VE tune question
07-23-2015 | 09:58 AM
#11
Thread Starter
Joined: Oct 2003
Posts: 11,857
Likes: 438
From: MAHT-O-MEDI
Ok, makes a lot more sense now.
So on a side note, is one bar or about 15psi twice atmospheric pressure? What is essentially double the amount of air of atmosphere?
I know my scuba pressures for depth, but nothing about measurements above sea level.
07-23-2015 | 05:03 PM
#12
Joined: Apr 2003
Posts: 3,243
Likes: 2
From: Northern KY
Originally Posted by Habitforming' timestamp='1437665736' post='23690309
load = manifold pressure
Ok, makes a lot more sense now.
So on a side note, is one bar or about 15psi twice atmospheric pressure? What is essentially double the amount of air of atmosphere?
I know my scuba pressures for depth, but nothing about measurements above sea level.
07-24-2015 | 06:46 AM
#13
Joined: Nov 2007
Posts: 1,384
Likes: 3
Points taken.
Can someone give me a basic understanding on what the load factor is representing as it gets farther from vaccuum? Is it throttle? Is it boost? is it a combination?
In a roots kit throttle and boost should be tied together maybe a little more than others because you can get close to full boost at all rpm. A novi might only get to full boost at 9000 rpm, where I can induce full boost at low rpms but only if I am WOT. Part throttle gets part boost.
At say 4000 rpm, I can have 0 boost, 2 psi, or a full 6 psi depending on how far down my foot is.
Can someone give me a basic understanding on what the load factor is representing as it gets farther from vaccuum? Is it throttle? Is it boost? is it a combination?
In a roots kit throttle and boost should be tied together maybe a little more than others because you can get close to full boost at all rpm. A novi might only get to full boost at 9000 rpm, where I can induce full boost at low rpms but only if I am WOT. Part throttle gets part boost.
At say 4000 rpm, I can have 0 boost, 2 psi, or a full 6 psi depending on how far down my foot is.
07-27-2015 | 11:06 PM
#14
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Joined: Feb 2004
Posts: 591
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From: Lafayette, LA
CID (displacement) x VE x RPM / 2 = Volumetric air flow rate (ACFM)
ACFM x MAP x 520 / IAT = Corrected air flow rate (SCFM)
SCFM x STD air density (lb / cu in) = Mass air flow rate (lb/min)
Mass air flow rate / AF ratio = Mass fuel flow rate (lb/min)
Mass fuel flow rate / single injector rate / # injectors = injector pulse width (the value stored in the lookup table cells).
Displacement is the only constant in these equations. All the rest are changing variables. RPM, MAP & IAT are independent variables (change in their values can't be correlated to another variable). VE, AF ratio, and BSFC are each functions of RPM (change with RPM).
Our OEM, and most other ECU's are speed-density type. They use the 3 independent variable RPM (speed) plus MAP and IAT (air density) to calculate air flow by using the first 3 equations above. VE, AF ratio, and BSFC curves are invisible even to tuner, because they are just one hidden portion of the injector pulse width value that the tuner enters when he gets to proper AF ratio (as measured by UEGO).
TPS is not really needed under steady state conditions. It's mainly used to "trim" or adjust this calc during transients. Like how an accelerator pump on a carb artificially richens the mixture when you stomp on the gas pedal. The sudden increase in air would otherwise cause a lean stumble, until the fuel flow can catch up with the air flow. TPS is also used during very low load conditions, like idle, to help determine when to switch into closed loop mode. During closed loop operation, the EGO is used to further "trim" the injector duty cycle to keep near stoichiometric AF ratio. The TPS is also used as a main axis for the ignition advance lookup table. These TPS functions lead to a significant twist in the ECU (as described below).
Since moset ECU's only use a 3D lookup table, and to keep the axes on the fuel and igniton tables consistent, the 3 axes of both tables are RPM, MAP, and TPS. Even though RPM, MAP, and IAT are the three independent variables. They chose to use TPS instead of IAT as the third axis on the tables. So IAT becomes a separate correction curve which externally adjusts the numbers in the lookup tables.
The VE model ECU's don't need a tuner to manually adjust injector duty cycle until AF ratio is right, then store that value in the cell that corresponds to current operating conditions. The value stored in the lookup table cells is instead AF ratio. So its basically always running in closed loop. You just fill in the "closed loop" curves for VE vs RPM and desired AAF ratio (EGO) vs RPM to get it close.
Some applications, like ITB's, are hard to get a reliable and accurate MAP signal. In that case the tuner must rely more on TPS. They may have a pretty flat MAP correction curve, if still 3D. Or if they go to a 2D table, its main axes are RPM and TPS. That is called n-alpha, instead of speed-density control.
ACFM x MAP x 520 / IAT = Corrected air flow rate (SCFM)
SCFM x STD air density (lb / cu in) = Mass air flow rate (lb/min)
Mass air flow rate / AF ratio = Mass fuel flow rate (lb/min)
Mass fuel flow rate / single injector rate / # injectors = injector pulse width (the value stored in the lookup table cells).
Displacement is the only constant in these equations. All the rest are changing variables. RPM, MAP & IAT are independent variables (change in their values can't be correlated to another variable). VE, AF ratio, and BSFC are each functions of RPM (change with RPM).
Our OEM, and most other ECU's are speed-density type. They use the 3 independent variable RPM (speed) plus MAP and IAT (air density) to calculate air flow by using the first 3 equations above. VE, AF ratio, and BSFC curves are invisible even to tuner, because they are just one hidden portion of the injector pulse width value that the tuner enters when he gets to proper AF ratio (as measured by UEGO).
TPS is not really needed under steady state conditions. It's mainly used to "trim" or adjust this calc during transients. Like how an accelerator pump on a carb artificially richens the mixture when you stomp on the gas pedal. The sudden increase in air would otherwise cause a lean stumble, until the fuel flow can catch up with the air flow. TPS is also used during very low load conditions, like idle, to help determine when to switch into closed loop mode. During closed loop operation, the EGO is used to further "trim" the injector duty cycle to keep near stoichiometric AF ratio. The TPS is also used as a main axis for the ignition advance lookup table. These TPS functions lead to a significant twist in the ECU (as described below).
Since moset ECU's only use a 3D lookup table, and to keep the axes on the fuel and igniton tables consistent, the 3 axes of both tables are RPM, MAP, and TPS. Even though RPM, MAP, and IAT are the three independent variables. They chose to use TPS instead of IAT as the third axis on the tables. So IAT becomes a separate correction curve which externally adjusts the numbers in the lookup tables.
The VE model ECU's don't need a tuner to manually adjust injector duty cycle until AF ratio is right, then store that value in the cell that corresponds to current operating conditions. The value stored in the lookup table cells is instead AF ratio. So its basically always running in closed loop. You just fill in the "closed loop" curves for VE vs RPM and desired AAF ratio (EGO) vs RPM to get it close.
Some applications, like ITB's, are hard to get a reliable and accurate MAP signal. In that case the tuner must rely more on TPS. They may have a pretty flat MAP correction curve, if still 3D. Or if they go to a 2D table, its main axes are RPM and TPS. That is called n-alpha, instead of speed-density control.
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