Help with WOT fuel mixture
10-08-2002, 11:16 PM
#1
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Thread Starter
Join Date: Feb 2000
Location: Houston,Tx. US
Posts: 15
Help with WOT fuel mixture
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.
10-09-2002, 09:04 AM
#2
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Join Date: Oct 2001
Location: Stationed at Camp Lejeune, N.C. (But Going Home SOON!)- From New Jersey
Posts: 154
Open Loop
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.
10-09-2002, 09:28 AM
#3
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Join Date: Dec 1969
Location: Calgary, Alberta, Canada
Posts: 324
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
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
10-09-2002, 03:03 PM
#4
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Join Date: Jun 2001
Location: Columbus, Ohio
Posts: 295
Originally posted by LWM
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.
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.
10-13-2002, 07:05 PM
#5
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Join Date: Jul 2002
Location: Phoenix, AZ
Posts: 1,277
Originally posted by LWM
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
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
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
10-13-2002, 11:13 PM
#6
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Join Date: Dec 1969
Location: Calgary, Alberta, Canada
Posts: 324
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
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
10-14-2002, 08:57 AM
#8
Registered User
Join Date: Dec 1969
Location: indlps,in
Posts: 41
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!! 
Last edited by carl97ss; 10-15-2002 at 07:55 AM.
10-15-2002, 11:11 AM
#10
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Join Date: Dec 1969
Location: Buffalo, New York
Posts: 10,745
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
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
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