Air/Fuel Ratio Monitor • The Dodge Challenger Message Board

by **insuranceguy** » 30 Jun 2004 22:57

Installed an Edelbrock Air/fuel monitor, to help keep the carb fine-tuned. Found out that I was running way to rich. Then had to order the Carburetor Calibration Kit for the Thunder/AVS series, but the end result is a smoother running, little more efficient, and according to the seat of pants dyno, a lot more zip.

Highly recommend a fine tuned carb, it has been the single best gain I have found, other than throwing the 318 in the bushes... :roll:

Todd

by **papasan** » 01 Jul 2004 1:34

Will this work on a six pak? If yes, where can I get this?

by jr » 01 Jul 2004 7:23

papasan wrote:Will this work on a six pak? If yes, where can I get this?

It doesn't matter if you have sixpak or something else. You just install oxygen sensor to exhaust pipe right after headers/manifolds and wire display to cabin. Of course you'll only get readout from one pipe. I know that some people have installed two sensors and switch next to display so they can see numbers for both sides of engine.

by **dave-r** » 01 Jul 2004 7:31

I have written a lot on this board (and on its predecesor) in the past about the advantages of using one of these.

I recently replaced the edelbrock gauge on my car with a round Autometer gauge (keeping the original O2 sensor) as it matches the rest of my auxillary gauges.

I got both versions from Summit Racing.

Yes they work with any carb system. You have the same sensor on all your modern cars connected to the engine management system.
You just fit the sensor in the exhaust pipe.
Only works with unleaded petrol. No fancy fuels/aditives or alcohol if I remember right.

Use it to set your air/fuel mixture to around 13:1 under all conditions (read my threads on carb tuning) and your car will run as sweet as a nut.

by **dave-r** » 01 Jul 2004 13:29

This is the gauge I use. I worked out 13:1 is roughly in the middle of the rich scale (about 3 o'clock on this dial) but readings with these O2 sensors depends on how hot they get, the exact voltage they get, and how well they are earthed. You should always double check by looking at the plug colour.

This one has more LEDs than the Edelbrock unit (smaller steps between values) and matches my other gauges. You only get one led on at a time with this gauge so it seems to sweep around the outside edge of the dial. You do not get the exhaust sensor with this gauge. You do with the Edelbrock unit. But any O2 sensor will work.

by **insuranceguy** » 01 Jul 2004 16:31

Leaded fuels, or additive or alcohol will screw up the o2 sensor. I put mine in the head pipe, which is further away than recommended but seems to be dead on with external tester the shop has.

If your engine burns oil, you will get a false rich reading. I would recommend checking your plugs for fouling or ash if you get a funky reading.

It's a fun toy, though.... :lol:

by **dave-r** » 01 Jul 2004 18:08

A very usful tool more than a toy!

Glad you were able to reap the benifits Todd.

One problem with mine being in the lower dash.....

It is VERY hard to read when crossing the finish line at almost 120mph! :shock:

Somehow I always forget to look down at it. :roll:

by **insuranceguy** » 01 Jul 2004 20:55

Motley Crew had song, "10 seconds to love"... bet they were talking about racing a chally?

by **Christer** » 02 Jul 2004 7:53

$....

by **insuranceguy** » 02 Jul 2004 20:14

Poor attempt at humor. Trying to equate being to busy for 10 or 10 seconds to look at a gauge...

by **dave-r** » 03 Jul 2004 6:51

Don't give up your day job Todd.

by **bryan** » 03 Jul 2004 15:35

what does `stoich` mean?

by jr » 03 Jul 2004 16:31

bryan wrote:what does `stoich` mean?

Try http://www.sw-performance.com/Tech/1AirFuelII.html

Answer to your question (pasted from above page): 'The "perfect" ratio (not rich or lean) of air and fuel is called the Stoichiometric (STOICH) ratio.'

by **dave-r** » 03 Jul 2004 16:41

bryan wrote:what does `stoich` mean?

"Stoich" is short for stoichiometric.

A stoichiometric fuel ratio is one where that in theory you have the perfect amount of fuel to react with the amount of air you have so that they totally consume each other. In other worrds you are neither rich nor lean.
This ratio is 14.7 parts of air to one part fuel.

However in the real world combustion is never perfect. Therefore to get as much power out of the mixture as possible you are better off aiming for a mixture a bit richer of around 13:1 air/fuel.

Another thing. These sensors you put in the exhaust pipe are very good at measuring above (richer) and below (leaner) stoich. But at or around stoich they are very poor at measuring.

PLUS! The voltage the sensor puts out to light up the LEDs depends a great deal on the sensor temp.

Have a look at this graph. I have drawn a vertical line about where I wanted my mixture to try and see what sort of voltage I needed on the gauge. As you can see the voltage is less the hotter the sensor gets. So I aimed for a voltage of around 0.80 - 0.85 volts for a mixture in the 13.2 - 13.0 range.

by **dave-r** » 03 Jul 2004 16:45

On the AutoMeter gauge each LED lights up at a different voltage. In the rich scale the voltages range from 0.75 - 1.00 volt.

I aimed for 0.85 on my car which is at 3 o'clock on the dial. It just flickers the 0.80 LED as well. At idle it sometimes floats in the stoich area but that is fine.

My plug colour is very good so I am happy that I am in the right mixture area.

by **Christer** » 13 Feb 2005 18:28

Most of this article has already been covered I guess, but some additional information is never wrong!?

Oops, I almost forgot to tell that the article is fifteen years old, so it isn´t unlikely that some of it is out of date.

by **dave-r** » 13 Feb 2005 19:07

Shoot for 12.5:1-13:1 on your Mopar. This seems to give the most power.