A/F Ratio - Kawasaki ZX-10R.net
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post #1 of 5 Old 01-09-2005, 10:12 PM Thread Starter
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A/F Ratio

I was a bit confused last week when discussing A/F ratios and what nubers were lean and what was rich. I can't ever stand not knowing so I did some research. I figure if I was confused, someone else may be also. Below is from an article on Dragbike.com about a digital A/F meter mounted on a nitrous Busa. I think it gives a decent explanation.

>>>>>>>>>>>>>>>>from article<<<<<<<<<<<<

...what is this A/F ratio gauge Iím talking about? The A/F gauge measures the ratio of air to fuel that is being burned in your combustion chamber, or even simpler put, how lean or rich you are. For you more technical folks, the air-fuel ratio is the weight ratio of air to fuel (gasoline) drawn into the cylinder during engine intake stroke. If you are putting too much fuel into your motor, you are in a rich situation, too little fuel and your running lean. Too little and you burn stuff up, too much and you donít have the power you want, it smokes, it gurgles, and a host of other things that happen when youíre too rich. The optimum ratio of Air to Fuel is about 13.5 pounds of air to 1 pound fuel. At this point, we have stoiciometry or the point at which the most complete combustion takes place.
AF = (mass of Air) / (mass of Fuel)

Below is a chart in which the Air/Fuel ratio gauge measures your exhaust gases and itís corresponding voltage signal. Notice that at 14.5:1 the chart shows youíre A/F Switch shutting off your Nitrous when it becomes too lean. I will explain the switch in just a moment.

Full Throttle


Dangerously lean 14.6:1
Very lean 14.5:1
Max power (Lean) normally aspirated 14.2:1
Max power normally aspirated 13.5:1
Max power (Rich) (NOS, Blower, Turbo) 13.2:1
Very rich 12.5:1

Last edited by miykl; 01-10-2005 at 09:34 AM.
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post #2 of 5 Old 01-09-2005, 10:47 PM
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Good post.... now go get ya shit right and and put the spankin on that R1!!
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post #3 of 5 Old 01-09-2005, 10:52 PM Thread Starter
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The graph didn't paste over correctly, but I think the numbers tell the story. As for getting my shit right, I dropped the bike off at Mike Cats Saturday on my way out of town to have the map done. A/F of 13.0/1 being targeted as suggest from the tuning link guide Mike has. I pick it up tomorrow evening.
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post #4 of 5 Old 01-10-2005, 06:48 AM
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either you have some unusually fast bikes in your area or...

Over here in S. FL I race GSXR's, R1's,RR's, 954's, everything

The only way I lose is when I get the front too high and come off the gas.

I would say I win 90% of the races I get into.

I ride with about 10 guys on 1000's and am certified as the fastest bike in the group.

With all the shit you are doing to your bike you HAVE To have a faster bike than me (Unless removing your butterflies hurt your bike)

I am very curious to ride with you in May.

The last night I rode my bike was the day I changed my gearing (that night I was thinking that the bike was geared too low as the front seemed to hate the ground)

Luclky I'll get some more seat time before the Gap and will change my gearing if it is not setup correctly.

I have no idea what my ratio is. My guys tuned my bike old school.

Loaded a recommended map, went leaner and leaner untill power was lost, then slightly richer.

Not much science there.

ya ya ya...
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post #5 of 5 Old 01-10-2005, 09:13 AM
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Good write up, not always the case with different fuels, each fuel has it's own stoich ratio. 93 unleaded is not the same stoich as 108 fuel. 14.7, 13.7, is not actually the voltage of the sensor. It is converted in a calibration table. Sensor voltage is between 2 and 3.5 volts, on a ntk sensor and ntk controller 14.7 is 3 volts. not all controllers have a linear table either. The bosch sensor is pretty linear on the cal curve but the ntk sensor is not, it is a parabolic curve. Anyway, 14.5 is lean but dangerous is really not until about 15 or more. There is compression with these motors but there is not much bore size. Totally agree with about 13.5.

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