apexi S-AFC II, good or bad?

Smeltej25 · Post by **Smeltej25** » February 21, 2004

ive heard a lot about the apexi s-afcII but all the stuff that im hearing is all bad about it, so ill ask you guys if you know a lot about it at all

but basically what i need to know is what exactly does it do(specific)?
and if it is bad for your car or not, just so i can clear up some confusion about what it is and does and if it is bad or not!

reason i was so concerned is because i have been looking into going the forced induction route, and i was curious about that specific part!

Post by **kotomile** » February 22, 2004

What it does is lies to your ECU to get it to make power. I don't see why it would be any worse than any other "AFC hack" out there, what specifically are they saying about it?

Does AEM make a plug-n-play for the Subarus?

esmith13 · Post by **esmith13** » February 22, 2004

I have an AFC II as art of my turbo kit. It works excellent for my needs.

Basically what it does is intercept the ECU's fuel map settings and adjust them by way of adding or subtracting a percentage of what the ECU planned on doing.

Example:

Lets say at a particular throttle/RPM position the ECU wants to inject 300cc's of fuel. But in the case of a N/A car you wan to use the AFC to lean out the fuel a little to get more HP. So ou set the AFC at that rpm/throttle position to -10%. Now the ECu thinks 300cc's were injected but the truth of the matter is only 270cc were injected since the AFC removed 10% of the fuel.
With a turbo you usually work in the opposite direction by adding extra fuel for boosting. Also especially with a turbo you may have put in larger injectors. so when the ECu thinks it said to inject 300cc's (if you had 300cc injectors) your now really injecting 550cc's of fuel with your new 550cc injectors. (most honda's use pulse injectors. They squirt their full capacity of fuel ALL THE TIME, and the ECU just determines how often that is necessary). So in this case you need to back out a percentage of fuel to compensate for using larger injectors.

The AFC itself is not as complex as the ECU's fuel map tho. Where the ECU can hold map data for any specific throttle/RPM setting, an AFC holds fuel settings for RPM ranges on two maps, one for Hi throttle and one for Lo Throttle. Being less percise in that way makes it not as efficient overall as the ECU, but since it is just a piggyback to adjust the ECU's fuel map it works as good as you need it to.

Most people with a completely stock car gain 15-20WHP using a AFC and dyno tuning their car to optimize it's settings.

Most of the bad reviews you heard were probably idiots who tuned it themselves on the fly without a dyno and went too far, or they were scared and didn't lean it out enough to make a difference.

In the end you either have to dyno tune with a wideband O2 sensor or get an A/F guage so you can do it yourself safely. Do that and you'll be VERY happy with a S-AFC II. Just make sure you get the model II. It has the ability to set fuel curves up in smaller increments so you can do more fine of a tune with it.

Oh, and i can't think of another product that does the same thing that is better than a S-AFC II. Unless you count a hondata or similar chip/flash - since leaning out fuel is the first half of what these chips/flashes do.

good luck with your choice.

Eric

esmith13 · Post by **esmith13** » February 22, 2004

Damn, i just realized how much I just typed... sorry it was soooo long.

Eric

Post by **BRYCE** » February 22, 2004

Ha that helped out alot. I was always fuzzy about that. Let me get this striaght in a N/A engine you want to lean out the fuel, so less fuel. and in a turbo charged car you want to increase the fuel for the extra air . I got it

Post by **BRYCE** » February 22, 2004

And whats the difference between S-AFC and the V-AFC the Vtec Air Flow Comp?? Is it just that it compensates for vtec too. and is this necisary for a engine with vtec??

esmith13 · Post by **esmith13** » February 22, 2004

The V-AFC can adjust VTEC engagement and I beieve also adjust fuel in the same way as the AFC PLUS being able to compensate for VTEC too.

It is not necessary to buy a V-AFC if you have VTEC. That's why I don't need a V-AFC II for my Si. i would recommend the S-AFC II over the V-AFC. If you can get a V-AFC II that's different tho. The model II's have more adjustment points and a larger adjustment range than the model I's did. I also think if the fuel map is more important to you than changing VTEC engagement, you should get the S-AFC II instead because it's got more fuel related options than the V-AFC does. The "S" stands for "Super" so something about the fuel maps MUST be better than in the V-AFC version.

Let us know how your decision goes

Eric