Wideband afr value

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johan_89

Member
Joined
May 11, 2021
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Location
Sweden
My Car
Mach 1 - 72 with 460 and c6
Hi!
I'm tuning my edelbrock 750 (1407) with a wideband afr sensor and need help to understand the values I got from it.
Idle 13,4-13,6 afr
Cruise in 50 mph 10,9-11,1 afr
Vot 12,7-13,2 afr
I think it's too rich in cruise speed and a little bit too lean at wot. Too rich at idle to but if I Lean it out it will hesitate when I start from zero.
My calibration is nr 17 in the diagram I attached as a picture. Secondary jets 113".
Don't know if it matters but my camshaft is edelbrock 7167 and the gauge I use is Innovate MTX-L. Mach 1 with 460 and c6.
Thanks in advance😀
 

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I've done quite a bit of carb tuning with a wideband. I put together a data logger that includes left and right wideband AFR, manifold vacuum, RPM, speed, and knock. I have the parts to add TPS and fuel pressure, but .....too many irons in the fire.

Set idle mixture using highest vacuum reading or RPM. If it's an automatic, set that in drive. The AFR you end up with is what your engine likes. Don't try to hit a target, unless you have to for some sort of emissions test.

I record both low speed and high speed cruise AFR values. To do that, you need to know the RPM you're observing AFR at, and the transition RPM where your carb begins to pull from the boosters. LS cruise runs off the idle, aka low speed, circuit. It will have its own AFR that is controlled by the low speed air bleed, idle feed restrictor, and mixture screw adjustment. High speed is, as the name implies, when the engine is primarily pulling through the boosters. High speed air bleed and main jets are the main control knobs here.

The 50mph readings you have are probably transitional....better to be clearly on the LS and clearly on the HS circuits to get definitive data. What is the RPM? High Speed with a 750cfm should put you on HS circuit at about 2500 RPM. I usually record LS cruise at 2000 RPM and HS cruise above 2500 RPM.

For a street car, I am tuning for 15:1 AFR on LS and HS cruise. That requires a fairly lean main jet and the ability to change out your IFR's and possibly, air bleeds. This tuning will uncover any sort of stumble you may have. It is not necessary to tune this lean. You'd be fine at 13:1 and your plugs will look ok or maybe slightly rich.

For wide open throttle (WOT), the main jets, PVCR's (power valve channel restrictors) and the PV, itself determine the AFR under those conditions. Engines from our era tend to like 12.5-13:1 AFR. It's better to be too rich than lean. I find that a moderate street cam, giving 12" vac idling at 750 will like an 8.5 power valve. That enriches the mains sooner. than a 6.5 or any lower, for that matter.

Start with tuning for the LS and HS cruise numbers you're after. The HS cruise will establish your main jet. With that, you can tune for WOT and alter the PVCR jet to get to the 12.5-13 number.

In summary, your idle is probably lean...mine likes 12-13...about like WOT.

Your 50MPH is very rich and depending on RPM is either a main jet (HS cruise, or a IFR, LS cruise) that needs to change.

Your WOT numbers look pretty good...they are safe but you won't know how to improve w/o some sort of performance device or drag strip. I use a device call Dragy for my comparisons. It's a lot of fun to see how your changes impact the performance....highly recommended but wish it had a way to download.

If you made it this far, congratulations! If I can be of further help, feel free to ask.


Edit: Shoot, I just saw that you're running an Edelbrock carb....all my inputs are for a Holley. The circuits will control the AFR in a similar manner, but I'm not familiar with Edelbrock carbs so I can't tell you how the holley circuits cross over to the Edelbrock.
 
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Great read, especially as I consider a wide band gauge. Question, what’s a PVCR? I’ve been monkeying around with my Holley 750 and haven’t discovered this yet.
PVCR stands for power valve channel restrictor. When the metering block uses a power valve, that jet, in combination with the main jet and high speed air bleed, meters fuel through the boosters, aka main, aka high speed circuit. PVCR's are the two small holes under the power valve. They will be fixed-diameter on entry-level carbs. Buy a tunable metering block if you decide to venture down that rabbit hole.
 
Great explanation, the more i tinker the deeper that rabbit hole gets…….. thanks!

Seems some of the simple things make the biggest difference. For example I had an initial stumble on aggressive acceleration…. After adjusting and changing most other items on the carb I swapped to a different accelerator pump cam(on throttle linkage) and VOILA ….. stumble GONE!

The learning curve is steep!
 
OP's running an edelbrock carb. He's running what I would call rich and he's at calibration 17, which is at the extreme rich corner of the chart.

I would say lean it out according to the chart. I would try calibration 14 or 4. And then to get rid of the lean condition right off the line, move the little pin to the "make it run richer" hole here. You just pull out the tiny cotter pin, move the linkage to the next hole, and push the cotter pin back in.
1718812081925.png
 
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I've done quite a bit of carb tuning with a wideband. I put together a data logger that includes left and right wideband AFR, manifold vacuum, RPM, speed, and knock. I have the parts to add TPS and fuel pressure, but .....too many irons in the fire.

Set idle mixture using highest vacuum reading or RPM. If it's an automatic, set that in drive. The AFR you end up with is what your engine likes. Don't try to hit a target, unless you have to for some sort of emissions test.

I record both low speed and high speed cruise AFR values. To do that, you need to know the RPM you're observing AFR at, and the transition RPM where your carb begins to pull from the boosters. LS cruise runs off the idle, aka low speed, circuit. It will have its own AFR that is controlled by the low speed air bleed, idle feed restrictor, and mixture screw adjustment. High speed is, as the name implies, when the engine is primarily pulling through the boosters. High speed air bleed and main jets are the main control knobs here.

The 50mph readings you have are probably transitional....better to be clearly on the LS and clearly on the HS circuits to get definitive data. What is the RPM? High Speed with a 750cfm should put you on HS circuit at about 2500 RPM. I usually record LS cruise at 2000 RPM and HS cruise above 2500 RPM.

For a street car, I am tuning for 15:1 AFR on LS and HS cruise. That requires a fairly lean main jet and the ability to change out your IFR's and possibly, air bleeds. This tuning will uncover any sort of stumble you may have. It is not necessary to tune this lean. You'd be fine at 13:1 and your plugs will look ok or maybe slightly rich.

For wide open throttle (WOT), the main jets, PVCR's (power valve channel restrictors) and the PV, itself determine the AFR under those conditions. Engines from our era tend to like 12.5-13:1 AFR. It's better to be too rich than lean. I find that a moderate street cam, giving 12" vac idling at 750 will like an 8.5 power valve. That enriches the mains sooner. than a 6.5 or any lower, for that matter.

Start with tuning for the LS and HS cruise numbers you're after. The HS cruise will establish your main jet. With that, you can tune for WOT and alter the PVCR jet to get to the 12.5-13 number.

In summary, your idle is probably lean...mine likes 12-13...about like WOT.

Your 50MPH is very rich and depending on RPM is either a main jet (HS cruise, or a IFR, LS cruise) that needs to change.

Your WOT numbers look pretty good...they are safe but you won't know how to improve w/o some sort of performance device or drag strip. I use a device call Dragy for my comparisons. It's a lot of fun to see how your changes impact the performance....highly recommended but wish it had a way to download.

If you made it this far, congratulations! If I can be of further help, feel free to ask.


Edit: Shoot, I just saw that you're running an Edelbrock carb....all my inputs are for a Holley. The circuits will control the AFR in a similar manner, but I'm not familiar with Edelbrock carbs so I can't tell you how the holley circuits cross over to the Edelbrock.
It should work in similar way with an edelbrock than a holley, I gues the biggest difference is the metering rods.
I had a holley 850 dp before and a friend helped me tune it and the car runs good but took way to much fuel (3,6 litre/ 10km, think it's 6,5mpg) in 50 mph economy cruise and the spark plug were almost great, maybe a little lean. So I changed to edelbrock and now the car runs great but now I can se with my wideband gauge it's to rich in cruise so ofcourse I want it to be more economic. Now It take 2,39 litre/ 10 km, 9,84 mpg I think.

In 50 mph I have about 2000rpm so it should run at LS. How much is my idle AFR affect in 50mph and 2000rpm? I wanted to try nr 4 or 14 in the edelbrock tuning sheet but I hadn't those metering rods in my tuning set from edelbrock. So I tried with the rod nr 10 in the sheet 73x47, so it should run leaner both at wot and cruise in 50mph, just tried ones at wot and it goes leaner but in cruise it was no change. It feels like there are something I don't understand🤔 By the way my rear end ratio is 2:75.
 
OP's running an edelbrock carb. He's running what I would call rich and he's at calibration 17, which is at the extreme rich corner of the chart.

I would say lean it out according to the chart. I would try calibration 14 or 4. And then to get rid of the lean condition right off the line, move the little pin to the "make it run richer" hole here. You just pull out the tiny cotter pin, move the linkage to the next hole, and push the cotter pin back in.
View attachment 89896
I already have it in the top hole. I turned the idle mixing screws 1/4 turn richer and the hesitation disappeared. But I can't get it leaner at cruise speed (se my latest post) I have also tried smaller primary main jets 113" and the 73x47 metering rod and it still runs at about 11.9-12,5 AFR in light steady cruise in 50mph. How long do I have to drive to test? I just try for about 1,5 km.
 
What step up springs are you running, and verify that the step up pistons move freely in their bores with no binding. Have you tired connecting a vacuum gauge to check what your vacuum is while driving at cruise?
 
What step up springs are you running, and verify that the step up pistons move freely in their bores with no binding. Have you tired connecting a vacuum gauge to check what your vacuum is while driving at cruise?
I had the orange 5" but now I tried the yellow 4" but no difference. No I haven't tried to connect the vacum gauge while driving, good idea. I have to get a longer hose for the gauge before I can try.
 
I already have it in the top hole. I turned the idle mixing screws 1/4 turn richer and the hesitation disappeared. But I can't get it leaner at cruise speed (se my latest post) I have also tried smaller primary main jets 113" and the 73x47 metering rod and it still runs at about 11.9-12,5 AFR in light steady cruise in 50mph. How long do I have to drive to test? I just try for about 1,5 km.
What I was suggesting was put it in the bottom hole, not the top one. Putting it in the bottom hole should make it pump more fuel right when you give it some beans. That would allow you to change the spring and rod away from the most extreme rich corner of the calibration chart, which would lean it out at cruise.
 
What I was suggesting was put it in the bottom hole, not the top one. Putting it in the bottom hole should make it pump more fuel right when you give it some beans. That would allow you to change the spring and rod away from the most extreme rich corner of the calibration chart, which would lean it out at cruise.
I looked at it and it gives more fuel it the top hole and least in the bottom hole. The top hole allows the pump to make a deeper pump and then gives more fuel.
 
I tried in my desperation with a smaller jet 110 and 73x47 metering rod and it made a leaner AFR up to 43mph and 1700rpm but over 1700rpm and 50mph it goes richer again. I think my carb runs in HS circuit over 1700 rpm. What can I do now, smaller jets on the secondary? But it should affect the wot AFR also?
 
On a holley, you should be able to tune the LS and HS cruise AFR without the secondaries coming into play. You can count on that being true on a vacuum secondary, but you may begin to crack them open on a double pumper. For WOT AFR, I will disable the secondaries so that I know I'm only tuning the primaries. Once you get the AFR you want (secondaries disabled) use the area of main and power valve jets to calculate the area of secondary jets. When the secondaries are disabled, the primaries will run about 1/2 point richer (varies with engine combo) because the signal to the boosters is stronger. When the secondaries come into play, the contribution from the primaries will naturally lean out a little. I would imagine you can replicate that process with an Edelbrock, but I can't tell you how to do it.

Earlier, you asked about the contribution of mixtures screws to the LS cruise AFR. It's a small amount...I've been able to move it as much as 1/2 a point, but it's really more of a fine tuning....and the priority should be on getting the max vacuum/RPM at idle in gear, rather than a knob for cruise AFR. Don't get too wrapped up in dialing in perfect numbers....these will change depending on ambient conditions, engine temperature, etc....that's the beauty of closed loop control with fuel injection.

I suggest you also consider your ignition timing curve and how your vacuum advance is set up. Ignition timing has a big impact on the engine's response...especially at lower RPM.
 
Hi!
I'm tuning my edelbrock 750 (1407) with a wideband afr sensor and need help to understand the values I got from it.
Idle 13,4-13,6 afr
Cruise in 50 mph 10,9-11,1 afr
Vot 12,7-13,2 afr
I think it's too rich in cruise speed and a little bit too lean at wot. Too rich at idle to but if I Lean it out it will hesitate when I start from zero.
My calibration is nr 17 in the diagram I attached as a picture. Secondary jets 113".
Don't know if it matters but my camshaft is edelbrock 7167 and the gauge I use is Innovate MTX-L. Mach 1 with 460 and c6.
Thanks in advance😀
WITHOUT knowing what fuel you are running the numbers have no meaning...

https://www.motortrend. com/articles/wideband-oxygen-sensor/

Screenshot 2024-06-22 at 5.54.50 PM.png
 

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Then the chart gives you your target A/F numbers.

Screenshot 2024-06-23 at 11.56.08 AM.png
Idle and cruising 14.7
Part throttle 13.21
Wide open throttle 12.5

Running a carb is not as precise turning for A/F as is Fuel injection. So
Idle / cruise I would target 14.2-14.5
part throttle stay below 13.2
full throttle 12.5 is enough

Once you can get it jetted/dialed in those ranges your can then play a little up/down in the throttle/rpm ranges to see what your motor likes... each engine is different . also, can play with total timing too

MORE Fuel is not a good thing

jm2c
 
Then the chart gives you your target A/F numbers.

View attachment 90018
Idle and cruising 14.7
Part throttle 13.21
Wide open throttle 12.5

Running a carb is not as precise turning for A/F as is Fuel injection. So
Idle / cruise I would target 14.2-14.5
part throttle stay below 13.2
full throttle 12.5 is enough

Once you can get it jetted/dialed in those ranges your can then play a little up/down in the throttle/rpm ranges to see what your motor likes... each engine is different . also, can play with total timing too

MORE Fuel is not a good thing

jm2c
I have tried nr 4 in the tuning chart and I got AFR 11,8-12,2 in 50mph. Should I try with smaller primary jets? How much under stock jets can I go? I have the biggest (119) on the secundary to keep wot AFR.
 
Sorry, johan-89, I have no experience with Edelbrock carbs ...
Tuning is a lot of prior experience / knowledge and a little trial and error... because each engine is different.

edit: "How much under stock jets can I go?" you have an AFR meter... just keep going smaller and watch the meter.
"I have the biggest (119) on the secondaries to keep wot AFR." you have manual secondaries ... primaries & secondaries should be same or very close ...

 
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