Please correct me if any of below is wrong...because this doesn't make sense to me:

-the stock ECU always try to maintain 14.7 A/F ratio in open loop mode (non-WOT)
-most people with VAFC say they use it to lean out the stock air/fuel mixture. I also heard most N/A application should shoot for ~13 A/F ratio.

This confuse me....isn't 13 A/F ratio is RICHER than 14.7? How comes they say they are trying to leaning it out.

I'm thinking about getting a VAFC because my carsound cat got destroy only after one track event. Apparently my cat is soaked by fuel
So i think i need a VAFC to lean it out....but this 13 A/F ratio confuses me...

 

Usually people lean out the low end, or low throttle settings, that will help you maintain better gas milage while your not flooring it.

Also, people put them on chipped ecu's that are usually way to agressive for what most people are running. Those tend to run really rich in the low rpm range, once again leaning it out helps.

 

This is an excerpt from a message I left on a mailing list a while back. It may shed some light here:

"OBD2 is not THAT bad. It actually makes thing much easier to work on if you have the right tools. As to the ECU resetting itself when you turn off the car, this is incorrect. What it boils down to is short term and long term fuel trim and how the computer is compensating. This applies to OBD1 AND OBD2. Have you ever noticed that once you do mods that the rear of the car is covered with soot. Seems contradictory to everyone telling you that intake and exhaust mods leaning the car out. Actually, both sides are right. When you do mods, the car is actually leaned out but. When driving around in closed loop mode, the computer will look at the short term fuel trim and notice that it is lean and will "ratchet" the long term fuel trim up. If it still sees lean on the short term trim, it will ratchet the long term fuel trim until it (STFT) is where it is supposed to be. This computer can correct the fuel trim up to about 25% more air flow. After this, it cannot correct. What you end up with is correction of the low-throttle and engine-speeds by the factory ECU.
Now the trick part. What the computer learns in low-throttle and engine-speeds from LTFT it uses to modify the tables for Wide Open Throttle (Open-loop) even though the computer is not actually compensating as it was in Closed loop mode. Since the computer has been seeing lean-lean-lean, it modifies the tables for a rich mixture. The problem is that the WOT tables are already rich so there car ends up too rich. That explains the lean and rich syptoms that both sides describe.
Typically the mods that you do will lean the car out (make more power) but the computer will compensate for it within a half hour of driving. Something like a Apexi Super AFC works great for this. Use the AFC to trim the WOT settings only and let the ECU take care of the low-throttle and engine-speed settings. You can look at a dyno graph that has the effects on air-fuel ratio by resetting the ecu. Not much power difference but look at how much the ratio changes http://www.lightningmotorsports.com/images/ecureset.jpg Remember this happens in BOTH OBD1 AND OBD2...."

 

I am really puzzled right now.......

I have a 95 ex, I/H/E, bought a VAFC because I REALLY wanted to have it, but anyway, I got it tuned.....

I strapped my car onto the dynojet, and started tweaking......to my fuc%$ˇ$ surprise, the car got 3 more WHP giving it MORE FUEL!!! We richened the mixture by 3 points on the low lobe, 2 points on the vtec lobe...

AND, on a cold cold night, doing some side by side draggin´, I could spank my friend even harder giving it +5 on the VTEC lobe....

I am puzzled, since I also thought what you said.......I´ve read it everywhere....
But I think the dynojet aint lying, cutting the fuel reduced power by 3 whp, period....it was 100% consistent.....

 

You are indeed correct !! That is why there is no "correct" or baseline settings to "get your car close". Every engine has it's own fuel needs which need to be adressed on a case by case basis. If you notice my previous post, I said "typically the mods will lean the car out and make more power" but as you have found, it is not always necessarily the case. One thing I have found on the Hondas while tuning is that the lean A/F ratio will not necessarily make more power. From the graph in the previous post, the A/F ratio changed by 1 full point but the HP was almost identical. Cool huh?


[Modified by lightning, 6:19 AM 5/29/2002]