[gurov]

this is a copy of my post from the vboard, figured i'll post it here for review.

an explanation of how safc2 determines and uses both hi/low throttle maps to calculate the adjustment needed.

it interpolates intermediate values.
it goes off the assumption that throttle plate can be somewhat related to load on the engine.

i am also going off the assumption that safc is doing this in a linear fashion, it could be exponential, i can do a writeup on the exponential adjustment interpolation if someone thinks it's not linear.

so for example imagine this situation:
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...
someone correct me if my math is off:

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 (5+(20*-0.66))
55% throttle both maps are used adjustmen = -11.5 (5+(25*-0.66))
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 60 - 80 or something like that, i keep changing them pretty often as i play with the safc.


hope this helps.

*edit: modified some of the math, not using abs() anymore, a more general approach*

 

[gurov]

i threw together an excel sheet with these calculations that you can plug your low and high throttle positions, and adjustments on both maps. keep in mind, this is for a single rpm NE point.

http://gurov.us/safc2.xls

another thing to keep in mind is that adjustment RPM points will also have an effect on how interpolation is done. it probably works the same way this interpolation does.

((adj2-adj1)/(ne2-ne1))*currentrpm

where ne2 > currentrpm > ne1
adj1 = adjustment @ ne1
adj2 = adjustment @ ne2

 

[TeknoPunk]

subscribing to thread

 

[AntonToo]

between - both maps are used on a sliding scale.

How did you get to this conclusion?

 

[HumboldtBlazer]

How did you get to this conclusion?

Yeah, I can figure some of the math out of course but the whole concept is not clicking yet with me. Can you explain this ina little more laymans terms?

 

[JohnO]

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.

Gurov that was a nice work but to be honest it is pretty clearly stated in the AFC manual that this is the case hopefully anyone who is tuning an AFC knows these factors.

The formula to make is simple is at any given rpm point you have plotted
(high TP correction percentage - ( lo tP correction percentage)) * (current TP - lo tp setting)/ (Hi TP setting - Lo TP setting) + ( Lo TP correcton percentage) = current correction factor ..


regardless .. while nice to know it is not much help to us since we really want no correction factors for lo setting unless we have changed fuel pressure or injector sizing ...

 

[JohnO]

How did you get to this conclusion?

its stated in the manual

 

[HumboldtBlazer]

Gurov that was a nice work but to be honest it is pretty clearly stated in the AFC manual that this is the case hopefully anyone who is tuning an AFC knows these factors.

The formula to make is simple is at any given rpm point you have plotted
(high TP correction percentage - ( lo tP correction percentage)) * (current TP - lo tp setting)/ (Hi TP setting - Lo TP setting) + ( Lo TP correcton percentage) = current correction factor ..


regardless .. while nice to know it is not much help to us since we really want no correction factors for lo setting unless we have changed fuel pressure or injector sizing ...

THANK YOU! Very comprehensive. That made sense to me.

 

[pugnex]

Has it been determined all the conditions on which the ECU goes from closed to open loop?

 

[JohnO]

Has it been determined all the conditions on which the ECU goes from closed to open loop?

Really can depend on conditions and load .. but pretty much anytime you are past 60% TPS you are in open loop .. that is where i would set my lo and i would set my hi setting at 61% ... we basicly will only uset this for open loop in car with bolt on's ..

 

[HumboldtBlazer]

Really can depend on conditions and load .. but pretty much anytime you are past 60% TPS you are in open loop .. that is where i would set my lo and i would set my hi setting at 61% ... we basicly will only uset this for open loop in car with bolt on's ..

So you set your low @ 60% and your high @ 61%?

 

[JohnO]

THANK YOU! Very comprehensive. That made sense to me.

even easire hum and the way i do it is ..

i find the percentage that my current TP is in refference to the difference of my lo and high settings ... so baiscly if your lo is 20%TPS and your hi is 80%TPS then 50% TPS would fall right at the 50% of the difference .... 35%tps would be would be 25% of the difference .. so on and so on ..

Then you just find the same percentage of difference between the 2 correction factors in that given RPM .. so lets say at 4k we are set 0 at lo and -10% at hi ... then using the exmaple above at 50% tps we would only have a -5% correction factor .. and at 34% tps we would only have a -2.5% correction factor .. so on .. so on ..

 

[JohnO]

So you set your low @ 60% and your high @ 61%?

i would .. but sometimes that can confuse an AFC ( or at least i have seen that give one problems when i installes Jpalms here on the boards) .. so i spread it a little futher .. so you can do like 55% lo and 65% hi .. or 60% lo and 70% hi..

 

[HumboldtBlazer]

i would .. but sometimes that can confuse an AFC ( or at least i have seen that give one problems when i installes Jpalms here on the boards) .. so i spread it a little futher .. so you can do like 55% lo and 65% hi .. or 60% lo and 70% hi..

You da man JohnO, you da man!

 

[gurov]

i didn't read the manual, i just pretty much guessed on the math, that's how i would make it work if i were to make a device like that.

 

[tbuh]

Would someone give me a clear answer as to whether or not we should have lo-throttle settings set on our S-AFC's?

 

[pugnex]

As far as I know...no. The ECM does a pretty damn good job being at optimum A/F ratios, and by using the SAFC along with the ECM maps, you'll just be pissing the ECM off.

 

[gurov]

Would someone give me a clear answer as to whether or not we should have lo-throttle settings set on our S-AFC's?

i don't have any corrections in the low map or below 3000 rpm right now.
the ecu does a good job at correcting for injector sizes, most of the time i'm running with -25% longterm fuel trim as reported by obd2

 

[AntonToo]

As far as I know...no. The ECM does a pretty damn good job being at optimum A/F ratios, and by using the SAFC along with the ECM maps, you'll just be pissing the ECM off.

How do you explain Specs running so rich stock?

 

[AntonToo]

i didn't read the manual, i just pretty much guessed on the math, that's how i would make it work if i were to make a device like that.

Thats my motto: "When ALL else fails...refer to manual"