2 Bar Question
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From: http://www.mphparts.com 800-364-1975
I think you need a 2 bar setup if you're going to run any boost at all and want your PCM to directly account for it. Aren't our cars setup for 1 bar right now (various vacuum ranges all the way up to atmospheric pressure or 0 psi)?
*edit: If you're going to run any boost and want your MAP tables to account for it. Clearly you can run boost on a MAF only or MAF + 1 bar MAP application.
*edit: If you're going to run any boost and want your MAP tables to account for it. Clearly you can run boost on a MAF only or MAF + 1 bar MAP application.
Last edited by Tony @ MPH; May 17, 2005 at 06:40 PM.
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Joined: Mar 2002
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From: Tx
Here is the deal, our PCMs are very advanced and in normal operation (often referred to as MAF mode) use a combination of airflow estimation inputs to perform the fueling calculations. The two inputs are based on two different airflow sensors (MAF and MAP). The MAF sensor uses a simple transfer function where x frequency = x airflow. The MAP sensor uses a more complex calculation based on a 2 dimensional table (often called the VE table) that includes MAP and RPM. It also uses IAT in this calculation to come up with an estimated airflow. If you have good scanner you can read the maf value in g/sec as a PID called GM.MAF and you can read the calculated MAP airflow in g/sec as a PID called GM.DYNAIR.
In MAF mode it uses a very complex state machine to determine how to utilize the two different airflow values, but you can generically say that the MAP sensor is ignored once you go beyond 4k RPMs. It is really only used below 4k rpms for throttle transitions (non steady states). This is mainly because the MAF sensor is located outside the intake and it can’t see things accurately under some conditions (like when the TB first opens).
This MAF mode actually works fairly well on a boosted car (up to a certain point) because the MAF tends to be the heavyweight in all the calculations and the MAF tends to be pretty accurate. The problem comes in when you start pushing more air then the MAF can read. This is not boost dependent, but is specifically airflow dependent. So a car making 20psi at 3k rpms would not be maxing the MAF, but that same car making 10psi at 6k rpms would definitely be outside the internal MAF limit (which is 512g/sec no matter how the maf is calibrated). There is one trick that can be played to get around this 512g/sec MAF limitation, but I will describe that later.
So, most boosted cars making good power do max the MAF, but there is a simple way to tune that is fairly independent of airflow. It is called power enrichment and it is a PCM calibration table that provides a mechanism to adjust the target AF ratio based on RPM. This is how all boosted cars (running MAF mode) are tuned once the maf is out of range. It works pretty good on supercharged setups, since boost and airflow are pretty much tied to RPM in the first place. It is a bit less useful on turbo setups, since boost and RPM can be completely independent. In general though, boost follows a pretty consistent pattern above 4k rpms (unless you are making heavy use of a boost controller). There is also a lack of accuracy on supercharged cars, since they tend to make differing amounts of boost depending on the density of the intake air. In short, PE tuning works fairly well since boost is farily consistent at high RPMS.
That is how MAF mode works and it is good enough for most cars (in the 5-600RWHP range). The tune is not perfect and adaptive in the high power areas, but it is generally good enough if you keep the tune safe and don’t get too greedy.
SD mode is similar to MAF mode except that you only have one input for the Airflow calculation and that is the MAP sensor and the VE table (DYNAIR). The stock MAP sensor only goes up to 105kpa (atmospheric), so running SD with a stock MAP sensor on a boosted car is almost impossible (you will see that as soon as you open the TB). Running a 2bar map sensor allows you to tune the VE table up to about 15psi. This is great, but the process of actually doing the tuning is very painful and time consuming. You really need a load bearing dyno where you can put the car in each cell of the VE table (MAPxRPM) and determine what the airflow/fueling requirement is. This could take quite a bit of time and a mistake could mean a lean spot and a melt down. I really doubt that most tuners would spend the time to really do the SD tune 100% correctly. If they did, they should charge you a good chunk of change. Most will just hit a few cells in then using smoothing to fill in the blanks. SD tuning (unlike MAF mode) is very unforgiving.
Back to the MAF trick, you can actually trick the PCM internally and get around the 512 g/sec limit by splitting things in half. In other words, make the PCM think your injectors are half as big as they really are and make it think that 512g/sec of air is only 256… This works, but you need a MAF that can read some major air with a solid calibration from a good flow bench.
I hope all that makes some sense and clears a few things up. I think you could do fine with a MAF tune at 10psi.
In MAF mode it uses a very complex state machine to determine how to utilize the two different airflow values, but you can generically say that the MAP sensor is ignored once you go beyond 4k RPMs. It is really only used below 4k rpms for throttle transitions (non steady states). This is mainly because the MAF sensor is located outside the intake and it can’t see things accurately under some conditions (like when the TB first opens).
This MAF mode actually works fairly well on a boosted car (up to a certain point) because the MAF tends to be the heavyweight in all the calculations and the MAF tends to be pretty accurate. The problem comes in when you start pushing more air then the MAF can read. This is not boost dependent, but is specifically airflow dependent. So a car making 20psi at 3k rpms would not be maxing the MAF, but that same car making 10psi at 6k rpms would definitely be outside the internal MAF limit (which is 512g/sec no matter how the maf is calibrated). There is one trick that can be played to get around this 512g/sec MAF limitation, but I will describe that later.
So, most boosted cars making good power do max the MAF, but there is a simple way to tune that is fairly independent of airflow. It is called power enrichment and it is a PCM calibration table that provides a mechanism to adjust the target AF ratio based on RPM. This is how all boosted cars (running MAF mode) are tuned once the maf is out of range. It works pretty good on supercharged setups, since boost and airflow are pretty much tied to RPM in the first place. It is a bit less useful on turbo setups, since boost and RPM can be completely independent. In general though, boost follows a pretty consistent pattern above 4k rpms (unless you are making heavy use of a boost controller). There is also a lack of accuracy on supercharged cars, since they tend to make differing amounts of boost depending on the density of the intake air. In short, PE tuning works fairly well since boost is farily consistent at high RPMS.
That is how MAF mode works and it is good enough for most cars (in the 5-600RWHP range). The tune is not perfect and adaptive in the high power areas, but it is generally good enough if you keep the tune safe and don’t get too greedy.
SD mode is similar to MAF mode except that you only have one input for the Airflow calculation and that is the MAP sensor and the VE table (DYNAIR). The stock MAP sensor only goes up to 105kpa (atmospheric), so running SD with a stock MAP sensor on a boosted car is almost impossible (you will see that as soon as you open the TB). Running a 2bar map sensor allows you to tune the VE table up to about 15psi. This is great, but the process of actually doing the tuning is very painful and time consuming. You really need a load bearing dyno where you can put the car in each cell of the VE table (MAPxRPM) and determine what the airflow/fueling requirement is. This could take quite a bit of time and a mistake could mean a lean spot and a melt down. I really doubt that most tuners would spend the time to really do the SD tune 100% correctly. If they did, they should charge you a good chunk of change. Most will just hit a few cells in then using smoothing to fill in the blanks. SD tuning (unlike MAF mode) is very unforgiving.
Back to the MAF trick, you can actually trick the PCM internally and get around the 512 g/sec limit by splitting things in half. In other words, make the PCM think your injectors are half as big as they really are and make it think that 512g/sec of air is only 256… This works, but you need a MAF that can read some major air with a solid calibration from a good flow bench.
I hope all that makes some sense and clears a few things up. I think you could do fine with a MAF tune at 10psi.
Last edited by QuickSilver2002; May 17, 2005 at 08:32 PM.
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Joined: Apr 2001
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From: Torrance CA
Originally Posted by QuickSilver2002
Here is the deal, our PCMs are very advanced and in normal operation (often referred to as MAF mode) use a combination of airflow estimation inputs to perform the fueling calculations. The two inputs are based on two different airflow sensors (MAF and MAP). The MAF sensor uses a simple transfer function where x frequency = x airflow. The MAP sensor uses a more complex calculation based on a 2 dimensional table (often called the VE table) that includes MAP and RPM. It also uses IAT in this calculation to come up with an estimated airflow. If you have good scanner you can read the maf value in g/sec as a PID called GM.MAF and you can read the calculated MAP airflow in g/sec as a PID called GM.DYNAIR.
In MAF mode it uses a very complex state machine to determine how to utilize the two different airflow values, but you can generically say that the MAP sensor is ignored once you go beyond 4k RPMs. It is really only used below 4k rpms for throttle transitions (non steady states). This is mainly because the MAF sensor is located outside the intake and it can’t see things accurately under some conditions (like when the TB first opens).
This MAF mode actually works fairly well on a boosted car (up to a certain point) because the MAF tends to be the heavyweight in all the calculations and the MAF tends to be pretty accurate. The problem comes in when you start pushing more air then the MAF can read. This is not boost dependent, but is specifically airflow dependent. So a car making 20psi at 3k rpms would not be maxing the MAF, but that same car making 10psi at 6k rpms would definitely be outside the internal MAF limit (which is 512g/sec no matter how the maf is calibrated). There is one trick that can be played to get around this 512g/sec MAF limitation, but I will describe that later.
So, most boosted cars making good power do max the MAF, but there is a simple way to tune that is fairly independent of airflow. It is called power enrichment and it is a PCM calibration table that provides a mechanism to adjust the target AF ratio based on RPM. This is how all boosted cars (running MAF mode) are tuned once the maf is out of range. It works pretty good on supercharged setups, since boost and airflow are pretty much tied to RPM in the first place. It is a bit less useful on turbo setups, since boost and RPM can be completely independent. In general though, boost follows a pretty consistent pattern above 4k rpms (unless you are making heavy use of a boost controller). There is also a lack of accuracy on supercharged cars, since they tend to make differing amounts of boost depending on the density of the intake air. In short, PE tuning works fairly well since boost is farily consistent at high RPMS.
That is how MAF mode works and it is good enough for most cars (in the 5-600RWHP range). The tune is not perfect and adaptive in the high power areas, but it is generally good enough if you keep the tune safe and don’t get too greedy.
SD mode is similar to MAF mode except that you only have one input for the Airflow calculation and that is the MAP sensor and the VE table (DYNAIR). The stock MAP sensor only goes up to 105kpa (atmospheric), so running SD with a stock MAP sensor on a boosted car is almost impossible (you will see that as soon as you open the TB). Running a 2bar map sensor allows you to tune the VE table up to about 15psi. This is great, but the process of actually doing the tuning is very painful and time consuming. You really need a load bearing dyno where you can put the car in each cell of the VE table (MAPxRPM) and determine what the airflow/fueling requirement is. This could take quite a bit of time and a mistake could mean a lean spot and a melt down. I really doubt that most tuners would spend the time to really do the SD tune 100% correctly. If they did, they should charge you a good chunk of change. Most will just hit a few cells in then using smoothing to fill in the blanks. SD tuning (unlike MAF mode) is very unforgiving.
Back to the MAF trick, you can actually trick the PCM internally and get around the 512 g/sec limit by splitting things in half. In other words, make the PCM think your injectors are half as big as they really are and make it think that 512g/sec of air is only 256… This works, but you need a MAF that can read some major air with a solid calibration from a good flow bench.
I hope all that makes some sense and clears a few things up. I think you could do fine with a MAF tune at 10psi.
In MAF mode it uses a very complex state machine to determine how to utilize the two different airflow values, but you can generically say that the MAP sensor is ignored once you go beyond 4k RPMs. It is really only used below 4k rpms for throttle transitions (non steady states). This is mainly because the MAF sensor is located outside the intake and it can’t see things accurately under some conditions (like when the TB first opens).
This MAF mode actually works fairly well on a boosted car (up to a certain point) because the MAF tends to be the heavyweight in all the calculations and the MAF tends to be pretty accurate. The problem comes in when you start pushing more air then the MAF can read. This is not boost dependent, but is specifically airflow dependent. So a car making 20psi at 3k rpms would not be maxing the MAF, but that same car making 10psi at 6k rpms would definitely be outside the internal MAF limit (which is 512g/sec no matter how the maf is calibrated). There is one trick that can be played to get around this 512g/sec MAF limitation, but I will describe that later.
So, most boosted cars making good power do max the MAF, but there is a simple way to tune that is fairly independent of airflow. It is called power enrichment and it is a PCM calibration table that provides a mechanism to adjust the target AF ratio based on RPM. This is how all boosted cars (running MAF mode) are tuned once the maf is out of range. It works pretty good on supercharged setups, since boost and airflow are pretty much tied to RPM in the first place. It is a bit less useful on turbo setups, since boost and RPM can be completely independent. In general though, boost follows a pretty consistent pattern above 4k rpms (unless you are making heavy use of a boost controller). There is also a lack of accuracy on supercharged cars, since they tend to make differing amounts of boost depending on the density of the intake air. In short, PE tuning works fairly well since boost is farily consistent at high RPMS.
That is how MAF mode works and it is good enough for most cars (in the 5-600RWHP range). The tune is not perfect and adaptive in the high power areas, but it is generally good enough if you keep the tune safe and don’t get too greedy.
SD mode is similar to MAF mode except that you only have one input for the Airflow calculation and that is the MAP sensor and the VE table (DYNAIR). The stock MAP sensor only goes up to 105kpa (atmospheric), so running SD with a stock MAP sensor on a boosted car is almost impossible (you will see that as soon as you open the TB). Running a 2bar map sensor allows you to tune the VE table up to about 15psi. This is great, but the process of actually doing the tuning is very painful and time consuming. You really need a load bearing dyno where you can put the car in each cell of the VE table (MAPxRPM) and determine what the airflow/fueling requirement is. This could take quite a bit of time and a mistake could mean a lean spot and a melt down. I really doubt that most tuners would spend the time to really do the SD tune 100% correctly. If they did, they should charge you a good chunk of change. Most will just hit a few cells in then using smoothing to fill in the blanks. SD tuning (unlike MAF mode) is very unforgiving.
Back to the MAF trick, you can actually trick the PCM internally and get around the 512 g/sec limit by splitting things in half. In other words, make the PCM think your injectors are half as big as they really are and make it think that 512g/sec of air is only 256… This works, but you need a MAF that can read some major air with a solid calibration from a good flow bench.
I hope all that makes some sense and clears a few things up. I think you could do fine with a MAF tune at 10psi.
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