Wideband AFR gauge installed

[JimNiki]

Guys, I've just installed a wideband Air Fuel Ratio gauge.

It's on my 351 with auto and 750 vac sec Holley.

It smells a little rich, was just hoping the gauge could shed some light.

I'm interested in values at warm idle, slow acceleration, wot?

Any thoughts?

cheers and thanks again...

 

[sicndhed]

I’ll share some general comments I’ve come up with after using an Innovate wide band as a tuning aid for about ten years. IMO AF readings are a great way to get in the ballpark when tuning a vehicle but I no longer get too fixated on what the gauge says. The best WOT is not any particular AF reading, it’s whatever number allows the vehicle to accelerate the best. On a carbureted car you will probably be surprised when you see how much your idle mixture screw setting impact your steady state cruise ratios. The lesson there is since you spend a lot more time cruising than idling, getting cruise optimized is more important than having the leanest idle. In many situations added fuel is a band aid but it’s a band aid that can work as long as you’re not add enough fuel to load up the spark plugs or wash cylinder walls. For a while I struggled with theoretical targets while not having good tip in characteristics. Adding a little fuel past the number that chemistry says is right fixed the issue. Enough fooling around with air bleeds and idle restrictors probably would have allowed a leaner cruise but I find tuning to usually fall into the 90-10 rule. 90% of the results come from the first 10% of the effort. If I had only one vehicle I’d probably make a career out of optimizing its carb but I need to move on to other projects at some point. Tuning a big cam in a car with overdrive almost always has me spending the majority of my time working on high gear low RPM light to moderate acceleration.

Two important things to remember are: proper ignition advance is often the cure for low rpm issues and in a typical AF gauge installation you are looking at the average of four cylinders. If two cylinders are running rich and two are running lean on the bank with the sensor, the gauge will tell you that everything is “perfect” even though none of the cylinders are optimized.

 

[TommyK]

This graph illustrates typical values for a fuel curve on a carbureted engine. As sicndhed notes, stoich (14.7:1) is irrelevant when tuning a carb. Rich and lean can only be described in the context of what the engine needs at any given point of throttle opening and load to run correctly.

When tuning use the wideband to quantify and compare relative changes. Don't get hung up on a number. The goal is not to hit a number, it is to tune the carb to provide smooth operation at all throttle openings while achieving the best power and economy. How the car drives and how the plugs look are ultimately most important.

 

[mustang7173]

All,

I had a friend mention this device and started to look up the information on this device. My question is , if you are running dual exhaust with cross over, where do you mount the sensor?

mustang7173

 

[TommyK]

All,

I had a friend mention this device and started to look up the information on this device. My question is , if you are running dual exhaust with cross over, where do you mount the sensor?

mustang7173

Either side upstream of the crossover, as close to the header collector as possible. Theoretically you should pick the side which has the leanest running cylinder based on plug reading.

I put mine on the side that had the easiest access.

 

[MeZapU]

I've done a substantial amount of tuning using widebands on my cars. Two main things to note is:

I had significant issues correlating plug color to the AFR because the Autolite spark plugs of today are not the same as the ones of just a decade ago. The "made in USA" logo was quietly removed and the good old copper core Autolite plugs are now made abroad. I would be reading lean on the wideband but the plugs would be indicating rich. I was chasing my tail because of the incorrect ignition properties of the Autolites. I cracked one during tuning and I substituted the whole set with a used set of NGK's I had lying around. After that I was floored with the results. No more misfires and the plug color correlated with the AFR readings. I chased that rabbit for about a year.

AFR for todays E10 fuels is 14.1:1 and not the typically stated 14.7:1 of a 100% dino fuel. After this discovery I shifted all my target AFR's to the left approximately .6 of a number I was pleased with the results on how the engine responded. EFI cars compensate for this automatically. With a carburetor this difference must be accounted for via tuning.