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illinipo 09-25-2009 04:01 PM

"safe" afr for high compression NA...
After 6 months of PRP ownership with mechanical issue after mechanical issue, my tune is FINALLY in the correct zip code. Now begins the lengthy and fun process of fine tuning. Im so happy to finally say, "im gonna go tune [:)]" instead of, "I HAVE to go tune [mad]"

Part of that fine-tuning is AFR. I dont have a dyno in my garage (I dont even have a garage) so I can't play around with things to find out what makes best torque. Nor am I concerned with the absolute best torque... its my only car and i'd rather be safe. That said, I believe I have some torque to gain from where i'm at.

I know afr and spark are always doing a waltz when it comes to detonation. Less fuel heats things up, and more spark increases cylinder pressure, both of these things can cause detonation. I recently spent a few hours finishing up the .8-1.0 load cells of the BKT using my method of listening for pinging (it works!), and they are still way under MBT. This is at .867 lambda or about 12.74:1. Datalogs are within .01-.02 lambda of that so the MTF is good.

Here is the question:

Would it be better to lean it out a bit to say .875 (12.86:1) or .882 (12.96:1) and lower the spark a bit? This is a 10.5:1 zetec and I often see IAT's over 100, would it be okay to even go over 13 due to the heat? (I would think no...)

Or, should I keep it at .867 and the borderline spark I just tuned to? Is there any torque to gain from where I'm at?

03OrangeSVT 09-25-2009 08:23 PM

I would richen it up if it were mine... about 12.5 or so, but thats just me.

illinipo 09-25-2009 08:27 PM

alrighty, thanks.

Before I had the MTF tuned it was running around 12.3-12.4 and there was a very noticable butt dyno gain when I tuned it to 12.8.

But maybe if I brought it down to 12.5 I could bring the timing closer to MBT.

1turbofocus 09-25-2009 10:01 PM

I would shoot for the 12.8 to 12.9 , for NA safe for playing around , If your going to the track I would shoot for 12.6 to 12.7 as you will see it creep up to 12.9 to 13 with long hard pulls , that with 95-100 octane will make for a safe weekend

I have told you many times to send me your file or datalogs and I would help but nothing

You have a 2002 ZX3 , why not use the stock knock sensor vs messing with the noise


illinipo 09-26-2009 03:35 AM

the sensor is going nuts. it is just giving jibberish. all of the log files I have sent you in the past showed it going crazy, anything above .4 load it will go full retard no matter what spark. You helped me out in the beginning figuring out what was wrong with it, and we ended up just turning it off... Since then ive been doing alright with the tuning, just some mechanical issues that I needed to work out. Had to go to SVT injectors, had to vent the PCV, still need the right size buckets, etc etc. its not even worth tuning it right now really, everything's gonna change when i get some bigger buckets. I have about .010" to gain on almost all valves... the cam timing and overlap being that far off is making things interesting.

Thanks for the tips on afr.

1turbofocus 09-26-2009 08:15 AM

I can set the sensitivity of the KS in my software on each Cyl this seems to bring it back in line with the few ZX3 that are off


illinipo 09-29-2009 06:56 PM

I ended up going to .882=12.96, had to pull .5 degree in some places a full degree in others, but the car pulls a million times better.

iminhell 09-30-2009 03:12 PM

Just a guess but, might you be tuning rich due to too much timing and thereby loosing power?

illinipo 09-30-2009 03:23 PM

I assure you my timing is not too high. It is dissapointingly low... I'm not even close to MBT.

Also that is not a Zetec by any means so what he says about AFR does not necessarily apply.

But what you are asking is the essence of my question:

What makes more torque, is it more timing and more fuel, or is it less timing and less fuel?

My butt dyno says the latter is true, and I only had to pull a tad bit of timing to add .2 afr without knock.

iminhell 09-30-2009 04:57 PM

If the later is true, then one would have to assume that the knock sensor is hindering you. More timing, to a point, should yield more power. That also assumes the AFR is correct.

Honestly though, you'll never know unless you put it on the rollers.

I think I'm running more compression than you and I've just got a off the shelf chip, and I'm pretty sure I'm not experiencing any knock (though I've no way to substantiate that).

Out of curiosity, did you have to gap your plugs down too?
I have to run a .040" or smaller gap or I seem to blow out spark, maybe it's knock though; .045" and I feel it for sure. BTW, I seem to be getting by fine on pump 92.

Also remember that with more pressure comes more heat. Not sure what you're running for plugs, but I'm having good luck with the NGK LZTR5A-13 / 4998 gaped @ .035".

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