AFR

[JMo60]

I just got my wideband installed, and was wondering if any of the experienced 3x00 tuners have any input on a perfect WOT AFR? im pullin around 13.2 at WOT, i know this is close, but i was wondering if anyone has input on this??

my only tuning capability is an AFPR, so its pretty crude at best

[SappySE107]

It differs from car to car slightly. I would richen it up a tad. 12.5-12.9 NA. With nitrous, you will probably want closer to 11.9-12.5 (guessing). Without a dyno to compare results on, all you can do is ballpark it for safety.

[sprucegagt]

/\ Agreed. Starting off N/A in the 12.5 range is a good start. But to get it in the sweet spot you need a dyno.

[Superdave]

13.2 is ok.. a tad lean but isn't going to hurt anything, I keep mine around a 12.7-13.2 range (it bounces around at WOT).

[Alxsmt]

what happened to the 14.7 being perfect?

[SappySE107]

Not for performance. You don't want a constant AF ratio for all conditions.

[Alxsmt]

oh, hmm good to know

[IsaacHayes]

14.7 for cruising, but when WOT you richen it up a bit. Looking back through a log of my car, the commanded AFR or Target AFR (what the computer hopes to achieve) is 14.7 until you go WOT, then it goes 12.7 13.1, 13.3, 13.4, 13.5 and hovers around there, then when it finally hits the upper RPM's, it goes to 12.8, 12.1, 11.8, 11.3, and 11.2 until the up shift, which it returns to the 13's. One log where I was seeing some really high RPM's and hit the rev limiter before the trans could shift, it even hit 10.5 as commanded fuel ratio.

Anyone know why it's like that? I take it that perhaps it's a safety thing, that higher RPMs they richen it up just to prevent running lean at really high RPMs from the factory??? Also I do know that it will calculate what your WOT fueling should be based on the BLMs, but does not adjust while you are WOT. I have seen a boost in WOT power from a new O2 sensor, which proves that.

Like spruce said, there is a sweet spot. Sometimes leaning it out a bit will make more power, but you always will be richer than 14.7 when WOT.

[JMo60]

thanks guys, i think i will richen it up a tad, and see how that works out.. maybe when i get some time, ill do some datalogging and try tuning it right

[Monzsta]

I got less knock and was able to run a bit more timing in the 11.8 range. The car felt stronger then when I was running 12.5 and less spark. Maybe it's how I have my combustion chambers worked.

[sprucegagt]

I got less knock and was able to run a bit more timing in the 11.8 range. The car felt stronger then when I was running 12.5 and less spark. Maybe it's how I have my combustion chambers worked.

That's way too low for a N/A application. I'm sure you'll find more power on a dyno by leaning out the mixture and readjusting the timing curve. Is that measurement with a wideband or just the commanded AFR?

[Superdave]

That's way too low for a N/A application. I'm sure you'll find more power on a dyno by leaning out the mixture and readjusting the timing curve. Is that measurement with a wideband or just the commanded AFR?

X2...

You don't need alot of timing on these heads, back it down to 25 degrees or so... then get the AFR's in order..


After all that, if you feel the need just bump up the timing a degree at a time while watching for knock and unstable AFR's (too much timing will do funky things to them).

[Monzsta]

That's way too low for a N/A application. I'm sure you'll find more power on a dyno by leaning out the mixture and readjusting the timing curve. Is that measurement with a wideband or just the commanded AFR?

It's with a wideband. I'm throwing out my old tune anyway and starting fresh with a Venture .bin instead of the Lumina's old 3100 bin.

[lampy]

Running richer at WOT helps keep the combustion temps lower and reduce the chance of pinging.

[Monzsta]

Well, the Venture bin works great... except now the fuel gauge doesn't work. LOL!! Guess I'll have to make a hybrid bin.