Why does the A/F ratio @ WOT table zig-zag?

I dont have it in front of me at the moment but its rich above "0" around idle then dives below "0" above idle, then its rich, above "0" untill about 4k then dives again for the remainder.
I'm just not sure what the idea is here, as I thought you would want a constant ~12.7-13:1 ratio. Both the stock table and my mail order look this way, also this change (around 4k showed up in my A/F at the dyno, but the car did make good power.

Not exactly sure what you're asking...
The % change vs rpm table could vary as you indicate...but I wouldn't think that would be right. Of the cars I've done on the dyno I've never had a table bounce back and forth/up and down. I've always been adding fuel as rpm increased in order to get the desired a/f ratio that I wanted.

Here's a stock '95 table

rpm / %change

400 4.7
800 4.7
1200 -0.8
1600 -0.8
2000 0.8
2400 0.8
2800 3.1
3200 0.0
3600 1.6
4000 0.8
4400 2.3
4800 8.6
5200 9.8
5600 6.6
6000 2.7
6400 2.7
6800 2.7

See what I mean, up,down, up, dn.
If closed loop is runing 14.7:1 why does it ever dive below zero?

Originally posted by quicksilver97ta
I dont have it in front of me at the moment but its rich above "0" around idle then dives below "0" above idle, then its rich, above "0" untill about 4k then dives again for the remainder.
I'm just not sure what the idea is here, as I thought you would want a constant ~12.7-13:1 ratio. Both the stock table and my mail order look this way, also this change (around 4k showed up in my A/F at the dyno, but the car did make good power.

I've seen this happening on dynos. The operator had to rescale the graph for it to look nice and clean.

Originally posted by quicksilver97ta
See what I mean, up,down, up, dn.
If closed loop is runing 14.7:1 why does it ever dive below zero?

There is another table factored in, the vs. Coolant table. That is already adding an amount to the baseline of 14.7:1, and then is modified by this RPM table.

As for why it would still change up and down, I've wondered this too.

My table (not stock) takes a dive at 4k rpm from 5.1 to -6.3 at 5.6k rpm. This changed my a/f readings from a steady ~12.0:1 to a steady ~12.5:1 Not much of a change, but I guess percentage wise it seems right.
But why change at all? Does an engine make more power leaning out as rpms climb?

Originally posted by quicksilver97ta
My table (not stock) takes a dive at 4k rpm from 5.1 to -6.3 at 5.6k rpm. This changed my a/f readings from a steady ~12.0:1 to a steady ~12.5:1 Not much of a change, but I guess percentage wise it seems right.
But why change at all? Does an engine make more power leaning out as rpms climb?

I have personally seen my dyno numbers change from an AFR of 12.8 to 13.3 in the upper RPM range (3500+) to get a bit more HP. This seems to confirm what others have stated on this board. Since I saw only 3 HP or so increase, I would not lean out in the upper RPM. Denotation for me is a problem in this area and I don't want to risk that.

Currently I run 12.2 AFR.

Ben

Ben, Is it a fairly steady 12.2 or is that at your peak hp?

Originally posted by quicksilver97ta
Ben, Is it a fairly steady 12.2 or is that at your peak hp?

Hmm forced me to take a look at my dyno runs again.

My AFR is consistent in the upper RPM (3400 RPM +) range at WOT and does not vary by more than 0.1. I dynoed at 12.8 AFR and then after reprogramming, the next run I dynoed again at 13.3 AFR. I made more torque across the board with the 13.3 AFR. I use 12.2 to eliminate knock, however I am planning on putting a set of colder plugs in and will redyno in late Sept or Oct and see where I can get the best HP with different AFR's.

Hope this helps.

Ben

Originally posted by 95Blackhawk
Hope this helps.

Ben

It does.