AFR Wideband O2 Readings
March 10th, 2020, 05:32 PM
#1
AFR Wideband O2 Readings
Hi,
Just installed an AFR wideband O2 gauge to monitor the ratios. For my application, things seem to be dialed in where the engine likes it to be and all runs smooth. Timing is set based upon the build, the advance curve in the MSD have been set and the carb runs smooth without any hesitation or issues.
As I'm still learning the AFR levels and the variances, I wanted to share what some basic numbers were showing at idle and in gear (driveway). It started to rain so I didn't get to road test it yet but that will be the next couple of days. When I started the car up and she settled, the idle mixture was reading around 12.5 and the needle stayed in that range give or take a couple hash lines. When I put it into drive, it would move around slowly between 13 and 14. From what I can read up online, these numbers seem to be in the acceptable ranges, am I correct? When I do take a road test, what sort of things should I expect to see and what should I be wary of?
Background engine detail is a rebuilt 350 with forged flat-top pistons .030 over, TH350 automatic, mild cam, Edelbrock intake, Holley 750 and an MSD R2R distributor.
Just installed an AFR wideband O2 gauge to monitor the ratios. For my application, things seem to be dialed in where the engine likes it to be and all runs smooth. Timing is set based upon the build, the advance curve in the MSD have been set and the carb runs smooth without any hesitation or issues.
As I'm still learning the AFR levels and the variances, I wanted to share what some basic numbers were showing at idle and in gear (driveway). It started to rain so I didn't get to road test it yet but that will be the next couple of days. When I started the car up and she settled, the idle mixture was reading around 12.5 and the needle stayed in that range give or take a couple hash lines. When I put it into drive, it would move around slowly between 13 and 14. From what I can read up online, these numbers seem to be in the acceptable ranges, am I correct? When I do take a road test, what sort of things should I expect to see and what should I be wary of?
Background engine detail is a rebuilt 350 with forged flat-top pistons .030 over, TH350 automatic, mild cam, Edelbrock intake, Holley 750 and an MSD R2R distributor.
March 10th, 2020, 06:59 PM
#2
Registered User
Join Date: Nov 2008
Location: Central Fl
Posts: 7,892
Depending on camshaft 13.8-14.0 at idle is normally good.
14.5 or so at cruise, again depending on cam.
12.3-12.5 at WOT.
Remember with today’s E10 gasoline stoich falls about a half point throughout from previous figures.
14.5 or so at cruise, again depending on cam.
12.3-12.5 at WOT.
Remember with today’s E10 gasoline stoich falls about a half point throughout from previous figures.
March 13th, 2020, 08:37 PM
#3
Got to dial in the carb between vacuum gauge and the new wideband AFR gauge. Got the following readings. Side note is that WOT was based on flooring it on fairly empty main roads but no highways.
Park idle - 12.5-12.8
In-gear idle - 13.2-13.5
Light acceleration 30mph - 14.5-15.0
WOT mid range RPM (street) - 12.5-13.0
Vacuum was steady at 16 in park and ~12 in gear. No leaks that I could find and current carb jets and power valve seem to be the right combo. Engine really ran well and seemed to respond well to all the adjustments.
Park idle - 12.5-12.8
In-gear idle - 13.2-13.5
Light acceleration 30mph - 14.5-15.0
WOT mid range RPM (street) - 12.5-13.0
Vacuum was steady at 16 in park and ~12 in gear. No leaks that I could find and current carb jets and power valve seem to be the right combo. Engine really ran well and seemed to respond well to all the adjustments.
March 13th, 2020, 09:34 PM
#4
Registered User
Join Date: Nov 2008
Location: Central Fl
Posts: 7,892
Got to dial in the carb between vacuum gauge and the new wideband AFR gauge. Got the following readings. Side note is that WOT was based on flooring it on fairly empty main roads but no highways.
Park idle - 12.5-12.8 Too rich
In-gear idle - 13.2-13.5 About right but odd that this is leaner than the no load situation
Light acceleration 30mph - 14.5-15.0 Probably ok but a bit lean
WOT mid range RPM (street) - 12.5-13.0 Should be more consistent than a half point spread.
Vacuum was steady at 16 in park and ~12 in gear. No leaks that I could find and current carb jets and power valve seem to be the right combo. Engine really ran well and seemed to respond well to all the adjustments.
Park idle - 12.5-12.8 Too rich
In-gear idle - 13.2-13.5 About right but odd that this is leaner than the no load situation
Light acceleration 30mph - 14.5-15.0 Probably ok but a bit lean
WOT mid range RPM (street) - 12.5-13.0 Should be more consistent than a half point spread.
Vacuum was steady at 16 in park and ~12 in gear. No leaks that I could find and current carb jets and power valve seem to be the right combo. Engine really ran well and seemed to respond well to all the adjustments.
March 14th, 2020, 05:51 AM
#6
Registered User
Join Date: Nov 2008
Location: Central Fl
Posts: 7,892
Wrong carb for your application but OK we’ll try to work with it.
You need to adjust your idle mixture screws a little bit leaner. Then see what your air/fuel is once you put it in gear. From there you may have to play with the idle air bleeds and /or idle circuit as well, and maybe even the high-speed air bleeds for WOT. However unfortunately you will have to drill those yourself, as they’re not adjustable. That’s one of the reasons why I never buy those carburetors. They are more difficult to tune then they need to be. Next time you may want to consider a carburetor with replaceable air bleeds etc.
You need to adjust your idle mixture screws a little bit leaner. Then see what your air/fuel is once you put it in gear. From there you may have to play with the idle air bleeds and /or idle circuit as well, and maybe even the high-speed air bleeds for WOT. However unfortunately you will have to drill those yourself, as they’re not adjustable. That’s one of the reasons why I never buy those carburetors. They are more difficult to tune then they need to be. Next time you may want to consider a carburetor with replaceable air bleeds etc.
Last edited by cutlassefi; March 14th, 2020 at 05:57 AM.
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