Optimum air/fuel ratio?

**SS#1531** · 09-28-2006, 10:43 AM

I think I know the answer to this, but to confirm, what is the optimum air/fuel ratio at WOT?

**SSpdDmon** · 09-28-2006, 12:44 PM

It's not a set standard. My experience has me running between 12.2 and 12.8. You want it a little richer around peak torque and leaned out a little around peak h.p. So, my AFR is set to be 12.5 below peak torque, richen up to 12.2 at peak torque, and lean out to 12.8 at peak h.p.

**SSwt00SS** · 09-28-2006, 01:43 PM

+1 your A/F should not exceed 13, too lean at the point and higher. over a prolonged period of time one risks burning a hole in a piston or blowing a head gasket.

**SS#1531** · 09-28-2006, 03:57 PM

That's about what I thought, thanks

**Sarge** · 09-28-2006, 04:07 PM

Idle or cruising around 2000 rpm 15's
WOT 12's
Aty 75mph on the highway...I'm running 15.2 at 2100 rpm....
WOT I'm running high 11's low 12's.....

**MadSeason** · 09-28-2006, 04:27 PM

Originally Posted by Sarge

Idle or cruising around 2000 rpm 15's
WOT 12's
Aty 75mph on the highway...I'm running 15.2 at 2100 rpm....
WOT I'm running high 11's low 12's.....

thats almost exactly what my car is dialed in at

only difference my idle is a high 14

**Silver Streak** · 09-28-2006, 08:03 PM

Hmm..... just had my car dynoed... and the graph shows a low of 13 and fluctuates up to 13.5ish... Would I need to get it tuned to fix that? How bad is it the way it is? Am I hurting performance?

**SSpdDmon** · 09-29-2006, 04:58 AM

Yeah, you don't want to run that lean. You can get a tune or a MAF translator to adjust your fueling. Long term, running that lean can hurt the motor. Plus, you're not making the most power. If you ever watch an Indy race, the drivers occasionally increase their AFR at points in the race to conserve fuel (those in-car dials are freakin' awesome!). The side effect is, their lap times go up. LS1's are kind of in the same boat. Run them too lean and they don't make as much power as well as become prone to detonation easier.

**Wikid NaSSty** · 09-29-2006, 08:59 AM

I believe O2's should be around 885 mV @ WOT to achieve an A/F ratio of 12.5 to 13.0

**SSpdDmon** · 09-29-2006, 12:30 PM

Originally Posted by Wikid NaSSty

I believe O2's should be around 885 mV @ WOT to achieve an A/F ratio of 12.5 to 13.0

I would high recommend AGAINST using anything the stock O2's say for WOT fueling. They only work within a narrow range around 14.7:1. That's why they're called narrow band oxygen sensors.

Case in point...I've got my car dialed in as stated above and my NBO2 sensor reads ~935mV@12.2 and ~915mV@12.8 the last time I checked. The only thing they're good for is to tell the PCM if it's somewhat rich or lean compared to stoich...

You need a wideband to tune WOT and try not to let anyone tell you otherwise.

**GatorSS** · 09-29-2006, 03:07 PM

You cannot tune for WOT without wideband...I learned that the hard way after trying many times using the stock narrowbands.

**Wikid NaSSty** · 10-03-2006, 08:03 AM

I know the stock o2's arent a good way to tune. However, the way I did it was to lean back WOT with my MAF translator until I saw a little but of knock retard on my scanmaster, and then I dialed it back 2%. With it there I monitor my o2's and they usually range between 880 to 890 mV pretty consistantly. This is a decent baseline o2 voltage that tells me my car is running close to where it should be. You are probably right though.....stock o2 voltages probably vary by car and for a true tune a wide band is a must. I assumed the stock o2's would read close to the same for LS1's.

I know the o2's only give a simple rich/lean signal while driving, but once you hit WOT (or close to it), the o2's stop giving an oscillating voltage and give me very consistant #'s for a basline tune. Someday i'll get a real dyno tune with wideband o2's once my engine is modified enough to make the cost worth it.

**SSpdDmon** · 10-03-2006, 09:25 AM

Originally Posted by Wikid NaSSty

I know the stock o2's arent a good way to tune. However, the way I did it was to lean back WOT with my MAF translator until I saw a little but of knock retard on my scanmaster, and then I dialed it back 2%. With it there I monitor my o2's and they usually range between 880 to 890 mV pretty consistantly. This is a decent baseline o2 voltage that tells me my car is running close to where it should be. You are probably right though.....stock o2 voltages probably vary by car and for a true tune a wide band is a must. I assumed the stock o2's would read close to the same for LS1's.

I know the o2's only give a simple rich/lean signal while driving, but once you hit WOT (or close to it), the o2's stop giving an oscillating voltage and give me very consistant #'s for a basline tune. Someday i'll get a real dyno tune with wideband o2's once my engine is modified enough to make the cost worth it.

Based on the trends I've seen people claim about O2 sensor mV, 890 is on the low/lean side...not to mention the fact that you could actually lean out your AFR beyond 13.5:1 without seeing any knock retard. That's definitely not the way I'd recommend tuning AFR.