Safc-II Why Not?

[AshTsi]

Okay guys, need help so my dad will stop hassling me. I know that with a Safc-II you shouldn't go over 660cc injectors, i tryed explaining this to my father but couldn't get the point across. I've been telling him about Dsmlink and why i need it, but he keeps arguing about why i should just be able to use the Safc-II.

Please dont chop me down for asking i just dont know how to explain it to him so im looking to you guys for a detailed answer. Thanks!!

This is his question:: If you have the 16g with 660cc's and can tune it, why wont it work using a larger turbo with larger injectors on say a 2.3L. Because your using basically using the same system on the same motor just everything a bit bigger, the ECU is still going to adjust timing, rich/lean. shouldn't it still run? why wouldn't it still function properly? It might not be the most optimal using Safc-II over dsmlink but shouldn't it still function fine?


So thats his question, he knows with Dsmlink you have more tuning capability. just not why it wouldn't work with the other setup, and i dont know enough about tuning to explain in detail

Thanks guys!!
~Ash

 

[kenamond]

SAFC deceives the ECU about the air speed Hz signal coming from the MAS. If you have larger injectors, you have to lie to the ECU about airflow by intercepting the Hz signal, decreasing it, and passing on the modified value to the ECU. The ECU will then pulse the injectors for a shorter period which is what you need for the larger injectors. You do this for several RPM points in order to adjust the "lie" over the rpm range.

The ECU uses the Hz signal (airspeed), barometric pressure, and intake air temperature to compute the mass air flow rate through the MAS (most loggers show this in lb/min of air). The ECU then takes the rpm value and the mass air flow value to calculate load which is the mass of air entering each cylinder during an intake stroke. Load is usually reported in units of g/rev.

The problem with SAFC is that load is used by the ECU for both fuel and *timing advance*. If you lie about airflow so that the ECU thinks there is less of it, it advances your timing moreso than if you weren't lying to it. The larger the injectors, the bigger the lie, and the more advanced your timing goes. This can raise knock count.

That's my understanding of it. There's also a difference in dead times and stuff like that, but I'm not familiar with those details.