SAFC-II

SON240sx Automotive
1

his post is inspired but the AVC-R thread in the FAQ.

i have learned how to use some of the functions of the SAFC-II, but i know for sure that there is SO MUCH MORE potential to be had out of it.

for those who have used it and tuned it, could you please share as much info as you cna on your techniques.

links to others would be good to.

also, there is a problem with my SAFC, it is monitoring my RPM wrong.

for example, at idle my tach says 800, but the SAFC will say 550.

the gaps gets even bigger as i get into higher rpm, and i cant make the SAFC read higher than 4100 RPM even when i am at redline

WHAT THE DEAL with that yo?

2

the difference in RPM is normal… my VAFC (in my lude) reads about 7700rpm when the stock tach is at 8100rpm.

vafc/safc = accurate

3

bing you have your tach setup wrong in the s-afc manual you have it to 4 when it should be 2 or something like that .i cant remember exactly.

decel air is the only feature i couldn’t figure out on the S-AFCII but id like to get it figured out. A wideband would defiantly help.

4

It not really function related but I think this post does well to explain how the SAFC works for our applications… specifically SR with z32 MAF and larger injectors.

Stolen from Enthalpy on FreshAlloy

Ok heres the deal:

Stock Z32 MAF = 530 WHP
Stock SR MAF = 260 WHP

so the Z-32 MAFS can flow 2.04 times as much air as the stock maf. this is great for High HP cars. so IN THEORY say your car is cruising down the road and you are making 50 hp under a light acceleration. Now airflow meters are not a linear response but have more of a exponential response. but for this example we will assume a linear response to make things easier…when you get into the exponential response you need to include a conversion function that is beyond the scope of this response…and in the end makes no difference in the final answer (thanks regis)…

So where were we? oh yeah 50 Hp…so by the conversion factor and assumed linear response above the SR maf would read .96 volts and the Z32 would read .47 volts. Now for your car to run correctly using the Z-32 and stock injectors the ECU needs to be seeing .96 volts. the S-AFC knows the response multiplier and multiplies the incoming MAF voltage (.47 from the Z-32) by 2.04 and sends out a .96 volt output to the ECU…and you drive down the road with no problem.

then you lay into full power…say for this example your car has 300 Hp capacity with it’s ncie s-15 BB turbo, but stock injectors (good to 270ish WHP) you lay into it and at 260 Hp the stock MAF would max out (5.0 V) and this is what the ECU would need to see to make the car run right. the Z-32 would now be outputting 2.45 volts into the S-AFC. it multiplies by 2.04 and you get 5.0 Volts and your car shuts down. The ECU sees anything greater than 5.0V as a fault and shuts the system down until proper voltages are seen (maybe a grace window to 5.12V as stated earlier). So how did i run 380 HP on a S-AFC and a stock ECU??

Injector correction!!

so being smart and realizing you have 300 Hp on tap but only 270HP worth of injector you go out and buy new injectors. A bright Yellow new set of new Tomei 555cc Side feeds…life is good! you go back and do the calculation for baseline correction for the injectors.

(370/555) - 1 = correction factor = -33%

so you go in and set all your high and low throttle settings to -33%. and you go drive your car!! now in the real world the settign once tuned on a wideband would be much different due to ECU mapping…on my car with the described setup there were places where i was runnign -45% correction to get a desired 12.0:1 AFR…but that is irrelevant for a 300 HP car such as this example!!

so back on the highway light acceleration 50 Hp…for the car to run properly the injectors need to see 2/3 of the on time of the stock 370’s at this power, and thus 2/3 of the expected original MAF voltage…if you dont understand this i can clarify in another post. so you would usually have .96v coming in…but were on the Z-32 so we have .47. the S-afc performs the airflow conversion of 2.04 and you have .96V. next the S-afc performs the programmed correction factor of -33% that you entered. so you have

0.96 - (0.96 * .33) = output to ECU = .64V

now as you can tell that is exacly 2/3 of the ORIGINAL (stock maf/injector) air flow that would have been needed to run the car. and you drive perfectly down the road…

then you come across that pesky mullett in the 5.slow Rustang and you decide to let the SR breathe and show this neaderthal who is king of the road. you wind your SR all the way out to it’s full 300Hp potential and leave mulletore wondering what happened…but how did it work??

so you went all the way to 300 HP. on a stock MAF that would have been 5.77 volts…not possible. and as you know the ECU would have shut you down at 5.0 V anyway. but we have the Z-32 and we were runnign bigger injectors so here is what we had!! Z-32 output was 2.83 volts…Airflow meter corection is 2.04 and the Injector tuning had you at -33%. so our final voltage to the ECU was as follows…

2.83 * 2.04 = 5.77 (same as before)

now for injector correction

5.77 - (5.77 * .33) = final output to ECU = 3.87V

now as we discussed earlier this needs to be 2/3 of the original injector on time … and it is very close (off by a few thousnaths of a volt). the ecu has no problem with a 3.87 Volt input and you are merrily going along leaving the mullet junky in the dirt!!

now…you get a good bonus at work and decide to upgrade the turbo!! you put on nice GT25R and you are now capable of 390 Hp (if only you could find that mustang again and really give him a lesson!!) so you go out there and stand on the gas!!. spool that baby upa nd right before redline the car shuts off. Agrhh…your frustration is un-paralleled by anything known to man!! why you ask yourself as you cruise back to the garage in low boost mode!! lets do the calcs!!

390 Hp on a Z-32 would produce 3.68V out of the MAF…it goes into the S-AFC

times 2.04 = 7.50V

Injector correction = -33% so

7.50 - (7.50 * .33) = final output to ECU = 5.02V

oops theres our problem the ECU shut us down again! its time for a re-program or bigger injectors…but at this point you are so far away fromt eh origianl power levels…i suggest just a reprogram.

Hopefully that clarifies any misconceptions about the S-afc and S-afc2!! and how they work!!

5

you can just run 555cc injectors and a Z32 mafs.

555cc x 4 = 2220

370 x 6 = 2220 > Z32 has 6 370cc injectors, and runs basically the same AFRs throughout the powerband. So put in a Z32 mafs and 555cc injectors and the car will run like stock.

6

reads proper RPM now,

sasha you da man

7

wow i just learned how it works but i dont even have one yet. :lol:

8

Has anyone does this?

9

it should work in theory, the only difference is that the maps might be off if its not linear.

10

ive been thinking about it, since the voltages would be different, even though it would be dumping in proportionally the same amount of fuel, it would be at a different load rating on the fuel map meaning the signal to the injector would be different. I’m sure it would be close until you started making a lot of power, thats when you would notice the car running off.

11

But if my last post is correct than what hes saying in the S-AFC post is wrong too, because its assuming the MAFS voltage is linear:

"so back on the highway light acceleration 50 Hp…for the car to run properly the injectors need to see 2/3 of the on time of the stock 370’s at this power, and thus 2/3 of the expected original MAF voltage…if you dont understand this i can clarify in another post. so you would usually have .96v coming in…but were on the Z-32 so we have .47. the S-afc performs the airflow conversion of 2.04 and you have .96V. next the S-afc performs the programmed correction factor of -33% that you entered. so you have

0.96 - (0.96 * .33) = output to ECU = .64V "

I would try doing the Z32 and 550s and run it on a wideband and see what happens, and use the S-AFC to fine tune the system. The reccomendations in this article are stupid, their causing you to be near 50% correction all the time which is the max of the S-AFC. What if you need to tune more? The idea of the S-AFCII is to set it up so that 0% correction factory is the same fuel curve as stock, none of this -33% across the board bullshit. Thats why they give you options for different MAFS and ECU imputs.

I’m going to stand behind my original statement just not 100%, but please someone give this a try! Grab a wideband and try it out.

Set the MAFS and ECU the same as you have put your Z32 mafs and 550s or 555s in and see how teh car runs, it will probobly need tuning ESSPECIALLY above where the old mafs ran out since Nissan (more than likely) didnt map out the fuel curve for airflow above what the stock mass air flow could read.

12

Has anyone does this?[/quote]

Yes and it works like butterscotch… 15psi all day long runnning @ ~12:1