Subaru Impreza GC8 & RS Forum & Community banner

Apexi S-AFC or HKS S-AFR?

3139 Views 12 Replies 7 Participants Last post by  cRayZee
I posted this in i-club and didn't get much response.. So, i'll try here

All right guys this is for those of you with experience with either of these products. Which one would you recommend I should get? I've only seen the S-AFC's on other cars, no S-AFR's yet. Is this becuase the AFC's cheaper? Besides the price, what's the advantage of one over the other?

Also, another thing that came up was I heard this rumor that the SAFC was useless on MAP cars. How did this rumor start? Why does the SAFC (not?) work on MAP cars?


1 - 13 of 13 Posts
what year is your car? it is debateable whether they work on 2000+ models.
MY01 RS-- I just did a search on i-club and a lot of talk about the ECU relearning or the SAFC not being in effect until WOT. Well, i mean, that makes sense. You don't really need extra power when you''re doin some light driving.

Just worried that if i buy an SAFC or the HKS unit that it won't be a waste of money. Also, I don't know if either of these products would be good for F/I. I heard you don't really need either of these..just an rrfpr?? hmm.. should i have posted this thread in the FI forum? :)

I am Using the HKS unit

I am using the HKS unit. I think it's a great product with one main disadvantage, more people are using the Apexi unit so recieving assistance is easier. But I think the fact that it works with the MAF makes it better along with the fact that it's easy to use.
i'm leaning towards the HKS unit, cuz my friend could get me $100 off retail:cool: What i'm interested in is from what i've read in similar threads is that the AFC works but only at high throttle positions, which is fine with me.. which is IMO the only spot where it only really needs to work.

Also, I'm planning on boosting my car. So, with a MAP sensor, I'd have to use a zener diode to block out the boost signal to the ECU. So, with this, will the AFC really be useless once the it sees boost?

What advantages will an AFC/RRFPR have over the other once i have boost? What other options are there for engine/fuel management for force induced MAP-based cars that aren't too expensive?

why not get a voltage clamp? instead of the diode?
cRayZee said:

Also, I'm planning on boosting my car. So, with a MAP sensor, I'd have to use a zener diode to block out the boost signal to the ECU. So, with this, will the AFC really be useless once the it sees boost?

yes. i'm pretty sure fooling the ECU and then trying to alter the fuel maps will not work.
so, which one is better?

I really was interested in the HKS unit. similar price and would probably work good. here's some info I had saved from a long time ago. enjoy:)

-HKS AFR (Air Fuel Ratio Regulator)
The AFR is designed for lightly tuned vehicles (intake, exhaust) to allow for mild adjustments in the a/f mixtures through sensors. The AFR allows up to 1 A/R point; rich or lean, for the best possible power gains.

HKS AFR is a simple fuel adjusting device that adjusts the Air/Fuel ratio by changing the airflow voltage output to the vehicles factory stock computer. The AFR was designed for vehicles that are lightly tuned (air filter, exhaust system, etc.) and that need only slight fuel adjustment. The 10 setting adjustment indicator allows the user to richen or lean the stock settings by approximately 0.2 of an A/R point. Both the lean side and rich side have five notches. This enables the user to search for the best possible set up for your vehicle! The D-Type and L-Type are the two types of AFR available.

hope this helps.
See less See more
here's somethin i posted on i-club..

I think the safc is a little too flashy and fancy-looking for my taste...

OK..So, lets say I get turbo, use a zener diode to limit the max signal the ECU sees from the MAP sensor. Correct me if i'm wrong, but the safc is tapped between the MAP and ECU so the safc can modify this signal to let the ECU think it needs to richen/lean out the A/F ratio, right? so, with boost, this signal is already at maximum, so the SAFC can't modify the signal anymore than what it has at max. But it can lean out the mixture, is that correct? so, what other methods would I need to do to richen the mixture?

WRC, that for the regular AFRs. Here's what HKS says about the Super AFR:

The HKS Super AFR is the very first airflow meter correctional device in the industry with a built in CPU. The advantage of having a built in CPU is that instead of making corrections to the airflow meter voltage/map sensor, the characteristics of the airflow meter/map sensor is inputted in the CPU so it can calculate the most accurate amount of air flow. Since the correction will be made to this specific intake volume, the correction ratio of fuel will be precise and proportionally correct. With an illuminated digital display and face mounted adjustment controls, the compact Super AFR is a simple to use fuel computer that offers many of the advanced features that were once exclusive to full engine management systems. The L.E.D screen is utilized to digitally display all adjustments as they are entered along with RPM and fuel % adjustment (over baseline) in real time. The Super AFR is compatible with virtually any fuel-injected vehicle, 12Volt, 2-12 cylinder vehicle that utilizes a hot wire, Karmen Vortex, airflow meter or pressure sensor. The internal CPU allows it to be versatile and utilized on many of the newer type airflow meters.

The air/fuel Ratio Correction function of Super AFR allows complete fuel curve tuning by offering eleven points between 650 and 8000 RPM of adjustment, that can be arbitrarily moved in 50 RPM increments. Each point of adjustment offers a tuning range of 50% rich to 50% lean of the factory baseline setting in 1% increments. Also incorporated in the Super AFR is the Idle Correction function, where Idle fuel mixture can be adjusted from 50% rich to 50% lean of the factory baseline setting in 1% increments within the idle range of 650-1500 RPM. This offers the ability to adjust idle air/fuel ratios as modification progress and require further specific levels of tuning to compensate for the characteristics of high lift cams and/or larger injectors. The response function, similar to the one in the VPC, allows for adjustments to the fuel settings upon throttle inputs to improve driveability and performance. Much like the corrections made to the idle mixture to compensate for high-lift cams and/or larger injections, the response function can also compensate for differences in fuel requirements upon initial throttle input as airflow characteristics are changed from high-lift cams, larger injectors, and bigger turbos. In detail, the response function allows for management of engine response in milliseconds with six points of air meter signal adjustment between 650 and 5000 RPM that can be randomly moved in 50-RPM increments. Additionally, an Electronic Idle Stabilizer function (EIDS) function, which buffers the dramatic airflow meter signal fluctuations, prevents the engine stalling or stumbling effect associated with the sudden imbalances in the air/fuel ratio of airflow meter-equipped vehicles that utilize discharge blow-off valves that vent to the atmosphere.

It sounds good, but I wonder about this and ECU learning. It has been said that the ECU (2000+) will learn and override the corrections that the S-AFC except at WOT. If the S-AFR is constantly adjusting (learning the ECU?) and the ECU is learning the S-AFR, which will win?
See less See more
A fellow on i-club has his MY2000 dyno'd with a S-AFC to prove everyone that it did work. And it did work. He saw improvements in horsepower and torque. The only problem with the test was that he SHOULD have gone back two weeks later and seen if his S-AFC had been corrected by the ECu, or if it was still throwing more fuel into the cylinders. The S-AFC does work at WOT.

Yea, i've read that link. It doesn't really matter if the ECU does correct the changes during regular driving. What matters is when you're at WOT and want that extra power. If it does work, then i'm cool with that, since the ECU ignores the O2 sensor and just adjusts A/F ratio according to what it's programmed to do.
1 - 13 of 13 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.