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Reset my V-AFC settings....

868 Views 7 Replies 3 Participants Last post by  71dsp
I think it was 71dsp who posted about the e-mail he received about the settings. Although he didn't actually post the settings, I tried what he said.
Before the flames start: I know this is not the safest way to go about this, but whatever.
I had had my fuel settings at -4%, for the low and high cam. I changed those to -2% on the low-cam,0% between 4600 and 5100 and -7% up until redline.
Now I will repeat the sentiments of the post stated above. USE THESE SETTINGS AT YOUR OWN RISK.
BUT, I noticed a much better pull through VTEC, maybe 5-10hp. I plan on checking my plugs in about a week to see if I'm going to lean in VTEC, but from the feel of it, it is tuned much better now.

Regarding the "every car is different" motto; I realize that this is true due to many different variables, BUT I feel that similarly modded Preludes will have similar fuel needs. Now there will surely be slight diffences, but it's not like I'm using fuel settings for a B16 on my H22.

Questions? Comments?
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Why would you lean it out so much during high cam? Is that for both high and low throttle?
Well, in that post I talked about it said that the typical -4% or -5% setting on the low cam turned out to be running a little lean. Then it said that there was a significant power increase in VTEC leaning it out a little more than the -4% or -5% setting.
I hope you realize that the preludes run rich for a reason, cuz running rich is much safer than running if you gonna drop 7% I really hope you know what you're doing.
wait, wouldnt 7% be a little too much to drop down? ESPECIALLY in the extreameties taken place in the engine during vtec. leaning it out all the way to 7% would have a good chance of detonating in high rpms wont it?

all i know is that from my settings (that aol site everyone uses) i didnt feel much difference but in 4th gear. i felt it run alot smoother in forth at like 50 mph. honestly that was the only thing i felt besides the DRAMATIC reduction in feeling the vtec crossover point.

can someone actually explain what happens when u supply more fuel or less fuel besides the terms of runing "rich" or "lean"? i need a technical explanation so i can understand what is really going on in the engine with messing around with fuel with the VAFC.
Ok, here's the way i understand it... 14.7 parts of air to 1 part fuel is what is considered ideal for combustion. Running rich, or by adding more fuel and therefore decreasing the ratio, the combustion is less hot but it's guaranteed to combust. Running lean, or by decreasing the amount of fuel and therefore increasing that ratio, combustion is hotter and if decreased too much may not detonate at the correct time, causing all kinds of internal problems ranging from simple engine knock to a warped crank. Therefore, if your O2 sensor is out of whack, your ECM will always run the motor much richer and retard the ignition timing cuz it doesn't know whether it's running rich or lean, but running richer is always safer...hence, safety mode. Our 5gens are programmed to run rich from the factory, therefore a V-afc is useful in leaning out the mixture to get more power, cuz a leaner, hotter combustion leads to more power.
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<font face="Verdana, Arial" size="2">cuz a leaner, hotter combustion leads to more power.[/B]</font>
hmm thats a pretty nice explanation there. i pretty much knew most of that though, but still clears things up. but now, since hotter combustions gives u more power, how hot is too hot for our ludes? i think thats the one thing everyone with the VAFC is trying to figure out. once we know that point and not to cross it, we can maximize the engines potential
<font face="Verdana, Arial" size="2">Originally posted by smoothludey:
.... cuz a leaner, hotter combustion leads to more power.</font>
Not necessarily. Most cars make the most peak hp at AF ratios of 12.5:1 to 13.5:1. Especailly turbos. Some make the most power at very rich ratios of 11:1 and richer. However, it is true the leaner mixtures will burn hotter, and make more power up to a point. The problem is detonation and engine load. If the only way to remedy a detonation problem with a lean mixture is by retarding the timing, then you lose power. However, if you cool the combustion by adding more fuel (lowering AF ratio), to combat detonation, you can run full timing, and not lose as much power. Then the richer AF will make more power than a leaner AF.

Also stoich is optimal for emissions purposes, not necessarily power.

North Texas Prelude Owners Group
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