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Understanding safc high/low throttle point settings

4020 Views 3 Replies 2 Participants Last post by  str8rpn
an explanation of how safc2 determines and uses both hi/low throttle maps to calculate the adjustment needed.

It goes off the assumption that throttle plate can be somewhat related to load on the engine.


so for example:
lo th=30
hi th=60

lo map @ 4000 rpm = +5
hi map @ 4000 rpm = -15

lets look at the adjustments it will make, for simplicity sake, lets assume that the engine is rotating at 4000 rpm regardless of throttle posititon:

0 throttle - lo map only is used , so +5 adjustment to airflow
10 throttle - lo map only is used, +5 adjustment
20 throttle - lo map only is used , +5 adjustment
30 throttle - low map only is used, +5 adjustment
40 throttle - this is where it gets a bit complicated, it will use both of the maps and interpolate the value between lo and hi adjustment based on the throttle...

total adjustment points = hi - lo = -15-(+5) = -20
throttle difference = hi th - lo th = 60 - 30 = 30
adjustment points per throttle % = -20 / 30 = -0.66


adjustment at 10% above lo position = 10 * -0.66 = -6.66% towards hi throttle map
so at 40% throttle the adjustment will be 5+(-6.66)

so... 40% throttle both maps are used adjustment = -1.66
50% throttle both maps are used again, adjustment = -8.2
55% throttle both maps are used adjustmen = -11.5
60% hi map only is used adjustment = -15%
70% hi map only adjustment = -15%
and so on.

to sum this up

below lo throttle, only lo throttle map is used
above hi throttle, only hi throttle map is used
between - both maps are used on a sliding scale.

mine... are set at 55 lo - 85 hi.


hope this helps.
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thats confusing as shit but i think i kinda got it. i just dont understand what the +5, -15 means exactly...what should the number settings and the rpm settings be for a turbo specv? i know i can change my rpms as well on the lo/hi maps
every car is different, i cant tell u what your settings should be. those +5,-15 where examples.

another example, maybe you'll get this one.

lets say u want to add fuel, for example, +10 at 1000 rpms low and +20 at 1000 rpms high setting. And you have your throttle point to be set to 10%lo 50%hi.

That means you will have +10 at 1000k rpms if you do NOT push the gas pedal more then 10%. if you go past 10% it will start getting the corrections of your high settings.

+10 lo @ 1000k rpms with 8%throttle will remain +10 cuz u havent pressed the gas past 10%. Lets say u push the gas alil harder to 15% then u will see +15 on ur safc.

thats not that great of an example but think of it this way, if you have your hi set to be 50% that means it will not get your HI corrections until you press the gas half way. If you set your HI at 80% it will not get the HI corrections till u press the gas pedel past 80%.
okay that makes more sense...
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