Air Fuel Ratio, E10, Oxygen sensor

[Nate S]

I'm interested in tweaking my A/F ratio to get it "maybe better" and I'd like input from those who have taken different approaches. My starting point is a 426W, 9.25:1 compression, magnum cam, CH4B intake, manifolds, and a 3310 "-0", the one with the Chevy part number. Everything in the carb is stock, 2 power valves, 72's in front, 76's in back. Timing is quick and all-in is 38°. Right now the car runs well with a very mild "unevenness" when going on dead flats or slightly down hill ~ 45 mph. Plugs are very clean, maybe too clean. Stuff the throttle and it's smooth. 0-60 is about 6 seconds.

I intentionally richened up the idle mixture and that unevenness decreased so it appears that it's a bit lean. Actual optimum idle mixture gets the unevenness driving.

So... gut feel says the E10 gas I get locally should warrant a couple jet sizes. The old Mopar tuning guide shows a wildly rich 3310 which I simply don't believe. I'm not going to get to the drag strip so multi-runs with jet changes isn't in my future. I'm considering a wideband Oxygen sensor to have a closer look. I'd probably use it for a couple weeks and take it back off. I'm curious about experiences the group here has had with those sensors. Find anything interesting when you put it on? Was it helpful? I could just bump the jets a couple but that doesn't really answer much, might smooth out the unevenness but is it optimized?

Also worth noting that I actually drive this car. ~100 miles a week. All around drivability is key but I don't want to be giving anything up when I step on it.

 

[67plysat]

I installed an Autometer wideband gauge to dial in an Edelbrock carb, it was more than helpful. I was going take it out after tuning the carb but left it in because it really is interesting to watch. Most interesting is I can see the carb transition between circuits. Also can see the difference between E10 and non-ethanol gas, and also see differences from ambient temp.

 

[68Moparmaniac]

It'll make tuning more scientific than the seat of your pants plug reading etc... this will give you hard data to work with, 13.5:1 to 14:1 A/F would be the sweet spot

 

[6872n73]

I had a similar setup on a 440, ran good but my plugs were always black if i checked after idle and nice tan after running down the road. installed an A/F meter I was able to really get A/F number to what really ran well and take a lot of guesswork out of it.

What helped me the most was off idle and transition.

Once you know your A/F, you'll never go back.

 

[RJRENTON]

IMO...
Air / Fuel ratios are nice to know but they are an instantaneous value, that changes, with air density and temperature AND the type of fuel used, throttle position, engine RPMs, etc. Suppose, you are driving down the road, looked at your A/F instrument and it read 12.5....is this good or bad?....answer...maybe. can you, the driver, duplicate this or any other value consistently? The other aspect is, IF you, the driver, decides this value is incorrect, what do you do....pull off the road and rejet the carb?.

Your carb of choice is the origional Holley 3310 from GM. The carb was "tuned" on a GM dyno for a 396 (402)/375 HP engine. Its no wonder that you have had to adjust the idle and off idle fuel transition circuits for your application, as that GM application used a fairly radical cam and high compression pistons, requiring "different" idle air bleeds, idle feed metering values and likely the position and dimensions of the off idle transition slots, all of which affect the mixture ratios from closed thru WOT positions. PVCR along with the PV's opening point also effect the overall A/F ratios, as long as the manifold vacuum is higher than the PV's opening point. Rather than basing your decision to adjust the A/F ratio on a single data point (meter reading), read the spark plug color as an AVERAGE of the engine's fuel ratios, realizing that spark advance characteristics also effect plug coloration.
Additionally, bear in mind that the fuel's composition absolutely effects the mixture as ETHANOL has half the energy value as gasoline and running a higher percentage of Ethanol will require more (richer) fuel mixture to compensate based on the percentage of ethanol in the blend.
Typically, EFI systems can adjust the A/F ratios in real time by increasing the injector on time (pulse width modulated) and measuring the down stream effect (O2 sensors) and adjusting accordingly to a programmed value (speed density or mass flow).
Using A/F ratios with a carburetor based system seems superfluous as any "adjustments" will be after the fact and impossible to exactly repeat measured conditions, to see IF the the "changes" made, fixed the origional issue, so what's the point of the exercise? Just my opinion of course.
BOB RENTON

 

[Nate S]

Looking like I'll go with the sensor...

Bob, it's worth noting here that we know it's a carburetor and we know how EFI works. We also know the original engine, intended fuel etc, that's why it is remarkably good on the current engine (E10 aside). The hook is the size, accuracy and speed of the feedback loop for jet adjustment. The "look at the plugs" feedback loop is quite slow and somewhat imprecise, it also averages many things that can be adjusted individually. The "look at the ET" is impractical and really only captures WOT. The sensor can give a window into steady cruise, idle, WOT and transition points. If it's flopping around wildly it also shows that. Seems like the accounts from those using this approach lend credence to it being a consistent, accurate way to get feedback.

Question part 2: Does this sound like the right general approach?

• With idle mix set properly run through a variety of low-medium load driving conditions. Identify transition from idle to primary jets. Adjust jets for ~14.0 - 14.7 in those conditions (readjusting idle as needed).
  
• Block secondaries and drill PVCR (if necessary) to get ~12.8 average under WOT, look for abnormalities.
  
• Un-block secondaries knowing the primaries are correct and adjust jets to get ~12.8 at WOT?

 

[RJRENTON]

Looking like I'll go with the sensor...

Bob, it's worth noting here that we know it's a carburetor and we know how EFI works. We also know the original engine, intended fuel etc, that's why it is remarkably good on the current engine (E10 aside). The hook is the size, accuracy and speed of the feedback loop for jet adjustment. The "look at the plugs" feedback loop is quite slow and somewhat imprecise, it also averages many things that can be adjusted individually. The "look at the ET" is impractical and really only captures WOT. The sensor can give a window into steady cruise, idle, WOT and transition points. If it's flopping around wildly it also shows that. Seems like the accounts from those using this approach lend credence to it being a consistent, accurate way to get feedback.

Question part 2: Does this sound like the right general approach?

• With idle mix set properly run through a variety of low-medium load driving conditions. Identify transition from idle to primary jets. Adjust jets for ~14.0 - 14.7 in those conditions (readjusting idle as needed).
  
• Block secondaries and drill PVCR (if necessary) to get ~12.8 average under WOT, look for abnormalities.
  
• Un-block secondaries knowing the primaries are correct and adjust jets to get ~12.8 at WOT?

Question: If you can insure the EXACT same conditions as to where/when the origional set of data was collected, which includes air temperature, barometric pressure, etc., then you have a reasonable chance of adjusting the A/F ratio to a nominal value....or are you a proponent of stoichiometric combustion values as gospel? Again, a 1-2% excess air component is valuable to insure complete consumption of the fuel. However, because of the E-10 (or greater) component of the fuel (depending on brand/supplier) makes the A/F calculation a little more difficult to ddtermine. IMO...an A/F mmeter and the values derived is nice to know but should not be the only consideration used. I still maintain spark plug coloration provides the best overall average of the combustion efficiency, unless you want to install exhaust port temperature probes to insure even mixture distribution which would result in relatively even combustion OR perhaps a dyno run where all conditions can be observed and maximized and duplicated.
BOB RENTON

 

[Nate S]

Question: If you can insure the EXACT same conditions as to where/when the origional set of data was collected, which includes air temperature, barometric pressure, etc., then you have a reasonable chance of adjusting the A/F ratio to a nominal value....or are you a proponent of stoichiometric combustion values as gospel? Again, a 1-2% excess air component is valuable to insure complete consumption of the fuel. However, because of the E-10 (or greater) component of the fuel (depending on brand/supplier) makes the A/F calculation a little more difficult to ddtermine. IMO...an A/F mmeter and the values derived is nice to know but should not be the only consideration used. I still maintain spark plug coloration provides the best overall average of the combustion efficiency, unless you want to install exhaust port temperature probes to insure even mixture distribution which would result in relatively even combustion OR perhaps a dyno run where all conditions can be observed and maximized and duplicated.
BOB RENTON

First off, the sensors are really looking at CO and fudging the A/F. E10 may show as "14.0" when mixed properly at cruise even though it may be 13.5 in actual fact. Putting in actual straight gas would then make it go rich. Not available here anyway. As for the variables, these are variables if I don't look too. The carb today doesn't know all of these things exactly but still works. Just because this is a razor when I could use a butter knife doesn't make it a bad tool. I can quite easily fudge my jets for the average day (temp, humidity, altitude) I actually see and happily accept lean on cold days and rich on hot days etc. At least I'll know where I stand. Without looking, today I could be at 15.5 at cruise and 14 at WOT. Fairly simply I could get into the known acceptable ranges and be better off. It's a carburetor, I'll never be optimized for everything but I'd rather be optimized, or at least good for some condition of my own choosing.

 

[Kern Dog]

With my car, I've found that it makes more power when tuned to a number that traditionally should be considered too rich.
CA gas has what is listed as "Up to 10% Ethanol" yet tests of a couple of years ago have showed a 6% average.
I have a 440/493 with a Demon 850 VS, jetted at 83/92. I idle in gear around 13.5 to 14. Cruising at freeway speeds it is in the mid 13s. WOT drops down in the high 11s to mid 12s. When I tried to drop jet sizes, it slowed down. No smoke, no rich fuel smell. Plugs don't get sooty.

 

[beanhead]

The problem is the ethanol, yes, but also the other stuff in your available fuel. It's different everywhere...and I'm sure your aware of the seasonal blends. There is absolutely no substitute for proper plug reading. Newer more efficient engines aim for stoich, and that's fine, but when you get into bigger cubes, cams etc, the 'target' numbers go out the window.
My wideband says I'm pig rich at WOT. 10.9-11.2. My plugs say otherwise....

Sensor acting up? Possibly. Point is, if I started leaning based just on the gauge I could start hurting parts. I did experiment with leaning some, with a smaller pvcr and jets and it got weaker.
What the meters are great for, is keeping you informed of the mixtures once you know what the engine likes, as verified by plugs and..driving. It's recommended to use one that can display in Lambda, to rule out discrepancies between fuels.
And something that seems to not get mentioned enough is, a/f meters tell you zero about timing and heat range.

 

[Nate S]

While I have your attention, this is what a couple plugs show me. Depending on the way you look at them the story seems different. Note that this is only two plugs, white on one side, darker on the other. My sense is I’m 2-3 jet sizes lean.

 

[beanhead]

Ya know, I've had plugs do that too--color on one side, white on the other and I'm not sure what causes that. Burn pattern, strap shrouding, ignition, parted your hair on the left that day instead of the right..who knows. An easy check to ballpark the idle mix is to get it to a hot idle in gear and give the pump arm a quick gentle bump to squirt a little fuel in and see how the RPMs respond. If they momentarily increase, it's idling on the lean side. No change is in the happy place; a little slow-down and it's rich and didn't like the small shot of extra gas. At a glance I'd say those show a fat idle condition, jetting may be fine as evidenced by the color turn on the base ring but to really know the porcelain needs to be inspected down to the bottom, either by cutting the shell off or using one of those fancy lighted-magnifier doodads. If they're bone white down inside, then you're right on that it needs more jet and you can keep the WOT from getting crazy with the pvcr's.
I'm in the same boat as you; always looking for ways to get quicker feedback, no track close enough for meaningful WOT tests, and am always thinking "I bet it could be just a little better..."

 

[RJRENTON]

First off, the sensors are really looking at CO and fudging the A/F. E10 may show as "14.0" when mixed properly at cruise even though it may be 13.5 in actual fact. Putting in actual straight gas would then make it go rich. Not available here anyway. As for the variables, these are variables if I don't look too. The carb today doesn't know all of these things exactly but still works. Just because this is a razor when I could use a butter knife doesn't make it a bad tool. I can quite easily fudge my jets for the average day (temp, humidity, altitude) I actually see and happily accept lean on cold days and rich on hot days etc. At least I'll know where I stand. Without looking, today I could be at 15.5 at cruise and 14 at WOT. Fairly simply I could get into the known acceptable ranges and be better off. It's a carburetor, I'll never be optimized for everything but I'd rather be optimized, or at least good for some condition of my own choosing.

I guess it depends what type of sensor is providing the data and the methodology used to present the signal.
FYI....which you may recognise or not..... which type of sensor are you using to produce your data?
(From Google re oxygen sensors)....interesting information....
TYPES OF OXYGEN SENSORS
1. Zirconia sensor
The zirconium dioxide, or zirconia, lambda sensor is based on a solid-state electrochemical fuel cell called the Nernst cell. Its two electrodes provide an output voltage corresponding to the quantity of oxygen in the exhaust relative to that in the atmosphere.
An output voltage of 0.2 V (200 mV) DC represents a “lean mixture” of fuel and oxygen, where the amount of oxygen entering the cylinder is sufficient to fully oxidize the carbon monoxide (CO), produced in burning the air and fuel, into carbon dioxide (CO2). An output voltage of 0.8 V (800 mV) DC represents a “rich mixture”, which is high in unburned fuel and low in remaining oxygen. The ideal setpoint is approximately 0.45 V (450 mV) DC. This is where the quantities of air and fuel are in the optimal ratio, which is ~0.5% lean of the stoichiometric point, such that the exhaust output contains minimal carbon monoxide.
The voltage produced by the sensor is nonlinear with respect to oxygen concentration. The sensor is most sensitive near the stoichiometric point (where λ = 1) and less sensitive when either very lean or very rich.
The ECU is a control system that uses feedback from the sensor to adjust the fuel/air mixture. As in all control systems, the time constant of the sensor is important; the ability of the ECU to control the fuel–air ratio depends upon the response time of the sensor. Aging or fouled sensor tends to have a slower response time, which can degrade system performance. The shorter the time period, the higher the so-called “cross count” and the more responsive the system.
The sensor has a rugged stainless-steel construction internally and externally. Due to this the sensor has a high resistance to corrosion, allowing it to be used effectively in aggressive environments with high temperature/pressure.
The zirconia sensor is of the “narrow-band” type, referring to the narrow range of fuel/air ratios to which it responds.
2. Wideband zirconia sensor
A variation on the zirconia sensor, called the “wideband” sensor, was introduced by NTK in 1992 and has been widely used for car engine management systems in order to meet the ever-increasing demands for better fuel economy, lower emissions and better engine performance at the same time. It is based on a planar zirconia element, but also incorporates an electrochemical gas pump. An electronic circuit containing a feedback loop controls the gas-pump current to keep the output of the electrochemical cell constant so that the pump current directly indicates the oxygen content of the exhaust gas. This sensor eliminates the lean–rich cycling inherent in narrow-band sensors, allowing the control unit to adjust the fuel delivery and ignition timing of the engine much more rapidly. In the automotive industry, this sensor is also called a UEGO (universal exhaust-gas oxygen) sensor. UEGO sensors are also commonly used in aftermarket dyno tuning and high-performance driver air-fuel display equipment. The wideband zirconia sensor is used in stratified fuel injection systems and can now also be used in diesel engines to satisfy the upcoming EURO and ULEV emission limits.
Wideband sensors have three elements:
1. ion oxygen pump,
2. narrowband zirconia sensor,
3. heating element.
The wiring diagram for the wideband sensor typically has six wires:
1. resistive heating element,
2. resistive heating element,
3. sensor,
4. pump,
5. calibration resistor,
6. common.
3. Titania sensor
A less common type of narrow-band lambda sensor has a ceramic element made of Titania (titanium dioxide). This type does not generate its own voltage but changes its electrical resistance in response to the oxygen concentration. The resistance of the Titania is a function of the oxygen partial pressure and the temperature. Therefore, some sensors are used with a gas-temperature sensor to compensate for the resistance change due to temperature. The resistance value at any temperature is about 1/1000 the change in oxygen concentration. Luckily, at λ = 1, there is a large change of oxygen, so the resistance change is typically 1000 times between rich and lean, depending on the temperature.
As Titania is an N-type semiconductor with a structure TiO2−x, the x defects in the crystal lattice conduct the charge. So, for fuel-rich exhaust (lower oxygen concentration) the resistance is low, and for fuel-lean exhaust (higher oxygen concentration) the resistance is high. The control unit feeds the sensor with a small electric current and measures the resulting voltage drop across the sensor, which varies from nearly 0 volts to about 5 volts. Like the zirconia sensor, this type is nonlinear, such that it is sometimes simplistically described as a binary indicator, reading either “rich” or “lean”. Titania sensors are more expensive than zirconia sensors, but they also respond faster.

Anyway.....I'll continue to read my plugs to determine mixture ratios on the old GTX and for my 2020 Denali, I'll let the 4 O2 sensors and the engine management computer determine whats needed for the 6.2 liter 420 Hp engine to operate at peak efficiency and just enjoy the ride as we go down the road.
BOB RENTON

 

[Nate S]

I guess it depends what type of sensor is providing the data and the methodology used to present the signal.
FYI....which you may recognise or not..... which type of sensor are you using to produce your data?
(From Google re oxygen sensors)....interesting information....
TYPES OF OXYGEN SENSORS
1. Zirconia sensor
The zirconium dioxide, or zirconia, lambda sensor is based on a solid-state electrochemical fuel cell called the Nernst cell. Its two electrodes provide an output voltage corresponding to the quantity of oxygen in the exhaust relative to that in the atmosphere.
An output voltage of 0.2 V (200 mV) DC represents a “lean mixture” of fuel and oxygen, where the amount of oxygen entering the cylinder is sufficient to fully oxidize the carbon monoxide (CO), produced in burning the air and fuel, into carbon dioxide (CO2). An output voltage of 0.8 V (800 mV) DC represents a “rich mixture”, which is high in unburned fuel and low in remaining oxygen. The ideal setpoint is approximately 0.45 V (450 mV) DC. This is where the quantities of air and fuel are in the optimal ratio, which is ~0.5% lean of the stoichiometric point, such that the exhaust output contains minimal carbon monoxide.
The voltage produced by the sensor is nonlinear with respect to oxygen concentration. The sensor is most sensitive near the stoichiometric point (where λ = 1) and less sensitive when either very lean or very rich.
The ECU is a control system that uses feedback from the sensor to adjust the fuel/air mixture. As in all control systems, the time constant of the sensor is important; the ability of the ECU to control the fuel–air ratio depends upon the response time of the sensor. Aging or fouled sensor tends to have a slower response time, which can degrade system performance. The shorter the time period, the higher the so-called “cross count” and the more responsive the system.
The sensor has a rugged stainless-steel construction internally and externally. Due to this the sensor has a high resistance to corrosion, allowing it to be used effectively in aggressive environments with high temperature/pressure.
The zirconia sensor is of the “narrow-band” type, referring to the narrow range of fuel/air ratios to which it responds.
2. Wideband zirconia sensor
A variation on the zirconia sensor, called the “wideband” sensor, was introduced by NTK in 1992 and has been widely used for car engine management systems in order to meet the ever-increasing demands for better fuel economy, lower emissions and better engine performance at the same time. It is based on a planar zirconia element, but also incorporates an electrochemical gas pump. An electronic circuit containing a feedback loop controls the gas-pump current to keep the output of the electrochemical cell constant so that the pump current directly indicates the oxygen content of the exhaust gas. This sensor eliminates the lean–rich cycling inherent in narrow-band sensors, allowing the control unit to adjust the fuel delivery and ignition timing of the engine much more rapidly. In the automotive industry, this sensor is also called a UEGO (universal exhaust-gas oxygen) sensor. UEGO sensors are also commonly used in aftermarket dyno tuning and high-performance driver air-fuel display equipment. The wideband zirconia sensor is used in stratified fuel injection systems and can now also be used in diesel engines to satisfy the upcoming EURO and ULEV emission limits.
Wideband sensors have three elements:
1. ion oxygen pump,
2. narrowband zirconia sensor,
3. heating element.
The wiring diagram for the wideband sensor typically has six wires:
1. resistive heating element,
2. resistive heating element,
3. sensor,
4. pump,
5. calibration resistor,
6. common.
3. Titania sensor
A less common type of narrow-band lambda sensor has a ceramic element made of Titania (titanium dioxide). This type does not generate its own voltage but changes its electrical resistance in response to the oxygen concentration. The resistance of the Titania is a function of the oxygen partial pressure and the temperature. Therefore, some sensors are used with a gas-temperature sensor to compensate for the resistance change due to temperature. The resistance value at any temperature is about 1/1000 the change in oxygen concentration. Luckily, at λ = 1, there is a large change of oxygen, so the resistance change is typically 1000 times between rich and lean, depending on the temperature.
As Titania is an N-type semiconductor with a structure TiO2−x, the x defects in the crystal lattice conduct the charge. So, for fuel-rich exhaust (lower oxygen concentration) the resistance is low, and for fuel-lean exhaust (higher oxygen concentration) the resistance is high. The control unit feeds the sensor with a small electric current and measures the resulting voltage drop across the sensor, which varies from nearly 0 volts to about 5 volts. Like the zirconia sensor, this type is nonlinear, such that it is sometimes simplistically described as a binary indicator, reading either “rich” or “lean”. Titania sensors are more expensive than zirconia sensors, but they also respond faster.

Anyway.....I'll continue to read my plugs to determine mixture ratios on the old GTX and for my 2020 Denali, I'll let the 4 O2 sensors and the engine management computer determine whats needed for the 6.2 liter 420 Hp engine to operate at peak efficiency and just enjoy the ride as we go down the road.
BOB RENTON

Yeah, got it. I designed machinery for calibration and assembly of automotive sensors for Sensata Technologies for 11 years. I’m pretty familiar with the whole deal. At this point I’m not terribly concerned with burying myself in the base technology, I’ll look at the specs and pick what I need.

 

[coloradodave]

I just love the flashing lights on my AF gauge...

 

[RJRENTON]

I just love the flashing lights on my AF gauge...

And what do the flashing lights mean??? Count down to destruction or everything is normal or code for tonite's lottery number, or ???? "Inquiring minds want to know"..... just a thought.....
BOB RENTON

 

[coloradodave]

And what do the flashing lights mean??? Count down to destruction or everything is normal or code for tonite's lottery number, or ???? "Inquiring minds want to know"..... just a thought.....
BOB RENTON

With all the technical writing going on in this thread I thought I would go 180* the opposite way by stating that "tongue in cheek"... Guess I should have added an lol...

 

[Wietse]

I've been using the AEM wideband sensor for some time now, it is a nice add-on to see the A/F ratio and see what/were the mixture changes and what reading you get.
But do not try and chase the 14.7 ratio, at idle you will see it will run best with a richer mixture, mine does with 12.5 - 13.0 at idle.
If i try and bring it to 14 or so it will lean out to 16 - 17 when i throw it in gear (auto) and cause it to run like ****.
With sudden hard acceleration it dives down to 10 - 10.5, i've tried to play with jetting and i just cannot get rid of it and maintain a decent mixture under other circumstances.
If i go with smaller main jets it leans out to far and get hesitation.
While cruising i see 13.0 - 13.5, again, trying to lean this out with jetting causes problems.

Moral of the story is; Do not try to find the "perfect" mixture by going with the AFR reading, you can use it as a guide to see the changes you made by re-jetting and where the lean/rich moments occur during transition etc. but every engine will have a little different preference where it runs best.
If that means that under normal acceleration the AFR ditches to 10, does not stumble/hesitate/etc., so be it and you will have to kind of ignore the reading and go by how the car feels.

The 2 different colors observed on the plugs is caused by the fact that 1 side is exposed to the flame front and is kept clean.
The dark brown side faces the cylinder head and is not exposed to the flame as much.

 

[Nate S]

I've been using the AEM wideband sensor for some time now, it is a nice add-on to see the A/F ratio and see what/were the mixture changes and what reading you get.
But do not try and chase the 14.7 ratio, at idle you will see it will run best with a richer mixture, mine does with 12.5 - 13.0 at idle.
If i try and bring it to 14 or so it will lean out to 16 - 17 when i throw it in gear (auto) and cause it to run like ****.
With sudden hard acceleration it dives down to 10 - 10.5, i've tried to play with jetting and i just cannot get rid of it and maintain a decent mixture under other circumstances.
If i go with smaller main jets it leans out to far and get hesitation.
While cruising i see 13.0 - 13.5, again, trying to lean this out with jetting causes problems.

Moral of the story is; Do not try to find the "perfect" mixture by going with the AFR reading, you can use it as a guide to see the changes you made by re-jetting and where the lean/rich moments occur during transition etc. but every engine will have a little different preference where it runs best.
If that means that under normal acceleration the AFR ditches to 10, does not stumble/hesitate/etc., so be it and you will have to kind of ignore the reading and go by how the car feels.

The 2 different colors observed on the plugs is caused by the fact that 1 side is exposed to the flame front and is kept clean.
The dark brown side faces the cylinder head and is not exposed to the flame as much.

Super input! Thank you! What you’re saying about the ratio seems in sync with what others are saying too. A good thing to have in mind when I do this. The light/dark makes sense as well. Sounds like I should be reading the light side.