A'PEXi S-AFC & 700cc Injectors
- Thread starter Rishi
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A
Anonymous
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The S-AFC works by fooling the input air flow signals to the ECU. To lean the engine out it tells the ECU it's sucking in less air than it actually is. This causes the ECU to switch down to a lower load cell in it's fuel map, but also causes the ECU to select the corrisponding lower load cell in the spark advance map. Less engine load = more timing advance.
This is fine for small adjustments, but even switching to just 550cc injectors becomes a problem and the only safe way to tune them is to add 10% to the fuel map, then lower the fuel pressure until the idle mixture comes in spec. You can then safely lean out 10% putting the AFC on a 0 adjustment, and add fuel where you need it.
To use an AFC to control 700cc injectors would just be stupid. For a start you only have 50% +/- adjustment, and the extra timing you would add by leaning the mixture will quickly lead to massive detonation and a destroyed engine.
Don't be a cheap skate and go standalone EMS.
This is fine for small adjustments, but even switching to just 550cc injectors becomes a problem and the only safe way to tune them is to add 10% to the fuel map, then lower the fuel pressure until the idle mixture comes in spec. You can then safely lean out 10% putting the AFC on a 0 adjustment, and add fuel where you need it.
To use an AFC to control 700cc injectors would just be stupid. For a start you only have 50% +/- adjustment, and the extra timing you would add by leaning the mixture will quickly lead to massive detonation and a destroyed engine.
Don't be a cheap skate and go standalone EMS.
A
Anonymous
Guest
If you tell the AFC to add 15% fuel, it will do. If you tell it to remove 15% fuel, it will do that too. Injector control isn't the problem here, the problem is what happens to the spark advance.
Remember that the S-AFC alters the signal sent from the airflow meter to the ECU. The ECU has a preprogrammed map for both spark advance and injector opening times. It uses the reading from the air flow meter to calculate load, and the engine RPM, then looks up the correct fuel and advance settings from the preprogrammed maps. If you alter the air flow signal to make the ECU read a lower load cell in the fuel map, at the exact same time you make the ECU read a lower load cell in the spark advance map.
If you pull 20% fuel using an AFC by fooling the ECU in to thinking 20% less load is on the engine, depending on load you could add 10 degrees spark advance. Off boost you can run as much advance as you like without ever running in to a problem with detonation, however on boost the total advance is always knock limited. A good example of this would be,
No AFC, 440cc injectors, 15psi boost, 6500rpm = Injector time 14.6ms / Spark advance 22 degrees (total advance) AFR= 11.8:1
S-AFC pulling 40% fuel 700cc injectors, 15psi boost, 6500rpm = Injector time 8.76ms Spark advance 32 (total) AFR=11.8:1
That extra 10 degrees advance will cause the engine to detonate, and no, water injection isn't enough to prevent it.
You CAN NOT safely run 700cc injectors with just an S-AFC, you will need something to also control the timing too. By the time you've forked out for an AFC and ITC (timing controller) you could have already bought a standalone ECU like the SDR.
Don't try to save money on engine tuning because it always works out more expensive in the long run. If you are at the point where you need bigger injectors, you are also at the point where to make the most of your engine safely you need a stand alone ECU.
700cc injectors have enough fuel to make nearly 480 wheel horse power, so say if you run them safely at 85% duty that's still nearly 400hp at the wheels. To run that power you will have to run upwards of 26psi boost on at least a 50 trim T3/T4 (or GT30 for example). Our standard ECU only has timing maps up to around 13psi boost, after that point injector duty is maxed out and the spark advance holds it's total advance. To stop detonation you will have to pull timing from the top of the map anyway at that boost level, so making matters worse by having an AFC adding more advance will destroy your engine in no time.
An Apexi S-AFC is not a proper tuning tool, it's only good for making small adjustments to standard injectors. The second you start to pull more than 15% fuel, you will start to have problems with excessive advance. If you need further proof I suppose I could post up some maps from other cars I have tuned.
Remember that the S-AFC alters the signal sent from the airflow meter to the ECU. The ECU has a preprogrammed map for both spark advance and injector opening times. It uses the reading from the air flow meter to calculate load, and the engine RPM, then looks up the correct fuel and advance settings from the preprogrammed maps. If you alter the air flow signal to make the ECU read a lower load cell in the fuel map, at the exact same time you make the ECU read a lower load cell in the spark advance map.
If you pull 20% fuel using an AFC by fooling the ECU in to thinking 20% less load is on the engine, depending on load you could add 10 degrees spark advance. Off boost you can run as much advance as you like without ever running in to a problem with detonation, however on boost the total advance is always knock limited. A good example of this would be,
No AFC, 440cc injectors, 15psi boost, 6500rpm = Injector time 14.6ms / Spark advance 22 degrees (total advance) AFR= 11.8:1
S-AFC pulling 40% fuel 700cc injectors, 15psi boost, 6500rpm = Injector time 8.76ms Spark advance 32 (total) AFR=11.8:1
That extra 10 degrees advance will cause the engine to detonate, and no, water injection isn't enough to prevent it.
You CAN NOT safely run 700cc injectors with just an S-AFC, you will need something to also control the timing too. By the time you've forked out for an AFC and ITC (timing controller) you could have already bought a standalone ECU like the SDR.
Don't try to save money on engine tuning because it always works out more expensive in the long run. If you are at the point where you need bigger injectors, you are also at the point where to make the most of your engine safely you need a stand alone ECU.
700cc injectors have enough fuel to make nearly 480 wheel horse power, so say if you run them safely at 85% duty that's still nearly 400hp at the wheels. To run that power you will have to run upwards of 26psi boost on at least a 50 trim T3/T4 (or GT30 for example). Our standard ECU only has timing maps up to around 13psi boost, after that point injector duty is maxed out and the spark advance holds it's total advance. To stop detonation you will have to pull timing from the top of the map anyway at that boost level, so making matters worse by having an AFC adding more advance will destroy your engine in no time.
An Apexi S-AFC is not a proper tuning tool, it's only good for making small adjustments to standard injectors. The second you start to pull more than 15% fuel, you will start to have problems with excessive advance. If you need further proof I suppose I could post up some maps from other cars I have tuned.
K
KRS
Guest
That was pretty educational Ben, Thanks for taking the time out to explain that 
Some good stuff there Ben 8) completly skipped my mind that the timing is also calculated off the airflow readings I got around that by lowering the base timing (with the dizzy)which had the desired affect when on boost but obviously off boost suffered due to it
As i've said before about mine when it ran this setup it ran ok and produced the bhp but it didn't run smoothly and weren't exactly nice to drive
With the power fc fitted it just runs so much smoother and drives so much better even on the base map 8) don't bother with the s-afc as by the time you've had it fitted and set up etc you'll be looking at nearly power fc money anyway and you'll like driving the car a whole lot more aswell
I got around that by lowering the base timing (with the dizzy)which had the desired affect when on boost but obviously off boost suffered due to it As i've said before about mine when it ran this setup it ran ok and produced the bhp but it didn't run smoothly and weren't exactly nice to drive
With the power fc fitted it just runs so much smoother and drives so much better even on the base map 8) don't bother with the s-afc as by the time you've had it fitted and set up etc you'll be looking at nearly power fc money anyway and you'll like driving the car a whole lot more aswell
A
Anonymous
Guest
Running a chip setup for 550cc injectors is fine to use 550cc injectors. I don't believe it's widely known but some early Nissan ECU's including the R32 skyline ones are actually reprogrammable with specialist software by a company called Techrom. The early ECU's were only fitted with either 16k or 32k flash memory so the maps didn't have a very high resolution, but you could alter the fuel and advance maps for greater performance and to support larger injectors without the need to go standalone. At present the only people I know who still use the Techrom software is a company called ATS Racing in the US.
Running a generic chip for larger injectors won't make as much power from your engine as a custom map from a standalone ECU.
Running a generic chip for larger injectors won't make as much power from your engine as a custom map from a standalone ECU.