Air/ Fuel Ratio

[Lazzman]

Of the guys who have had their sohc Explorers Dyno tested Aldive, Spindle etc... What was your A/F ratio reading through the rpm range?

What should the ideal ratio be?

Thanks

 

[BrooklynBay]

14.7-1 is the ideal fuel-air ratio. This is called stoichiometry. They sell gauges for this that you could add.

 

[Lazzman]

Thanks Brooklyn.

I always thought mine was to low, the readings I got all three times while on different Dyno's, two Dynojet Research models and a Mustang AWD model all recorded my a/f at 12.5:1 seemed to rich for me on a very slightly modified engine.

According to the charts at my min a/f ratio of 12.3-1 I made 15% less horsepower and torque then I did when the max a/f was recorded at 12.6-1, I think my numbers would go up considerably if I could get it to the 14.7-1 that is optimum.

 

[aldive]

My best power was at 13.4.

Here is a sample of the AF plot. Notice how flat it is across the range.

 

[spindlecone]

12.7, with my mods and tune worked for me

 

[aldive]

Further my best mileage tune was at 13.2.

 

[aldive]

I think my numbers would go up considerably if I could get it to the 14.7-1 that is optimum.

No

 

[Turdle]

At a 14.7:1 ratio it will SCREAM







for a second or two.

 

[aldive]

At a 14.7:1 ratio it will SCREAM







for a second or two.

If that long.

 

[aldive]

14.7-1 is the ideal fuel-air ratio. This is called stoichiometry. They sell gauges for this that you could add.

A theoretical number; not real world. Way too lean.

 

[Lazzman]

Surprising that only 2/10th of a point increase could yield 15% more power. I also believe that around 13.5 would be optimal for the intake, exhaust, chip deal.

My chart was like Al's straight and even though the line was 12:1 rather than 13:1.

I am sure I have a vacum leak somewhere that is screwing up the calibrated a/f ratio. My suspiction leads me to the upper and lower intake O ring gaskets.

 

[aldive]

I also believe that around 13.5 would be optimal for the intake, exhaust, chip deal.

Based on what? No way of knowing with running on the dyno with good AF instrumentation.

I am sure I have a vacum leak somewhere that is screwing up the calibrated a/f ratio. My suspiction leads me to the upper and lower intake O ring gaskets.

Pull the intake an fix it then.

 

[spindlecone]

The best A/F ratio is where you make the most H.P and TQ. without detonation.

 

[gijoecam]

Indeed, 14:1 at WOT near redline is WAAAY too lean. A lean-burn runs WAY hot, and exhaust gas temps can melt manifolds among other things. Running it a bit rich (in the 12-12 range) is normal and yes, while it doesn't make as much power, the extra fuel helps cool the combustion chamber significantly. Running 14:1 will cook the internals in no-time. I;ve seen it burn holes in the tops of pistons.

-Joe

 

[wpurple]

I run between 14 and 15 normal driving, WOT or under boost I drop to 11.5 to 12.3

I am using a AEM wideband gauge. The factory o2 sensors are narrow band, such that the engine management is just going between add fuel/don't add fuel trying to achieve about 14.7.

 

[TheJMan]

Wouldn't the amount of ethanol that is added to our fuel also lower the stoichiometric ratio? According to my calculations, if 100% gasoline has a 14.7:1 ratio, and ethanol has a 9:1 ratio, this would result in a mixture (given that there is 10% ethanol) with a stoichiometic ratio of 14.1:1.

So in this case 14.7:1 is too lean.