AFR Readings

[Moparfiend]

Hi, I have a simple question regarding AFR curve vs RPM’s. Does AFR typically read 5-7 points high (leaner) at idle than at cruise or acceleration?
If my AFR is accurate and it may not be especially at idle I am reading 22 at Idle and 14.5 under acceleration or cruise ie higher rpms.
I don’t know what normal or typical is. I am using an Innovate WBO2 sensor with the tail pipe clamp from them.

 

[Kern Dog]

Whoa!
22 is W A Y too lean!
I followed the target numbers that I read online but my car went slower....So I changed a few things and here are my results:
The target was mid 14s at idle and cruise, 12 to 12.5 at WOT.
I can get the number for idle but I'm still in the 13s at cruise and high 11s to mid 12s at WOT.
No black smoke, no rich "Smell".
I am not certain but I suspect that ethanol gasoline may need to run a bit richer than straight gasoline to make the same power.

 

[Moparfiend]

Whoa!
22 is W A Y too lean!
I followed the target numbers that I read online but my car went slower....So I changed a few things and here are my results:
The target was mid 14s at idle and cruise, 12 to 12.5 at WOT.
I can get the number for idle but I'm still in the 13s at cruise and high 11s to mid 12s at WOT.
No black smoke, no rich "Smell".
I am not certain but I suspect that ethanol gasoline may need to run a bit richer than straight gasoline to make the same power.

Thanks KD. Whats your set up look like? Your picking off AF mix just after the header via bung? What AF sensor you using?

 

[Kern Dog]

I have an AEM that reads from a O2 sensor in the right header collector.
440 based 493, 10 to 1 compression, Mopar 528 solid cam, 1.6 rockers, 2" headers, Edelbrock Performer RPM intake, MP electronic ignition, Barry Grant Speed Demon 850 Vacuum secondary with electric choke. #83 primary jets, #90 secondary.

 

[Moparfiend]

I have an AEM that reads from a O2 sensor in the right header collector.
440 based 493, 10 to 1 compression, Mopar 528 solid cam, 1.6 rockers, 2" headers, Edelbrock Performer RPM intake, MP electronic ignition, Barry Grant Speed Demon 850 Vacuum secondary with electric choke. #83 primary jets, #90 secondary.

View attachment 918912

Nice! Solid roller or solid flat tappet? What heads?

 

[71RRHI]

I agree 20:1 is way to lean. I have a 512 stroker, large solid lifter cam, aluminum heads, and 2" headers, FI Tech throttle body injection. On O2 sensor installed just aft the collector on passenger side. Runs 14.1:1 at idle, about 12:1 at WOT.

 

[Kern Dog]

Nice! Solid roller or solid flat tappet? What heads?

Solid flat tappet with Howards EDM lifters....they squirt oil through the lifter to the cam lobes for reduced risk of wear.
Edelbrock heads, 84 ccs milled to approx 82 ccs, ported.
The car idles nice. Not too racy but enough to sound pretty good, at least to me.

 

[33 IMP]

I read a piece by Jeff Smith (car craft tech ed.) where he said that the o2 readings at idle cannot be trusted. Because of reversion and large overlap, the confusion of idle mixture (radical camshaft sound) the idle readings can be all over the place. I wouldn't necessarily assume it is dead lean. What kind of readings do you get under light load just off idle, after the idle smooths out?

 

[andyf]

Hi, I have a simple question regarding AFR curve vs RPM’s. Does AFR typically read 5-7 points high (leaner) at idle than at cruise or acceleration?
If my AFR is accurate and it may not be especially at idle I am reading 22 at Idle and 14.5 under acceleration or cruise ie higher rpms.
I don’t know what normal or typical is. I am using an Innovate WBO2 sensor with the tail pipe clamp from them.

Your readings are not correct. The engine won't run at 22:1 so that reading isn't possible. My guess is that your tail pipe clamp setup doesn't actually work. You'll need to have a bung welded into the head pipe before you can get accurate readings. Make sure that there are no exhaust leaks in the system or else you'll get false lean readings.

 

[Moparfiend]

I read my plugs and they look good. Andyf thats what someone else has said that idle may not be accurate. I have to build a new exhaust system still so putting a bung in for now is not worth it. I guess I will retune the AF mix just using a vacuum gauge for now.....

 

[HEMI-ITIS]

Your readings are not correct. The engine won't run at 22:1 so that reading isn't possible. My guess is that your tail pipe clamp setup doesn't actually work. You'll need to have a bung welded into the head pipe before you can get accurate readings. Make sure that there are no exhaust leaks in the system or else you'll get false lean readings.

Yes,,,,,,,,,SUM-TING-WONG!!!

 

[wyrmrider]

as andy f said 22 is impossible
you have a leak somewhere
edit
I've never see 20+ even with stratisfied charge motors

 

[RJRENTON]

IMO...
Are the o2 sensors controlling anything or just reporting a reading. To be accurate, should there be two lambda sensors (o2 sensors), one in each collector OR exit pipe immediately down stream of exhaust manifolds. Most, if not, all o2 sensors are heated electrically, so they are sampling at a minimum temperature. IF you are sampling on just one exhaust pipe or using unheated sensors, is the accuracy of the A/F ratio an accurate representation of the exhaust gas?
If just one cylinder misfires, or does not completely combust, will this yield an inaccurate reading? If the A/F reading device does not control the mixture, small changes in road load (vacuum or manifold absolute pressure) or engine RPM or speed can make large changes in readings. I would think that spark plug coloration or individual cylinder exhaust gas temperature readings would be more infomative. Just my opinion of course.
BOB RENTON

 

[Moparfiend]

IMO...
Are the o2 sensors controlling anything or just reporting a reading. To be accurate, should there be two lambda sensors (o2 sensors), one in each collector OR exit pipe immediately down stream of exhaust manifolds. Most, if not, all o2 sensors are heated electrically, so they are sampling at a minimum temperature. IF you are sampling on just one exhaust pipe or using unheated sensors, is the accuracy of the A/F ratio an accurate representation of the exhaust gas?
If just one cylinder misfires, or does not completely combust, will this yield an inaccurate reading? If the A/F reading device does not control the mixture, small changes in road load (vacuum or manifold absolute pressure) or engine RPM or speed can make large changes in readings. I would think that spark plug coloration or individual cylinder exhaust gas temperature readings would be more infomative. Just my opinion of course.
BOB RENTON

I believe the O2 sensor is electrically heated as you can see it warm up in the data. I agree the more sensors the more accurate I am not an expert but others maybe here. this is the one I have and it addresses what you asked:
https://www.innovatemotorsports.com/products/lc1.php

 

[andyf]

I read my plugs and they look good. Andyf thats what someone else has said that idle may not be accurate. I have to build a new exhaust system still so putting a bung in for now is not worth it. I guess I will retune the AF mix just using a vacuum gauge for now.....

You should put the wide band where you want it now so you can sort out all of the wiring and mounting issues. If you don't have the ability to weld a bung in place then buy a clamp on bung like this one: https://www.summitracing.com/parts/...MI8-bG_MOH6AIVxR6tBh2cfwQFEAQYASABEgK51vD_BwE

 

[RJRENTON]

I believe the O2 sensor is electrically heated as you can see it warm up in the data. I agree the more sensors the more accurate I am not an expert but others maybe here. this is the one I have and it addresses what you asked:
https://www.innovatemotorsports.com/products/lc1.php

I was curious as to how the equipment worked. Unless one has a fuel injection system, I'm not sure how beneficial it would be with a carburetor system unless it would be similar to the GMs electronically conttolled Quadrajet, where the power piston controlling the primary step up rods (and A/F mixture) were commanded up/down in response to the down stream o2 sensor signal against a preprogrammed data point in a "speed density" algorithm in the engine control's computer. Today's systems use the mass flow method of measuring air entering the engine, usually in terms of grams per second, for accuracy, modified by air temperature (both air and coolant), manifold absolute pressure, throttle position, RPM, MPH, and pulse width controlled individual injectors and overall spark advance and cam position sensors (for advancing/retarding the cam's position in relation to the crankshaft).
To pick an A/F ratio operating point with a non conttolled carb would be almost impossible and trying to repeat that point .....just too many variables. Sure, it might nice to know the number...but to what end? Perhaps, spark plug coloration or the elapsed time trial slips or the tried and true "seat of the pants" determination may be best? Just my opinion of course.
BOB RENTON

 

[andyf]

Knowing the AFR is beneficial if you know how to adjust the carb. You look at the reading on the screen and then you adjust the carb. It isn't as effective as EFI where the computer makes adjustments as you drive, but it works. It is better than looking at the plugs and trying to figure out what to do.

 

[RJRENTON]

Knowing the AFR is beneficial if you know how to adjust the carb. You look at the reading on the screen and then you adjust the carb. It isn't as effective as EFI where the computer makes adjustments as you drive, but it works. It is better than looking at the plugs and trying to figure out what to do.

I've been adjusting, re-adjusting carbs for many years and are well aware of he how-tos. My point was the relative A/F ratio is transitory or like trying to hit a moving point. One A/F reading at a given operating point would be difficult to duplicate. Whereas spark plug readings and/or timing slips are an average of the effectiveness and repeatability of A/F ratios, along eith other timing variables. The other possibilities are dyno runs where HP, torque, RPMs, along with individual cylinder exhaust gas temperatures combined with o2 sensor readings can be measured and optimized, where parameters can measured and repeated, to acieve the "best" operating point. Again, just my opinion of course.
BOB RENTON

 

[andyf]

When you have an AFR reading then you tune the carb circuit by circuit. Start with idle and work your way to power. Idle is the most critical and is fairly simple to do with the car at a warm idle with the choke off and the throttle blades in the correct position (transition slots square). If the idle mixture screws won't get the AFR in the right spot then you have to change the IFR which gets more involved.
Setting the main circuit is usually a little more involved. You have to drive the car on the freeway at cruise and note the AFR and then change the jets when you get back to the shop. Adjusting the power circuit is the most difficult since you need to have the engine at WOT. A chassis dyno is the safest method but it can also be done at the track. Carb has to be opened up to get to the PVCR. This all assumes a Holley carb. A carb with metering rods provides more tuning options.

 

[threewood]

I read my plugs and they look good. Andyf thats what someone else has said that idle may not be accurate. I have to build a new exhaust system still so putting a bung in for now is not worth it. I guess I will retune the AF mix just using a vacuum gauge for now.....

I would ignore the o2 readings and do what you said, tune by vacuum gauge and tach plus how the plugs look. When you get a bung welded in then you can use it with the vacuum gauge.

I'm running a AEM / Bosch o2 in the pass collector. At idle I am around 13.4 to 14.0. It idles nice. Any more or less it wasn't as good. Hughes STL 3842 solid lifter cam, headers, 800 cfm Edelbrock AVS2 carb. WOT is 12.3, cruise is up around 14.0 to 14.5.