Some questions:

Can you not rely on narrow band o2 at all in WOT?

If it's showing .900 mV at 100 kPa WOT, then doesnt that mean you're a little on the rich side still?

Besides reading plugs and track testing, how can you best rough in the WOT tune with only using the narrow band o2?

How do you rough in the PE table with only feedback from narrow band o2?

Are there any other tables than PE that should or need to be modified (WOT)?

 

You can shoot for 700mv to 950mv. It's far from acurate AND has no useable relation to actual a/f ratio. BUT if you don't have a wb then I guess something is better than nothing. Besides, edelbrock makes an a/f gauge from a nb o2. So I would think it would be at least good to verify the changes/make sure you are adding or subtracting fuel.

 

I have an autometer AFR guage (for narrow band o2). It's under the X-mas tree as we speak, along with the 2 pod A-pillar. So in a couple weeks, it will be installed.


Isn't 700mV on the lean side?

Is there a particular mV reading that's close to what a 12.5 : 1 actual AFR would be ?

I heard that .875 would be "close" to an actual 12.5 :1 - 13 : 1 AFR, is that false?

 

Can you get close? Yes.
Will it be perfect? No.

Whatever you do, do NOT shoot for any one given millivolt reading somebody tells you. I know people will disagree, but this is how I feel and every single car & sensor is going to be somewhat different. This is especially true with aftermarket exhausts and positions of O2 sensors.

With my corvette I put together a chart showing Wideband O2 and Narrowband O2 readings from the same dyno pull. I divided the narrowband millvolts by 100 to make the curve more visible on the wideband chart.

Going by this chart with my own car I shoot for around 930mv at WOT.



If you are going to do this sort of thing I highly recommend you do the same and get your car on a dyno w/Wideband capability so that you can cross-referencce your narrowband readings to see what your particular car likes.

 

700mv can mean anything. Just ask 305sbc. I had a topic about the nb for wot tuning... It is impossible to devise an a/f ratio chart using a narrowband o2.

 

I have a 3 wire heated o2 located right behind the collector of my driverside Longtube header.

It appears to me from your chart that 875 mv is close to a 13 : 1 AFR !


Looks kinda promising?

 

Like I said....., I would not use my chart for use on your car. It could be, but I would not trust it until being able to prove it with a wideband reading to cross-reference. I don't want to be the reason somebody melts a piston.

 

It's ok, I have forged pistons! j/k

Well, I think I'm gonna shoot for .900 + for now to be on the safe side. Anything else I should take into consideration until I get this thing on the wideband?

 

I agree with that statement. I don't think the narrowband is useless. In fact, I have a narrowband lighted A/F Gauge in my A-Pillar pod. It is very helpful for quick ideas on where the fuel mixture is. I have found it particularly useful when I didn't have my laptop hooked up and just kept an eye on what was going on. No matter what, it will tell you if you are rich or lean. Shooting for 900+ will definitely keep you on the safe side of things (IMHO). Just don't try to use it too much for acceleration enrichment stuff because it just doesn't seem to be responsive enough. This is the same approach that I took before having access to a wideband. I'd shoot for 900+ and then take it to the dyno and lean it out using their wideband.

Tim

 

Cool, then I'm on the right track!

I dont want to even get into Accel Enrichment (pump shot, right?) until I finish VE and PE.

Is this an ok route to go about things? Or, should accel enrichment be tuned first before PE?

 

It's totally Ok. That's how I started too!

Tim

 

Seems like the common facts are that little o2 mv changes can result in big actual A/F changes.

I'd go for 900mv, or even 850... give or take. Just don't drop below 850, lean is lack of power.

Saw a post on here somewhere, dyno pull the guy was 10:1 A/F..... and when he tuned it to 12.7ish he only gained like 20hp.
But if you were lean by 2.7 points, you'd gain WAY more than 20hp going towards ideal.


So it's much better to be over rich (aslong as you don't foul the plugs).....

 

I agree, I'm going to try for 900mV for now until I can get her on a wide-band.

I will need help with PE though, when I get to that point. Getting closer!

When I was under the car last night, I noticed a crack in my tranny x-member!!

I need to get that fixed before I make ANY more WOT passes !