Hokay people,

You are the proud new owner (or the confused long time owner) of an APEX’i VAFC, SAFC, or some variation thereof. You may have questions: What does it do? Will it give me m/-\d TyT3 horsepower y0? How do I get my A/F correction just right? Can I set my vtec at 2500 rpms? Hopefully this thread will have some answers. I’m gonna lay down what I’ve picked up from reading manuals, talking to APEX’i and with some experienced, legitimate tuners. Hopefully we can build a base of knowledge here. Please feel free to add comments, discuss points, and correct me where I’m wrong. It’s just that I’ve seen a lot of threads about the units, and it would seem wise to get some kind of reference going.

Installation:
Before you start posting questions that have already been answered, READ YOUR MANUAL. It tells you how to install the unit, how to initialize (set it up) it, and how you can use it to tune your engine. If you can’t figure any of this out, then take it to a shop and have them do it or explain it or both. If you set your unit up incorrectly, you’ll just be mucking up your entire engine.

What does it do?
An AFC (whether it’s S- or V-) can do several things for your engine. It’s a piggyback fuel management system that allows you to manipulate your A/F ratio and vtec engage. I think with S-AFC you can actually save two separate setups in the unit. Say, one for track day (for those of you running c16 or something), and one for around town driving. The reason it’s called a piggyback FMS is because it can really only manipulate what your ECU is already capable of doing. Whereas a standalone FMS runs off of it’s own software, these people have laptops riding bitch, and can do on the spot tuning from their puters.

Will it give me m/-\d TyT3 horsepower y0?
It short: Nope. I’ve seen it free up maybe 10 or 12 horsies or some hard-tuned engines, but the unit is more importantly meant to optimize your current engine, and provide precise regulation. Whether you’re a drag strip driver or a road course driver, you know that power means nothing if your engine is operating incorrectly. The AFC helps you set your ECU to agree with the aftermarket components on your engine, so that your engine can do its best work when you need it to.

How do I get my A/F correction right?
Dyno, dyno, dyno. If you know someone who has the EXACT same model, engine, and mods as you do, you STILL can’t set your AFC up like theirs and expect it to be 100% optimal for your engine. Everyone’s engine runs differently, and once you add mods, you change the characteristics of that engine. Get it up on a dyno and get an A/F readout. You want to produce an A/F ratio that isn’t lean anywhere, or dumping fuel where it needn’t. This is where intelligent tuners come into play.
If you’re only running basic mods (I/H/E) then A/F correction (and the unit as a whole) will do you no real good. If you plan on (or already have) mods like turbo, S/C, or even an aggressive nitrous setup (75+), you’re should really think about some kind of FMS. Running lean will bring your V8 eating days to an abrupt stop.

Can I set my vtec at 2500 rpms?
Yes, you can set your vtec at 500 rpms if you want. For all intents and purposes though, the engine dorks at Honda did a fine job of getting the vtec engage just right. Don’t know how vtec works? Keep reading. Already know how vtec works? Skip the next little bit

Vtec is a variable valve timing setup. Which basically means that a vtec engine has two sets of cam lobes on each shaft. One is a little short, allowing for good fuel efficiency. It’s big brother, the longer cam lobe, is for putting down more horsies at the top end of your tach, but doesn’t really do much for conserving fuel. If this longer cam were to kick in too early, it would have the same effect as any aggressive cam would at low rpm. The idle would be rough, the exhaust would sound a little meaner, and it would probably not give you much low-end power. The vtec cam lobe was meant to run like a deer at 5800 (or whatever your factory engage is) and over.

Sliding the vtec point up or down a few rpms can free up a few horsies. Like I said before, every engine is different, so the stock settings could be off a little. But changing the vtec by more than 800 or so rpms either way is not going to be beneficial.

Well, that’s all I got. Hopefully it’ll help answer some of the introductory AFC questions. Like I said at the top, lets try and keep this a way to build a knowledge base. I don't know everything about these units, but I'm sure there are many drivers on this board that know as much or more than I do. I just wanted to make a thread that would help people understand the basics and get them on thier feet.

 

 

Thank you

 

VTEC won't even engage until it gets sufficient oil pressure, which doesn't occur until upwards of 3000rpm, at which point it may still be weak, causing it to not fully engage properly and create other problems. So for those who misinterpret what was said about the larger cam profile to mean that you can have a rough idle and deeper exhaust sound, realize that it's only in theory...it can't actually work. The info is correct, I just felt the need to elaborate.

 

Optimal VTEC setting for my engine was 5000 RPM, anything less and I lost power.

 

Thanks for clarifying that nolimits.

 

Um that comment about bringing in high cam early isnt really correct.

For starters my apexi vafc goes down only until 4300rpm ie:lowest vtec engagement point...ie:...u cant be idle in highcam...its not possible.

second lowering the vtec AND changing a/f ratios WILL increase HP..this is a fact but the gains are dependant on yer existing mods and its best to get the dyno done professionally (pref with a wide band o2 ) to make sure u dun run it too lean.

3rd if your running yer V-afc with another piggyback unit OR a chipped ecu ie: more aggressive fuel mappings this will ALSO increase power but u may have to change your springs to compensate.

point is that the VAFC DOES increase HP....but few tuners know how to tune it proper, also most tuners charge by the hour so its a costly exercise spending 3 hours on the dyno just to net a couple extra HP. So far ive had my car dynoed 5 times and i was happy on the 5th attempt.

Im currently hitting vtec at 4400 and lean out linearly till -14 at 8000 rpm.

I DO NOT RECCOMEND TUNING YOURSELF save the $$$ and go to a distinguished tuner.

cyaz