safc or vafc?

[b6t power]

hey im looking in to getting a afc thing for my car but im not to sure what one i need... from what i can tell there is 2 diffrent types, a vafc and a safc... whats the diffrence between them?

[Turpro]

Vafc has controls for vtec(honda/acura). You'd want a safc

[Lex]

Hey, you're local to me!

The big question is, why do you need an SAFC? Running larger injectors?

[concealer404]

Don't once you hit 100% wot, these cars go into open loop anyways, making an AFC useless?

[b6t power]

Vafc has controls for vtec(honda/acura). You'd want a safc

but would a vafc work? couldnt i just leave the vtec wires unpluged or somthing???

Hey, you're local to me!

The big question is, why do you need an SAFC? Running larger injectors?

im trying to use a na ecu to run a turbo motor and i need the afc to get it running at the right a/f... (this is what i have been told...)

Don't once you hit 100% wot, these cars go into open loop anyways, making an AFC useless?

is that true? it seams that there is alot of people on here that have them and they work ok...

[concealer404]

but would a vafc work? couldnt i just leave the vtec wires unpluged or somthing???

Sure. Or better yet, use the VAFC as a trigger to spray nitrous starting at a certain rpm.

im trying to use a na ecu to run a turbo motor and i need the afc to get it running at the right a/f... (this is what i have been told...)

I suppose. It's a band-aid. Not a particularly good one. But sure.

is that true? it seams that there is alot of people on here that have them and they work ok...

It's true for the VAF on my MX6, and i was under the impression that one of the things that differs on a VAF vs. a "normal" maf or afm is the voltage readings. And actually, on my MX6, it hits open loop at 75% throttle, so i can only use an AFC for adjustments below 75%. Pretty useless.

If people on here are using them, then go for it.

[Lex]

Don't once you hit 100% wot, these cars go into open loop anyways, making an AFC useless?

This is INCORRECT and this myth has to die.

Open and closed loop refers to a system that has feedback (closed loop) and one that does not have feedback (open loop).

Feedback on combustion A/F ratios is given by the Oxygen sensor. Because it is a narrowband sensor, it does not read rich and lean mixtures accurately. When going WOT, the ECU targets a rich A/F ratio and therefore DOES NOT rely on the O2 sensor to tell it if it has met the A/F target.

This is what open loop means. The ECU is not relying on the O2 sensor.

The VAF and Engine Speed (from the CAS) tell the ECU under how much load (from the VAF) and at what speed the engine is operating. The ECU has a lookup table with load on one axis and RPM on another which indicates for how long the injectors should open.

If the engine is in a cruise or idle mode, this injector opening time is trimmed (or adjusted) by the O2 sensor reading meaning it is in closed loop so that it meets ~14.7 AFR.

If the engine is at WOT, it makes use of the load signal and the RPM signal to determine how long the injectors should be open but does not trim the value according to the O2 sensor since the sensor is not accurate when the ECU is targeting rich mixtures as aforementioned.

So the VAF is used AT ALL TIMES while the vehicle is operating.

The SAFC is used to fool the ECU into thinking there is less or more load on the motor than there actually is so that the ECU targets more or less fuel by scaling the VAF signal coming into the ECU.

This is however NOT recommended because the ECU also targets ignition timing advance based on the same VAF (load) and RPM readings.

So let's say you add larger injectors. Since the ECU is programmed for smaller ones, in order to run appropriately you have to fool the ECU into thinking it sees LESS load. Fine. You get your desired AF ratio.

But what happens to timing? First of all, using an NA ECU is not appropriate on a turbo application since the timing is FAR too advanced. Secondly, now you are fooling the ECU into thinking there is less load on the motor than there actually is. So that means the ECU will target even more advanced timing.

The most effective way properly calibrate a vehicle is to either get a proper ECU designed for a turbocharger or go with a standalone.

Also note that the B6T has vacuum advance on the timing so I am not entirely sure if the ignition control is done via the ECU or not.

[concealer404]

(Placeholder, i'll have my thoughts in here in about 30 minutes)


Alright, PLEASE correct me if i'm wrong when this is all applied to these engines, but i'll readily admit that i'm not 100% positive that it does. But this is what i KNOW about the system on my MX6, and being that they're both VAF based, i maybe have dumbly assumed that it was the same.

On the MX6 (vaf):

An SAFC modifies the VAF voltages sent to the computer, making it think that more or less air is coming in than it would normally read.

When open loop is acheived, all sensors are actually ignored, so any effect that an AFC would have would be completely negated. Now, being that on my car, open loop is hit at 75% throttle, that renders an AFC pretty useless.

Isn't there also the issue that an AFC works on a 0-5v scale, and our VAFs read above and beyond that?
I thought i saw somewhere that a VAF operates on a 2-9v scale.

Again, this is based on my research on the F2T, so this may not all apply to the B6 or whatever this guy is running.

[ryan1]

mx-6 vaf/vams are 0-10 volt so the safc will not work.

[concealer404]

Right. Are BP vafs different voltage ranges?

[Lex]

After 1990 a lot become standardized with Mazdas and Fords. Prior to that, everyone did funky things sometimes. The F2T and B6T seem to fall in the funky category while the BP, KL, newer B6 seem to fall into the more standardized OBDI category.

The SAFC works fine on a BP.

In terms of ignoring all sensors - it has to be understood that the control system can't do that simply because it would not be able to determine how much fuel to inject and how to set ignition timing. It can't all of a sudden turn into a carburated car.

[concealer404]

After 1990 a lot become standardized with Mazdas and Fords. Prior to that, everyone did funky things sometimes. The F2T and B6T seem to fall in the funky category while the BP, KL, newer B6 seem to fall into the more standardized OBDI category.

The SAFC works fine on a BP.

In terms of ignoring all sensors - it has to be understood that the control system can't do that simply because it would not be able to determine how much fuel to inject and how to set ignition timing. It can't all of a sudden turn into a carburated car.

Ah gotcha. I'm not sure on the timing for the F2T in that case, but in terms of the fuel, it'll just dump it all, which is why on a stock F2T, people have recorded a/f ratios even richer than 10:1 depending on conditions.

[Lex]

The fact that you say depending on conditions makes me believe it's not just injectors pulsed at 100%. 10:1 is common on stock turbo cars.

[concealer404]

Hrmmm.... i may need to do more research. Here's what i'm basing my thoughts off of. That said, seems none of it applies to the OP, so at this point, i'm going to apologize for de-railing his thread.

http://www.mx6.com/forums/1g-mx6-other-performance/113934-q-about-apexi-afcs.html

http://www.mx6.com/forums/1g-mx6-other-performance/164469-safc-discussion.html

There's a whole host of threads like that.

[Lex]

I think there is a lot of misinformation out there.

Most automotive sensors are regulated to 5V. Regulating to 12V is not ideal since battery voltage can get below that. Same can be said about 10V.

People also confuse what closed loop/open loop means. This refers only to the feedback signal and in this case it is the O2 sensor, not the VAF.