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by FordMuscle Staff

If you're running a carbureted Ford and you haven't seriously considered
any of the Air Fuel measuring devices found in the www.fordmuscle.com tech department archive, we know why. Air Fuel meters appear too complicated, require too much software, provide too much information, and cost too much money. Unfortunately, these barriers prevent many traditional Ford enthusiasts from using this tool to confirm they're running the right jets, power valve, and have their idle mixture screws out the optimum number of turns.

Air Fuel meters have long been a device used by tuners who are mostly
younger and more "techy" than old school Ford hobbyists like most of us. Since a great portion of the tuner crowd rarely gets beyond cold air intakes, performance chips, and exhaust systems, "data logging and laptopping" with robust Air Fuel meters and bundled software offers them a way to personalize their motors much the way we do with camshaft selection. While we are not here to say which group produces more legitimate hot rodders, we are here to say that if you are not using the basic functionality of an Air Fuel meter to tune your carburetor then you're probably pissing in the wind everytime you pick up that long skinny flathead screwdriver.

Innovate Motorsports DB Gauge
This compact Wide Band Air Fuel gauge kit from Innovate Motorsports includes the basics for capturing Air Fuel data. The controller is built right into the cable. While the kit includes data logging software in addition to the 02 sensor and gauge, the cost and simple install make it perfect for simple "live" data tuning. Retails for $289.00.

Air Fuel Meters Dumbed Down
The key to eliminating your hesitation about purchasing, installing, and using an Air Fuel meter on your carbureted Ford starts with looking past manufacturer emphasis on data logging and all the boring software screen shots found
in their marketing materials. Many of the most powerful Air Fuel meters on the market use handheld or nontraditional displays since a tuner's tuning decisions are expected to be made from LOGGED data via a laptop computer. As the Air Fuel Meter market evolves, a few manufacturer's have recognized that not all enthusiasts are terribly concerned about or have the time to study logged Air Fuel data. This is especially true for carbureted street machines who's owners just want to be sure their naturally aspirated motor isn't running too lean or too rich without going to the dyno. In reality, all a traditional street enthusiast needs from their Air Fuel meter is the ability to:

Accurately measure Air Fuel Ratio
Display the "real-time" Air Fuel Ratio
Easily mount the Air Fuel Ratio gauge

The Innovate Motorsports dB Gauge pictured above right is a nice compact unit that fits these basic requirements at a reasonable price. Take note that there is no control box since the brain is built right into the cable.

Live Data Tuning with the ACCEL DFI
The ACCEL DFI Wide Band 02 Kit is a perfect example of a data logging device who's manufacturer understands the need for a mountable gauge even with their most capable Air Fuel meter. While this unit offers more configurable features than most carbed enthusiasts will ever need, the digital gauge does allow you to start tuning immediately from live data (via gauge feedback). For most, this may be the only way they ever use an Air Fuel meter. However, the benefit of a high-end unit like this one is that once you get comfortable live tuning, you then have the option of analyzing 15 channels of logged data with the included DataMap software and ACCEL's Gen 7 logging feature. Another unique feature of the ACCEL DFI Wide Band 02 Kit is its ability to trigger external devices based on RPM, vehicle speed, and Air Fuel Ratio. For now however, let us show you how we got the 650cfm Holley atop our Torino's 351C dialed in with just live data from the ACCEL DFI Wide Band 02 kit.

ACCEL DFI Wide Band O2 Kit Single Channel With Gauge
PN 77062S

After installing the ACCEL unit on the Torino, the first step was to determine target baseline Air Fuel Ratios for idle, cruise, and wide open throttle. The following table was pulled from the ACCEL DFI instruction booklet. The table is by no means an absolute reference for the perfect Air Fuel Ratio for all applications. However, the information provided serves as a great baseline for experimenting to see how idle mixture, primary jet, power valve, and secondary jet adjustments impact power, economy, and drivability. The row highlighted in tan best represented our 351 Cleveland's profile and most street performance Ford V8's. With the chart as a guideline we focused on the first and easiest carb adjustment. What else but idle mixture?

Recommended Baseline Air Fuel Ratio Chart
Engine Type
Stock - little or no modification to engine, 87 octane gasoline
Street/Strip engine - naturally aspirated, performance camshaft and exhaust, 10.0 - 11.0 compression, premium pump gasoline
Race Engine - naturally aspirated, high lift/duration cam, 12:1 or higher compression, high flow heads and exhaust, high octane race fuel


In This Article...
Don't let laptops, software, data logging, and information overload prevent you from purchasing an Air Fuel meter to tune your Holley carburetor. FordMuscle breaks down even the most stubborn "old school" Ford man by using only "real-time" (no data logging) air fuel feedback to dial in a Holley.

Wide Open Throttle
Kevin Mikelonis offered his 1972 Torino as a test vehicle to use a simplistic "real-time" Air Fuel tuning approach.

After installing ACCEL's Single Channel Wide Band O2 Kit with gauge, we took the Torino on some backroads for both cruising and wide open throttle runs. Turn up your speakers and listen to the "bird disrupter" as we read our Air Fuel ratios. See Video

Taking real-time note of the Air Fuel Ratio at idle, cruise, and wide open throttle, we virtually had all the information we needed to dial in the 650cfm Holley atop the Torino's 351C. While this particular ACCEL Wide Band 02 meter is capable of much more, we didn't need a computer to make key Air Fuel observations via the digital gauge.

This video shows real-time Air Fuel data prior to any carb adjustments. From the video you'll see the carb was running proportionally rich but was leaning out during transition from cruise to wide-open throttle. See Video










Idle Mixture Tuning
One of the "thrills" of installing an Air Fuel meter on your carbureted Ford for the first time is seeing how far off your idle mixture screws have been all these years. Since time began you may have been going through the same routine of backing off your idle mixture screws as if you really knew what you were doing. Or, maybe you're car has been running just fine with the factory idle mixture preset. Whatever the case, the chances are once you get a good Air Fuel reading then you'll see that your carb can use at least some minor idle mixture adjustment.

Another interesting part of getting quantitative feedback from and Air Fuel meter is finally being able to equate what a quarter turn, half turn, or full turn of a Holley idle mixture screw actually does to Air Fuel ratio. Like the chart on the previous page, the graphic below is not a hard and fast rule but just what we experienced with this combination. Somewhat interesting was that our test vehicle's rich idle condition was cured with just a quarter turn of lean adjustment (clockwise).

The ACCEL DFI Wide Band controller is durable enough to be mounted in the motor compartment. We tied back the serial cable since we were just going off real-time gauge feedback.
As noted in the illustration above, once the entire unit was installed, the gauge indicated a rich idle condition with an Air Fuel ratio of 12.6:1. This photo was taken with the Torino in park idle.

Here we are searching for the correct lean adjustment to bring the idle Air Fuel ratio close to 14.2:1.
One quarter clockwise turn of each primary idle mixture screw brought us from 12.6:1 all the way to the recommended baseline of 14.2:1

There it is, we just set the idle mixture confidently and without the use of a laptop or data logging software.

Tuning for Cruise (power valve and primary jet adjustments)
With the easy idle adjustment out of the way, we looked to the primary metering circuit to dial in Air Fuel ratio at part throttle or cruise. Since we were originally running rich during all three driving conditions, we took on the power valve before making jet changes in order to confirm that the power valve was not coming on too early. If you have the incorrect power valve for your motor's vacuum and load behavior, then chasing a target Air Fuel ratio with jet changes is a fruitless venture.

A power valve is designed to supply additional fuel (as much as 10 jet sizes) during low vacuum and high load conditions, like transitioning from cruise to wide-open throttle. However, as indicated by the in-car video on the previous page, we suspected our power valve was coming on too late (low rated power valve) causing a lean condition during the transition from cruise to wide-open throttle. Take note of the slight hesitation and the short rise of Air Fuel ratio to 15.6:1 when the accelerator is fully depressed during the video.

For a street performance V8, a power valve that opens 2 inches (Hg) below the lowest steady cruise vacuum reading is most appropriate. A number 6.5, 7.5, or 8.5 power valve often works well on stock or slightly modified engines like our Torino's Cleveland. The lowest vacuum level we observed at cruise was between 8 and 9 inches (Hg). We cracked the primary bowl to see what we had, expecting to find a power valve rated below 6.0 inches (Hg). Here's what we found.

Sure enough, a 4.5 power valve was the culprit causing our lean-out from cruise to wide-open-throttle.
Based on the real-time feedback we received from our Air Fuel gauge and the vacuum reading observed during cruise conditions, we installed a 6.5 power valve.

Now that we were confident with our power valve selection, we moved to the primary jets to correct the rich condition we had during cruise conditions. Remember, even though we were leaning out when transitioning from cruise to wide-open throttle, our Air Fuel gauge indicated a rich 13.6:1 ratio DURING cruising.

This 650cfm Holley came equipped with number 68 jets in the primary.
Since we were running a tad rich during cruise (13.6:1), we replaced the number 68 jets with number 66 jets.

With a more appropriate power valve and smaller primary jets installed, it was time to road test for Air Fuel ratio during steady cruise and during transition from cruise to wide-open throttle.

With a 6 inch (Hg) power valve rather than a 4.5 inch (Hg) our Air Fuel ratio did not rise above 12.7:1 when mashing the gas during cruise. Note that vacuum is at or near zero during this condition.
With the "lean" jet change we never dropped below 14.0:1 while cruising.

Tuning for Wide-Open-Throttle (secondary jet adjustments)
In our particular situation, the wide-open-throttle Air Fuel ratio was near optimum before any carb adjustments were made. Bouncing between 12.6:1 and 13.0:1 to start, the primary jet adjustment we made to lean our cruising Air Fuel ratio affected wide-open-throttle just enough to put us in a range between 12.8:1 and 13.2:1. If we found our Air Fuel ratio to be off by a full point or more during wide-open-throttle, the process of making secondary jet adjustments, up or down two at a time, would have been done.

Here's a shot a wide-open-throttle. The primary jet adjustment we made previously was enough to increase our average Air Fuel ratio at wide-open throttle to 13:0.1. No secondary jet adjustments were required, this time.

Ready to get yourself an Air Fuel meter now? We hope so. The intent of this article was to show that logical adjustments can be made to your Holley carburetor without trial and error tuning or worse, the fear of learning a new software program in order to sift through logged data. And don't worry, an Air Fuel gauge mounted in your carbureted Ford doesn't make you a tuner! Tell us what you think in the comments box below.

Posted by myfast5oh, 07/13/07 09:47pm:
Excellent ! no more guessing...
Posted by sobill, 07/14/07 07:08am:
Well done and well explained.
Posted by Juan, 07/16/07 07:51pm:
Nice article. I contacted ACCEL and they never heard of the unit.
Posted by Mikelonis, 07/17/07 10:13am:
Juan, The part number and the link are in the article. Did you try those? Jon
Posted by Juan, 07/17/07 06:26pm:
Jon. No, I did'nt try the link. Will do so this evening. Thank you. Juan.
Posted by Gearhead99, 07/22/07 02:26pm:
Great article. Have to get one of those.
Posted by hellfirejim, 07/22/07 02:36pm:
I thought it was an excellent article. Brings up the question: why doesn't somebody make the wideband setup without the data logging part. You bypassed it and it would lower the price? I don't need the data loging but want to set up my carb. Thanks jim
Posted by markafss, 07/23/07 05:25pm:
I am assuming the same general technique can be used with a Edelbrock carb also? It would be just knowing which screws and valves to tweek?
Posted by Mikelonis, 07/24/07 01:51pm:
markafss, Yes, the same technique would be used. See this article for how idle mixture, primary metering, cruise-to-WOT, and secondary metering are controlled on the edelbrock carb. http://www.fordmuscle.com/archives/2005/08/EdelbrockCarburetor/
Posted by 91tbird, 06/26/09 10:56am:
so many question have been answered for me since i have been looking into purchaseing comp cams fast tuneing meter thankyou guys so much
Posted by geronimo, 04/28/11 07:32am:
Yesterday I installed an AEM A/F ration meter in my 65 Mustang. This unit costs $200 from Summit Racing and does not have the data logging part (although you can data log with it if you have a laptop computer. I'm printing this article and going out to the car and start making adjustments. Thanks for the article.
Posted by e-tek, 03/06/12 08:04pm:
5 year old article and A/F gauges are now getting poular. I just bought the Innovate uit for $245 CDN and will install it this week.

Before You Start!
Be sure you are working with a clean air filter before you take initial Air Fuel readings. A clogged air filter can cause a rich condition even when mixture settings are ideal.

In our case, we ran the reusable 14"x5" filter on the Torino through K&N's recommended cleaning procedure.



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