to still have a 500+whp 3.0 motor.
For the original poster, dyno's are good tuning devices. The only way to know if your car is faster is lap times, 1/4 mile times (maybe), or using the same dyno with the same settings with the same air temp, humidity, and keep the correction factors the same. If your turbo car is running 16psi at sea level and netting 300whp and netting 255hp in Denver at the same altitude, you should get a larger compressor side on your turbo. It's running out of it's favorable range, and you should get a more efficient coldside to compensate for the hp killing heat generated.
Here is a post from some folks in Colorado:
* Audi computers are the absolute pressure type and ARE ALTITUDE
CORRECTING.... P (atmospheric) + P (boost pressure) = Absolute Pressure
(guage pressure).... So at sea level, a 5ktq shows .9 (or 1.0 depending on
the guage) when engine off which is atmosphere... The computer allows ~.425
bar pressure (max), so a stock turbo motor (lets take an 87 MC motor with a
stock computer) should see 1.425 bar on the guage at sea level
* At 5000 feet the Density of air is 87% of sea level Density.....
Simplisically translating this, on a 100hp N/A motor @ sea level (no other
changes), will make 87hp (= 87% HP efficient) at 5000 ft.... On a turbo
motor this is mathed differently. First, the NON ALTITUDE compensating
method. Assuming your guage to read 1.0 bar at sea level, it will now read
.845 at 5000 ft. Add in the boost pressure .425bar you get (.845 + .425 =
1.270guage).... Taking this further, lets assume that the turbo motor is
putting out 100hp @ 1.425bar @ sea level..... Go to 5000 ft and you get
1.270 bar absolute of boost, so on a turbo motor (non altitude compensating),
you will be making 89.12hp (89.12% HP efficient) at the same altitude as the
N/A making 87hp.....
* The audi computer has altitude correction built in, so at 5000 ft, the
boost is increased from .425 to .575 (yo, that's audi-eeez, so +/- .0250 is
allowed, took mean for all calculations)... So, with the guage reading .845,
add the .575 = 1.42 absolute... Translating this, the MC motor will be
99.64% HP efficient (and given the altitude pressure table variance of +/-
.0250 of mean, 100% is within spec) of sea level HP @ 5000ft.... All other
things be equal (caveat), there should be NO DIFFERENCE IN POWER LEVELS
BETWEEN YOUR CAR IN CO OR AT SEA LEVEL
* The rule of thumb for turbine speed: +1% for every 5000ft above sea
level.....
* The audi K26 in stock trim spins @ ~100,000 rpm @ 5krpm @ sea level @
1.9bar
* Above 2.0 bar, the efficiency of the turbo DECREASES, as does the cooling
efficiency of the IC
* At 6200rpm the the turbo is spinning ~105,000rpm yet the efficiency of
it's output is reduced by ~3%.... The definition I suppose, of spinning
your wheel without going anywhere....
I've got some real world experience in altitude changes and turbo cars. My main residence and business are in Tucson at about 2000'. I have another business in Greer, AZ at 8500'. When the weather is good, I drive my sports cars to Greer. My current 951 has done this trip many times. My TEC reads manifold pressure. When at 2000' and my wastegate opens at 16psi, my turbo may be be turning 100,000rpm. I don't know if this is the actual rpm and don't care. What I do know is that my turbo is spinning faster at 9000' to get the same manifold pressure as it does at 2000'.
Why my cars feel faster in LA at sea level is a mystery. Maybe it's just the great cement on-ramps and the cool morning damp air. It could be the better gas in CA....LOL?
When I'm at 9000' my guage reads 16psi, and my wastegate opens, my turbo might be spinning at 110,000rpm as their is less mass to compress. To get the same flow of air pressure, my turbo has to work harder to get my wastegate to open at it's set limit.
The numbers on the dyno will be similar if you are reading same manifold pressures.
What I've noticed is the difference in lag, hence my reasoning for getting the smallest hotside, best forged wheel, and Garrett dual BB center section with a large coldside for my new turbo to still have a 500+whp 3.0 motor.
For the original poster, dyno's are good tuning devices. The only way to know if your car is faster is lap times, 1/4 mile times (maybe), or using the same dyno with the same settings with the same air temp, humidity, and keep the correction factors the same. If your turbo car is running 16psi at sea level and netting 300whp and netting 255hp in Denver at the same altitude, you should get a larger compressor side on your turbo. It's running out of it's favorable range, and you should get a more efficient coldside to compensate for the hp killing heat generated.
Here is a post from some folks in Colorado:
* Audi computers are the absolute pressure type and ARE ALTITUDE
CORRECTING.... P (atmospheric) + P (boost pressure) = Absolute Pressure
(guage pressure).... So at sea level, a 5ktq shows .9 (or 1.0 depending on
the guage) when engine off which is atmosphere... The computer allows ~.425
bar pressure (max), so a stock turbo motor (lets take an 87 MC motor with a
stock computer) should see 1.425 bar on the guage at sea level
* At 5000 feet the Density of air is 87% of sea level Density.....
Simplisically translating this, on a 100hp N/A motor @ sea level (no other
changes), will make 87hp (= 87% HP efficient) at 5000 ft.... On a turbo
motor this is mathed differently. First, the NON ALTITUDE compensating
method. Assuming your guage to read 1.0 bar at sea level, it will now read
.845 at 5000 ft. Add in the boost pressure .425bar you get (.845 + .425 =
1.270guage).... Taking this further, lets assume that the turbo motor is
putting out 100hp @ 1.425bar @ sea level..... Go to 5000 ft and you get
1.270 bar absolute of boost, so on a turbo motor (non altitude compensating),
you will be making 89.12hp (89.12% HP efficient) at the same altitude as the
N/A making 87hp.....
* The audi computer has altitude correction built in, so at 5000 ft, the
boost is increased from .425 to .575 (yo, that's audi-eeez, so +/- .0250 is
allowed, took mean for all calculations)... So, with the guage reading .845,
add the .575 = 1.42 absolute... Translating this, the MC motor will be
99.64% HP efficient (and given the altitude pressure table variance of +/-
.0250 of mean, 100% is within spec) of sea level HP @ 5000ft.... All other
things be equal (caveat), there should be NO DIFFERENCE IN POWER LEVELS
BETWEEN YOUR CAR IN CO OR AT SEA LEVEL
* The rule of thumb for turbine speed: +1% for every 5000ft above sea
level.....
* The audi K26 in stock trim spins @ ~100,000 rpm @ 5krpm @ sea level @
1.9bar
* Above 2.0 bar, the efficiency of the turbo DECREASES, as does the cooling
efficiency of the IC
* At 6200rpm the the turbo is spinning ~105,000rpm yet the efficiency of
it's output is reduced by ~3%.... The definition I suppose, of spinning
your wheel without going anywhere....
11-01-2009, 12:10 AM
#64
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Did some Evelyn Wood speed reading on this long post. Sitting at home handing out candy while the wife is out with the kids getting tricked or hopefully treated.
I've got some real world experience in altitude changes and turbo cars. My main residence and business are in Tucson at about 2000'. I have another business in Greer, AZ at 8500'. When the weather is good, I drive my sports cars to Greer. My current 951 has done this trip many times. My TEC reads manifold pressure. When at 2000' and my wastegate opens at 16psi, my turbo may be be turning 100,000rpm. I don't know if this is the actual rpm and don't care. What I do know is that my turbo is spinning faster at 9000' to get the same manifold pressure as it does at 2000'.
Why my cars feel faster in LA at sea level is a mystery. Maybe it's just the great cement on-ramps and the cool morning damp air. It could be the better gas in CA....LOL?
When I'm at 9000' my guage reads 16psi, and my wastegate opens, my turbo might be spinning at 110,000rpm as their is less mass to compress. To get the same flow of air pressure, my turbo has to work harder to get my wastegate to open at it's set limit.
The numbers on the dyno will be similar if you are reading same manifold pressures.
What I've noticed is the difference in lag, hence my reasoning for getting the smallest hotside, best forged wheel, and Garrett dual BB center section with a large coldside for my new turbo to still have a 500+whp 3.0 motor.
For the original poster, dyno's are good tuning devices. The only way to know if your car is faster is lap times, 1/4 mile times (maybe), or using the same dyno with the same settings with the same air temp, humidity, and keep the correction factors the same. If your turbo car is running 16psi at sea level and netting 300whp and netting 255hp in Denver at the same altitude, you should get a larger compressor side on your turbo. It's running out of it's favorable range, and you should get a more efficient coldside to compensate for the hp killing heat generated.
Here is a post from some folks in Colorado:
* Audi computers are the absolute pressure type and ARE ALTITUDE
CORRECTING.... P (atmospheric) + P (boost pressure) = Absolute Pressure
(guage pressure).... So at sea level, a 5ktq shows .9 (or 1.0 depending on
the guage) when engine off which is atmosphere... The computer allows ~.425
bar pressure (max), so a stock turbo motor (lets take an 87 MC motor with a
stock computer) should see 1.425 bar on the guage at sea level
* At 5000 feet the Density of air is 87% of sea level Density.....
Simplisically translating this, on a 100hp N/A motor @ sea level (no other
changes), will make 87hp (= 87% HP efficient) at 5000 ft.... On a turbo
motor this is mathed differently. First, the NON ALTITUDE compensating
method. Assuming your guage to read 1.0 bar at sea level, it will now read
.845 at 5000 ft. Add in the boost pressure .425bar you get (.845 + .425 =
1.270guage).... Taking this further, lets assume that the turbo motor is
putting out 100hp @ 1.425bar @ sea level..... Go to 5000 ft and you get
1.270 bar absolute of boost, so on a turbo motor (non altitude compensating),
you will be making 89.12hp (89.12% HP efficient) at the same altitude as the
N/A making 87hp.....
* The audi computer has altitude correction built in, so at 5000 ft, the
boost is increased from .425 to .575 (yo, that's audi-eeez, so +/- .0250 is
allowed, took mean for all calculations)... So, with the guage reading .845,
add the .575 = 1.42 absolute... Translating this, the MC motor will be
99.64% HP efficient (and given the altitude pressure table variance of +/-
.0250 of mean, 100% is within spec) of sea level HP @ 5000ft.... All other
things be equal (caveat), there should be NO DIFFERENCE IN POWER LEVELS
BETWEEN YOUR CAR IN CO OR AT SEA LEVEL
* The rule of thumb for turbine speed: +1% for every 5000ft above sea
level.....
* The audi K26 in stock trim spins @ ~100,000 rpm @ 5krpm @ sea level @
1.9bar
* Above 2.0 bar, the efficiency of the turbo DECREASES, as does the cooling
efficiency of the IC
* At 6200rpm the the turbo is spinning ~105,000rpm yet the efficiency of
it's output is reduced by ~3%.... The definition I suppose, of spinning
your wheel without going anywhere....
I've got some real world experience in altitude changes and turbo cars. My main residence and business are in Tucson at about 2000'. I have another business in Greer, AZ at 8500'. When the weather is good, I drive my sports cars to Greer. My current 951 has done this trip many times. My TEC reads manifold pressure. When at 2000' and my wastegate opens at 16psi, my turbo may be be turning 100,000rpm. I don't know if this is the actual rpm and don't care. What I do know is that my turbo is spinning faster at 9000' to get the same manifold pressure as it does at 2000'.
Why my cars feel faster in LA at sea level is a mystery. Maybe it's just the great cement on-ramps and the cool morning damp air. It could be the better gas in CA....LOL?
When I'm at 9000' my guage reads 16psi, and my wastegate opens, my turbo might be spinning at 110,000rpm as their is less mass to compress. To get the same flow of air pressure, my turbo has to work harder to get my wastegate to open at it's set limit.
The numbers on the dyno will be similar if you are reading same manifold pressures.
What I've noticed is the difference in lag, hence my reasoning for getting the smallest hotside, best forged wheel, and Garrett dual BB center section with a large coldside for my new turbo to still have a 500+whp 3.0 motor.
For the original poster, dyno's are good tuning devices. The only way to know if your car is faster is lap times, 1/4 mile times (maybe), or using the same dyno with the same settings with the same air temp, humidity, and keep the correction factors the same. If your turbo car is running 16psi at sea level and netting 300whp and netting 255hp in Denver at the same altitude, you should get a larger compressor side on your turbo. It's running out of it's favorable range, and you should get a more efficient coldside to compensate for the hp killing heat generated.
Here is a post from some folks in Colorado:
* Audi computers are the absolute pressure type and ARE ALTITUDE
CORRECTING.... P (atmospheric) + P (boost pressure) = Absolute Pressure
(guage pressure).... So at sea level, a 5ktq shows .9 (or 1.0 depending on
the guage) when engine off which is atmosphere... The computer allows ~.425
bar pressure (max), so a stock turbo motor (lets take an 87 MC motor with a
stock computer) should see 1.425 bar on the guage at sea level
* At 5000 feet the Density of air is 87% of sea level Density.....
Simplisically translating this, on a 100hp N/A motor @ sea level (no other
changes), will make 87hp (= 87% HP efficient) at 5000 ft.... On a turbo
motor this is mathed differently. First, the NON ALTITUDE compensating
method. Assuming your guage to read 1.0 bar at sea level, it will now read
.845 at 5000 ft. Add in the boost pressure .425bar you get (.845 + .425 =
1.270guage).... Taking this further, lets assume that the turbo motor is
putting out 100hp @ 1.425bar @ sea level..... Go to 5000 ft and you get
1.270 bar absolute of boost, so on a turbo motor (non altitude compensating),
you will be making 89.12hp (89.12% HP efficient) at the same altitude as the
N/A making 87hp.....
* The audi computer has altitude correction built in, so at 5000 ft, the
boost is increased from .425 to .575 (yo, that's audi-eeez, so +/- .0250 is
allowed, took mean for all calculations)... So, with the guage reading .845,
add the .575 = 1.42 absolute... Translating this, the MC motor will be
99.64% HP efficient (and given the altitude pressure table variance of +/-
.0250 of mean, 100% is within spec) of sea level HP @ 5000ft.... All other
things be equal (caveat), there should be NO DIFFERENCE IN POWER LEVELS
BETWEEN YOUR CAR IN CO OR AT SEA LEVEL
* The rule of thumb for turbine speed: +1% for every 5000ft above sea
level.....
* The audi K26 in stock trim spins @ ~100,000 rpm @ 5krpm @ sea level @
1.9bar
* Above 2.0 bar, the efficiency of the turbo DECREASES, as does the cooling
efficiency of the IC
* At 6200rpm the the turbo is spinning ~105,000rpm yet the efficiency of
it's output is reduced by ~3%.... The definition I suppose, of spinning
your wheel without going anywhere....
That is why with a MBC, you have to increase boost to get the same absolute manifold pressure.
-
Dana
11-01-2009, 12:32 AM
#65
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Here is why this is a difference.
http://www.autoshop101.com/forms/h35.pdf
MAP sensors use read abosoluet pressure because they are referenced to the "perfect" (or very good) vacuum in the silicone sensor.
A typical boost gauge reads gauge pressure because of being referenced to the vacuum as the MAP sensor is, it is referenced to the atmosphere (I should take it out of my car but I bet there is a vent hole in the gauge as a reference).
So, for us guys in CO where altitude can change (its not hard to get 1000ft change) it seems the best solution is controlling the wastegate electronically via an electronic boost controllerthat uses a MAP.
This may be the solution...???
-Dana
http://www.autoshop101.com/forms/h35.pdf
MAP sensors use read abosoluet pressure because they are referenced to the "perfect" (or very good) vacuum in the silicone sensor.
A typical boost gauge reads gauge pressure because of being referenced to the vacuum as the MAP sensor is, it is referenced to the atmosphere (I should take it out of my car but I bet there is a vent hole in the gauge as a reference).
So, for us guys in CO where altitude can change (its not hard to get 1000ft change) it seems the best solution is controlling the wastegate electronically via an electronic boost controllerthat uses a MAP.
This may be the solution...???
-Dana
11-01-2009, 12:56 AM
#66
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Dana: What shop did you do the dyno run on? I've got a K27/6 with Vitesse MAF that I've been wanting to get some numbers on, it would be interesting to do it at the same shop.
11-01-2009, 01:59 AM
#67
Drifting
Please read:
What exactly is meant by Manifold Pressure?
The manifold pressure gauge is an engine instrument typically used in piston engines to measure the pressure inside the induction system of an engine. In other words, it literally reads the pressure inside the induction system.
Correction: A good driver is always learning right? Well, since writing this post I have learned that the manifold pressure gauge is really NOT about pressure but about suction! Think about it. Your whole engine (especially the cylinders) is a big vacuum pump. Every time the piston drops into the “intake” stroke it is literally pulling or sucking air into the cylinder. Your manifold pressure gauge is actually reading suction not ram air pressure. That’s why at idle power your manifold pressure gauge might read 10 or 12 inches when the outside ambient pressure is 30 inches. Your engine is literally starving for air! It is creating a vacuum or negative pressure inside the intake manifold.
The induction system of couse being the air / fuel mixture that is between the throttle and the cylinders.
This measurement, which is read in inches of mercury or “in hg”, is one of the best methods to determine just how much power is being developed by the engine. The more air and fuel we can pump or pull into the cylinders, the more power the engine can develop. When you can measure how much air pressure is in the induction system, just before the air / fuel mixture enters into the cylinders, you will have a good idea of how much power you are developing.
In normally aspirated engines (non turbo-charged), the manifold pressure gauge has a range of anwhere between 10 – 40 in. hg (or inches of mercury). In a turbocharged engine, the manifold pressure is allowed to go as high as the engine manufacturer, or builder specs allows. When the engine is shut down, the manifold pressure gauge should read very close to the current atmospheric pressure setting.
Men, measurement of boost at the manifold is what it is. What is your point here? Elevation has no merit and doesn't require anything but better intercooling or a larger colde side of the turbo with more lag to get similar results as sea level.
We can make the same HP and TQ levels at altitude with better inter-cooling and a larger compressor. Lag is the result, but that's just the deal. Hey the skiing is much better up high. Lag is not that big of a deal if you are willing to get the right turbo.
G
What exactly is meant by Manifold Pressure?
The manifold pressure gauge is an engine instrument typically used in piston engines to measure the pressure inside the induction system of an engine. In other words, it literally reads the pressure inside the induction system.
Correction: A good driver is always learning right? Well, since writing this post I have learned that the manifold pressure gauge is really NOT about pressure but about suction! Think about it. Your whole engine (especially the cylinders) is a big vacuum pump. Every time the piston drops into the “intake” stroke it is literally pulling or sucking air into the cylinder. Your manifold pressure gauge is actually reading suction not ram air pressure. That’s why at idle power your manifold pressure gauge might read 10 or 12 inches when the outside ambient pressure is 30 inches. Your engine is literally starving for air! It is creating a vacuum or negative pressure inside the intake manifold.
The induction system of couse being the air / fuel mixture that is between the throttle and the cylinders.
This measurement, which is read in inches of mercury or “in hg”, is one of the best methods to determine just how much power is being developed by the engine. The more air and fuel we can pump or pull into the cylinders, the more power the engine can develop. When you can measure how much air pressure is in the induction system, just before the air / fuel mixture enters into the cylinders, you will have a good idea of how much power you are developing.
In normally aspirated engines (non turbo-charged), the manifold pressure gauge has a range of anwhere between 10 – 40 in. hg (or inches of mercury). In a turbocharged engine, the manifold pressure is allowed to go as high as the engine manufacturer, or builder specs allows. When the engine is shut down, the manifold pressure gauge should read very close to the current atmospheric pressure setting.
Men, measurement of boost at the manifold is what it is. What is your point here? Elevation has no merit and doesn't require anything but better intercooling or a larger colde side of the turbo with more lag to get similar results as sea level.
We can make the same HP and TQ levels at altitude with better inter-cooling and a larger compressor. Lag is the result, but that's just the deal. Hey the skiing is much better up high. Lag is not that big of a deal if you are willing to get the right turbo.
G
11-01-2009, 09:53 AM
#68
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http://theboostcreepltd.com/
They are at highway 66 and I-25.
New shop. Really nice guys. They are really new (4 weeks).
-Dana
11-01-2009, 10:04 AM
#69
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Please read:
What exactly is meant by Manifold Pressure?
The manifold pressure gauge is an engine instrument typically used in piston engines to measure the pressure inside the induction system of an engine. In other words, it literally reads the pressure inside the induction system.
Correction: A good driver is always learning right? Well, since writing this post I have learned that the manifold pressure gauge is really NOT about pressure but about suction! Think about it. Your whole engine (especially the cylinders) is a big vacuum pump. Every time the piston drops into the “intake” stroke it is literally pulling or sucking air into the cylinder. Your manifold pressure gauge is actually reading suction not ram air pressure. That’s why at idle power your manifold pressure gauge might read 10 or 12 inches when the outside ambient pressure is 30 inches. Your engine is literally starving for air! It is creating a vacuum or negative pressure inside the intake manifold.
The induction system of couse being the air / fuel mixture that is between the throttle and the cylinders.
This measurement, which is read in inches of mercury or “in hg”, is one of the best methods to determine just how much power is being developed by the engine. The more air and fuel we can pump or pull into the cylinders, the more power the engine can develop. When you can measure how much air pressure is in the induction system, just before the air / fuel mixture enters into the cylinders, you will have a good idea of how much power you are developing.
In normally aspirated engines (non turbo-charged), the manifold pressure gauge has a range of anwhere between 10 – 40 in. hg (or inches of mercury). In a turbocharged engine, the manifold pressure is allowed to go as high as the engine manufacturer, or builder specs allows. When the engine is shut down, the manifold pressure gauge should read very close to the current atmospheric pressure setting.
Men, measurement of boost at the manifold is what it is. What is your point here? Elevation has no merit and doesn't require anything but better intercooling or a larger colde side of the turbo with more lag to get similar results as sea level.
We can make the same HP and TQ levels at altitude with better inter-cooling and a larger compressor. Lag is the result, but that's just the deal. Hey the skiing is much better up high. Lag is not that big of a deal if you are willing to get the right turbo.
G
What exactly is meant by Manifold Pressure?
The manifold pressure gauge is an engine instrument typically used in piston engines to measure the pressure inside the induction system of an engine. In other words, it literally reads the pressure inside the induction system.
Correction: A good driver is always learning right? Well, since writing this post I have learned that the manifold pressure gauge is really NOT about pressure but about suction! Think about it. Your whole engine (especially the cylinders) is a big vacuum pump. Every time the piston drops into the “intake” stroke it is literally pulling or sucking air into the cylinder. Your manifold pressure gauge is actually reading suction not ram air pressure. That’s why at idle power your manifold pressure gauge might read 10 or 12 inches when the outside ambient pressure is 30 inches. Your engine is literally starving for air! It is creating a vacuum or negative pressure inside the intake manifold.
The induction system of couse being the air / fuel mixture that is between the throttle and the cylinders.
This measurement, which is read in inches of mercury or “in hg”, is one of the best methods to determine just how much power is being developed by the engine. The more air and fuel we can pump or pull into the cylinders, the more power the engine can develop. When you can measure how much air pressure is in the induction system, just before the air / fuel mixture enters into the cylinders, you will have a good idea of how much power you are developing.
In normally aspirated engines (non turbo-charged), the manifold pressure gauge has a range of anwhere between 10 – 40 in. hg (or inches of mercury). In a turbocharged engine, the manifold pressure is allowed to go as high as the engine manufacturer, or builder specs allows. When the engine is shut down, the manifold pressure gauge should read very close to the current atmospheric pressure setting.
Men, measurement of boost at the manifold is what it is. What is your point here? Elevation has no merit and doesn't require anything but better intercooling or a larger colde side of the turbo with more lag to get similar results as sea level.
We can make the same HP and TQ levels at altitude with better inter-cooling and a larger compressor. Lag is the result, but that's just the deal. Hey the skiing is much better up high. Lag is not that big of a deal if you are willing to get the right turbo.
G
Yes, the pressure inside the manifold is what it is, but what we are talking about is what value (psia or psig) is measured. The two values differ a few psi depending upon the altitude.
Also, a manual boost controller is two springs and a ball. I know you only see one spring, the but the other "spring" is the air on the back side side of the ball. So you have a spring + atmospheric pressure on one side of the ball and "boost pressure" on the other side. When boost pressure overcomes the spring + airpressure, it opens the wastegate (with a little more complication than that because the wastegate is also differential with a spring + atmospheric pressure on one side and boost on the other)
The other general question, that I have not figured out in my head is fueling. Are chips set for psia or psig? The issue with chip mapping is that if you are running 2 or 3psi more pressure than the fuel map is expecting, a lean condition can occur. Thats normally not good.
Yes, we can make the "sam"e power with bigger turbos and better intercooler but then its not making the same power with the same parts. That is what the whole correction factor discussion is about.
-Dana
11-01-2009, 07:17 PM
#70
Rennlist Member
The other general question, that I have not figured out in my head is fueling. Are chips set for psia or psig? The issue with chip mapping is that if you are running 2 or 3psi more pressure than the fuel map is expecting, a lean condition can occur. Thats normally not good.
-Dana
-Dana
The chips are basically set for psia.
Or, better said, the air flow sensor gives the right information to the computer. A MAF will sense the right airflow whether it's at sea level, or is higher up and the turbo is pushing more boost to compensate for the thinner air. Even the stock barn door opens according to the pressure differential between the front and the back of the flapper.
