My O2s are reading 980 on both banks all through WOT. I think that 890- 900 millivolts is where they should be. What determines the fuel mixture at WOT? Is it the MAF? I have heard that hte O2s dont effect the WOT mixture. I hate running this rich, please help.

 

At WOT the car is in open loop and does not use the O2 sensors. Is your car running rich or lean at patial trottle? There are some tables that the car uses to get the A/F ratio at WOT. Tell me witch way your car is running and we can go from there. I won't be back on the board until 9 o'clock EST tonigt(Putting Nitrous in today) but I will help you than.

 

You can adjust the fuel at WOT with the PE table (Power Enrichment). If you have a stock fuel map, you will notice that it calls for quite a bit of fuel at around 5,000 rpm ... better safe than sorry.

When you are adjusting the PE table, you should be on a dyno with a wide band O2 sensor, it will get you better results than by going off the MilliVolts from your cars O2 sensors.

On the wide band, I believe for a normally aspirated car you should be shooting for a 12.8 to 1 A/F ratio ... thats just a vague recollection ... anyone else??

Hope this helps

LWM

 

Yeah, I kept lowering my A/F ratio at the track, making a pass logging with Freescan, and then saw that my O2s didn't change a bit. I kept doing that and finally gave up/got scared...

 

LWM,

I like your assessment of the 12.8 ratio and I understand from all my other readings that that is in line.

However, I was around 12.6 (looking at PE vs temp and PE vs RPM tables). When I moved it to about 12.2, I actually got 20 HP from that move. I think that from all my reading that this is too rich in PE mode. However, my DataMaster Dyno is really helpful and I find it to be accurate on a comparison basis from one run to another.

LWM, anyone...is 12.2 a bit rich? If so, why am I making more power?

Ben

 

Take the 20 hp and call it a day ...

In my case ... I saw an increase of 50 HP going from an AF ratio of 10.4:1 to and AF of 11.4:1 ... that's where I called it quits ... I don't see any gain in buying a new engine before I want to. ...

The boys at the shop were wanting me to go to a smaller ring ... leaner mixture ... but ... I didn't feel lucky ...

So ... is 12.2 a bit rich ... yes perhaps, but not overly so, you may have avoided some preignition with the richer mixture ... and dyno runs can and do vary a few percentage points.

Did the computer take out any timing?

All I can say is keep the AF ratio in the 12's and that is "good enough for government work"

Hope this helps

LWM

 

I've heard that 13:1 is what you want to shoot for most of the time but that LT1's seem to make the most power at a safe 12.2-12.3 to 1 A/F ratios.
Anyone have any other opinions?

 

my experience w/ two modded LT1's. first was a heads, cam exhaust ect motor. going from 11.7:1 to 12.5:1 (wideband on a dyno) jumped RWHP from 323 to 347. no gains by going leaner. FYI...the factory O2's at WOT read 920 to 930mv before and after the dyno tune(Auto Tap scanner). with my current bored and stroked LT1 we went from 14.2:1 (yah, a little lean) to 12.6:1. rwhp went from 380 to 405. 13.1:1 got us 400 rwhp. factory O2's at WOT were the same 930mv before and after the dyno tune!!

 

How do you add or subtract fuel with LT1 edit?

 

As has been said, you cannot use lambda (factory type) O2 sensors to fine tune your AF ratio.

In terms of the optimum AF ratio most NA cars do best somewhere in the 13.0-13.5 range. The exact number depends on the specific combo. Depending on the test conditions (density altitude) you may want to be on the rich side of optimum to give a safety margin. If the density altitude is low (low temp, high barometric pressure, low humidity) when you test the AF will go leaner when the density altitiude is higher (hotter, more humid, lower barometric pressure).

At the dyno shop where I help out with tuning we usually start at ~12.5:1 for supercharged cars. Same cautions apply but more so: a little rich costs just a few hp, a little lean can break parts.

Rich Krause