EdgeminSH

I read the whole thing about setting up a SAFC/VAFC Im confused about something he said hopefully you all can help me out
He said

The scale for common injector sizes used is 5% for 440-450cc, 4%, 390cc, 3% for 310cc.. then subtract 1 percent per 500 RPM increase. This will give us are starting point. For a boosted application, running stoichiometric is dangerous because of the high volume of air. To "play it safe", you want to run a bit on the stoich/rich side, so we increase fuel flow by 1% per 1000 rpms,

My question is. When you subtract 1 percent per 500 rpms what do you do when you get to 0 percent? do you just then start increasing a percent per 1000 rpms? Just making sure i have it right correct me if im wrong

TurboEF9

Yes, but as you're decrease by one, you're adding by 1% per 1000 RPMs, so like this..

46% + 5% = 41% @ 1000
40% @ 1500
40% @ 2000
40% @ 2500
39% @ 3000
39% @ 3500
38% @ 4000
..and so on..

john duh

I've also heard that the SAFC changes your timing. Is it that as you go lower in your percentage settings that your timing will advance? Or is it the other way around?

Can someone clear this up?

TurboEF9

Please read the Engine Management FAQ, section 2, question 3.

willahlborn

All the SAFC does is modify the signal going to your ECU from the MAP sensor. It can tell your ecu that there is more air in your intake than there actually is, forcing the ecu to pump more fuel. It also uses the TP sensor to fine tune things, but that is the gist of it.

TurboEF9

...that's backwards...

When used with as the "AFC Hack", it actually makes your ECU think there is LESS air going into your manifold. This makes it read from leaner parts of the fuel map ("pumping less fuel"). In doing this it indirectly advances your ignition timing by shifting over to move advanced region of the ignition map. "But if it's leaning your car out, how does it let you give more fuel for boost?" You compensate with larger injectors. Larger injectors will flow more fuel at the same pulse widths of smaller injectors, simply because they're larger. This is how the "AFC Hack" works.