soarerflame
12-05-2005, 08:51 PM
This is all thanks to KIP SIPMANN
This on a sentra but the same basic theory applies across the board:
http://www.nissanperformancemag.com/may03/project_qg18de/images/pImgLeft_electronics_safc1.jpg
The S-AFC intercepts the signal from the airflow meter before it gets to the ECU (Engine Control Unit) and adjusts it to trick the ECU into thinking it's getting more or less air in order to increase or decrease the fuel it adds. It gives you direct control over the amount of fuel going into your engine. Of course, you then have the potential to damage your engine if you try and tune it without an air/fuel meter hooked up.
http://www.nissanperformancemag.com/may03/project_qg18de/images/safc00.jpg
If you know your car is running rich or lean at certain rev ranges and throttle positions, then you are not getting the full power potential from your engine. After having our stock intake manifold Extrude Honed, Project QG18DE was running a very unfavorable air/fuel ratio. It was so unsafe we didn't even want to dyno the car for fear of causing major damage to the motor under high RPM. Therefore, the need for an air/fuel controller was evident.
The air/fuel ratio is a very common source of confusion to many people. It is the ratio of air to fuel exiting from the engine and a good measure of engine tune. The air/fuel ratio is commonly represented as a single numeral as in 14.7. This actually represents the number of air particles exiting per single fuel molecule (ie.,14.7:1). The 14.7:1 just mentioned is actually what is called stoichiometric, or the ideal air/fuel ratio at which temperatures are controlled and fuel economy is optimized. The air/fuel ratio affects the heat generated during the combustion phase of the engine cycle. Fuel acts as a cooling agent for the cycle. Having a numerically lower air/fuel ratio (less than stoichiometric) is considered to be a RICH condition (ie., richer in the amount of gas exiting) and will result in lower exhaust gas temperatures (EGTs). Conversely, leaning out the mixture by injecting less gasoline causes the overall exhaust gas temperatures to rise. A change from a lean to a rich mixture can cool the exhaust charge by as much as 400 degrees Fahrenheit. The air/fuel ratio can be monitored by an air/fuel gauge or an exhaust gas temperature gauge. An A/F gauge shows the instantaneous mixture while an EGT gauge shows the actual temperatures in the engine to check its condition.
Some common air/fuel ratio misconceptions:
1) Running an extremely rich air/fuel ratio creates more power:
This is a good one for novices who think that you need to consume every last bit of air going into an engine. Actually an engine spits out most of the air it ingests as the ignition cycle for a particular cylinder is far too small and short to effectively utilize the entire air mixture. When high-powered turbo cars or N/A (naturally aspirated) cars run extremely rich mixtures, it is to keep cylinder temperatures down. Frequently cars gain power as they run more optimized air/fuel ratios, typically slightly richer than stoichiometric. In addition, rich mixtures can wear out sensors, waste gas, and clog your catalytic converter. If it were true that more gas always equaled more power, racecars would simply dump fuel directly into the ports instead of worrying about metering. Tuning is the key!
2) Going lean creates an 'instant detonation' condition:
In the case of street engines, this just isn't true. Manufacturers try to keep engines running as lean as possible as often as they can in order to improve emissions, mileage and power. Thus they build in significant safety margins. Detonation isn't actually caused by a lean condition; it is a result of a lean condition. Gasoline actually acts as a suppressor to the ignition event. Leaning out under hard throttle causes temperatures to rise which cause lean mixtures to pre-ignite, but the temperatures are the cause of pre-ignition.
The S-AFC is a fuel computer that adjusts fuel/air ratio by modifying the airflow meter/MAP sensor signal. The S-AFC features a user-definable, eight-point, adjustable fuel curve that can be set in 500-RPM increments. The range of fuel adjustment is +/- 50% at each of the user-defined setting points. On hot-wire vehicles, the Deceleration Air Flow Correction function is capable of curing the erratic idle and stall problems associated with open atmosphere blow-off valves on hot-wire airflow meter systems. The S-AFC is capable of monitoring and replaying the following data channels in Numerical, Analog Meter and Graph displays: Intake Manifold Vacuum/Boost Pressure, Air Flow Capacity, Intake Manifold Pressure, Karmann Frequency, Engine RPM, Throttle Position, and Air Flow Correction %.
http://www.nissanperformancemag.com/may03/project_qg18de/images/safc-scr3.jpg
"The Apexi S-AFC is a highly versatile fuel computer which allows remapping of the fuel using the airflow /air pressure sensor fitted to most vehicles." - Apexi
Monitor Mode: Allows monitoring of up to 4 channels at one time. Also it allows tracing of AVC-R monitor function.
http://www.nissanperformancemag.com/may03/project_qg18de/images/safc-scr1.jpg
Setting Mode: Allows user to adjust air/fuel ratio through Hi and Lo Throttle maps. Other features like throttle percentage settings, rpm point settings, and deceleration airflow corrections are adjustable through the setting menu.
Etc. Mode: The etcetera menu is for adjusting the variables that are required for the S-AFC to properly adjust fuel (i.e. # of cylinders, throttle position sensor type, sensor type, etc.)
http://www.nissanperformancemag.com/may03/project_qg18de/images/safc-scr2.jpg
Monitor Mode: 1,2,3,4 Channels
Up to four data channels can be selected for monitoring:
1. Air Flow
2. Throttle Position
3. Intake Manifold Pressure
4. Engine RPM
Up to four of these parameters can be monitored in three different ways:
Numerical
Analog Meter
Graph Display
If monitored numerically, the user can see a peak hold value for the chosen parameter by pressing the up key.
If monitored in analog meter mode, up to two meters can be displayed at one time. By pressing the up key, the analog meters will hold the peak value.
If under 3 or 4 channel mode, only the first two channels will be displayed. If monitored in graphic display mode, the S-AFC can start "sampling" or memorizing data channels by pressing the up key.
The memorized graph can then be replayed by pressing the right key. Anytime during replay by pressing the right key again, the display can be paused. To review any part of the memorized graph, the user can push the left key during replaying. Anytime during backwards replay, the left key can be pressed to pause the display. If monitoring one channel, then the last 60 seconds can be replayed. If monitoring two channels, then the last 30 seconds can be replayed. If monitoring three channels, then the last 20 seconds can be replayed. If monitoring four channels, then the last 15 seconds can be replayed.
Monitor Mode (2D Trace Mode)
Up to five parameters can be monitored, but only one at a time:
1. Air Flow Usage
2. Intake Manifold Pressure
3. Karmann Frequency
4. Throttle Percentage %
5. Air Flow Correction
The 2D Trace Mode displays one user-selected parameter versus engine RPM. The horizontal scale being engine RPM and the vertical scale being the user-selected parameter. There are three ways to view the 2D Trace. One way is a simple cursor that floats around the screen showing what the user-selected value is. The second way to view the graph is with a 10 point floating trail to show the trend of the user-selected value. The third way is to view with a "Ghost Map" trace. The "Ghost Map" shows wherever the cursor has been and does not clear until the user clears the screen.
This on a sentra but the same basic theory applies across the board:
http://www.nissanperformancemag.com/may03/project_qg18de/images/pImgLeft_electronics_safc1.jpg
The S-AFC intercepts the signal from the airflow meter before it gets to the ECU (Engine Control Unit) and adjusts it to trick the ECU into thinking it's getting more or less air in order to increase or decrease the fuel it adds. It gives you direct control over the amount of fuel going into your engine. Of course, you then have the potential to damage your engine if you try and tune it without an air/fuel meter hooked up.
http://www.nissanperformancemag.com/may03/project_qg18de/images/safc00.jpg
If you know your car is running rich or lean at certain rev ranges and throttle positions, then you are not getting the full power potential from your engine. After having our stock intake manifold Extrude Honed, Project QG18DE was running a very unfavorable air/fuel ratio. It was so unsafe we didn't even want to dyno the car for fear of causing major damage to the motor under high RPM. Therefore, the need for an air/fuel controller was evident.
The air/fuel ratio is a very common source of confusion to many people. It is the ratio of air to fuel exiting from the engine and a good measure of engine tune. The air/fuel ratio is commonly represented as a single numeral as in 14.7. This actually represents the number of air particles exiting per single fuel molecule (ie.,14.7:1). The 14.7:1 just mentioned is actually what is called stoichiometric, or the ideal air/fuel ratio at which temperatures are controlled and fuel economy is optimized. The air/fuel ratio affects the heat generated during the combustion phase of the engine cycle. Fuel acts as a cooling agent for the cycle. Having a numerically lower air/fuel ratio (less than stoichiometric) is considered to be a RICH condition (ie., richer in the amount of gas exiting) and will result in lower exhaust gas temperatures (EGTs). Conversely, leaning out the mixture by injecting less gasoline causes the overall exhaust gas temperatures to rise. A change from a lean to a rich mixture can cool the exhaust charge by as much as 400 degrees Fahrenheit. The air/fuel ratio can be monitored by an air/fuel gauge or an exhaust gas temperature gauge. An A/F gauge shows the instantaneous mixture while an EGT gauge shows the actual temperatures in the engine to check its condition.
Some common air/fuel ratio misconceptions:
1) Running an extremely rich air/fuel ratio creates more power:
This is a good one for novices who think that you need to consume every last bit of air going into an engine. Actually an engine spits out most of the air it ingests as the ignition cycle for a particular cylinder is far too small and short to effectively utilize the entire air mixture. When high-powered turbo cars or N/A (naturally aspirated) cars run extremely rich mixtures, it is to keep cylinder temperatures down. Frequently cars gain power as they run more optimized air/fuel ratios, typically slightly richer than stoichiometric. In addition, rich mixtures can wear out sensors, waste gas, and clog your catalytic converter. If it were true that more gas always equaled more power, racecars would simply dump fuel directly into the ports instead of worrying about metering. Tuning is the key!
2) Going lean creates an 'instant detonation' condition:
In the case of street engines, this just isn't true. Manufacturers try to keep engines running as lean as possible as often as they can in order to improve emissions, mileage and power. Thus they build in significant safety margins. Detonation isn't actually caused by a lean condition; it is a result of a lean condition. Gasoline actually acts as a suppressor to the ignition event. Leaning out under hard throttle causes temperatures to rise which cause lean mixtures to pre-ignite, but the temperatures are the cause of pre-ignition.
The S-AFC is a fuel computer that adjusts fuel/air ratio by modifying the airflow meter/MAP sensor signal. The S-AFC features a user-definable, eight-point, adjustable fuel curve that can be set in 500-RPM increments. The range of fuel adjustment is +/- 50% at each of the user-defined setting points. On hot-wire vehicles, the Deceleration Air Flow Correction function is capable of curing the erratic idle and stall problems associated with open atmosphere blow-off valves on hot-wire airflow meter systems. The S-AFC is capable of monitoring and replaying the following data channels in Numerical, Analog Meter and Graph displays: Intake Manifold Vacuum/Boost Pressure, Air Flow Capacity, Intake Manifold Pressure, Karmann Frequency, Engine RPM, Throttle Position, and Air Flow Correction %.
http://www.nissanperformancemag.com/may03/project_qg18de/images/safc-scr3.jpg
"The Apexi S-AFC is a highly versatile fuel computer which allows remapping of the fuel using the airflow /air pressure sensor fitted to most vehicles." - Apexi
Monitor Mode: Allows monitoring of up to 4 channels at one time. Also it allows tracing of AVC-R monitor function.
http://www.nissanperformancemag.com/may03/project_qg18de/images/safc-scr1.jpg
Setting Mode: Allows user to adjust air/fuel ratio through Hi and Lo Throttle maps. Other features like throttle percentage settings, rpm point settings, and deceleration airflow corrections are adjustable through the setting menu.
Etc. Mode: The etcetera menu is for adjusting the variables that are required for the S-AFC to properly adjust fuel (i.e. # of cylinders, throttle position sensor type, sensor type, etc.)
http://www.nissanperformancemag.com/may03/project_qg18de/images/safc-scr2.jpg
Monitor Mode: 1,2,3,4 Channels
Up to four data channels can be selected for monitoring:
1. Air Flow
2. Throttle Position
3. Intake Manifold Pressure
4. Engine RPM
Up to four of these parameters can be monitored in three different ways:
Numerical
Analog Meter
Graph Display
If monitored numerically, the user can see a peak hold value for the chosen parameter by pressing the up key.
If monitored in analog meter mode, up to two meters can be displayed at one time. By pressing the up key, the analog meters will hold the peak value.
If under 3 or 4 channel mode, only the first two channels will be displayed. If monitored in graphic display mode, the S-AFC can start "sampling" or memorizing data channels by pressing the up key.
The memorized graph can then be replayed by pressing the right key. Anytime during replay by pressing the right key again, the display can be paused. To review any part of the memorized graph, the user can push the left key during replaying. Anytime during backwards replay, the left key can be pressed to pause the display. If monitoring one channel, then the last 60 seconds can be replayed. If monitoring two channels, then the last 30 seconds can be replayed. If monitoring three channels, then the last 20 seconds can be replayed. If monitoring four channels, then the last 15 seconds can be replayed.
Monitor Mode (2D Trace Mode)
Up to five parameters can be monitored, but only one at a time:
1. Air Flow Usage
2. Intake Manifold Pressure
3. Karmann Frequency
4. Throttle Percentage %
5. Air Flow Correction
The 2D Trace Mode displays one user-selected parameter versus engine RPM. The horizontal scale being engine RPM and the vertical scale being the user-selected parameter. There are three ways to view the 2D Trace. One way is a simple cursor that floats around the screen showing what the user-selected value is. The second way to view the graph is with a 10 point floating trail to show the trend of the user-selected value. The third way is to view with a "Ghost Map" trace. The "Ghost Map" shows wherever the cursor has been and does not clear until the user clears the screen.