Hi All,

Can the technically proficient people on the forum please explain air fuel ratio for me.

How to interpret it? What will be optimum? ...etc. Does not need to be 14R related. Please feel free to post up even if someone has already replied. All info welcome.

NB: this is not to start anything between tuners, just gathering pure information. There is a lot of us on here that ride our machines but do not know what a person must look for when buying after market goodies for the bike like exhausts and such... and how fitting certain products will affect reliability and performance. Sometimes things are bought totally unnecesary and sometimes necesary things are not considered.

Thanks in advance

Paul

Hey Paul, I hear ya man,

Air/Fuel Ratio:

This describes the ratio of mixture that is entering the combustion chamber via the fuel injection system. This 'ratio' determines not only how your bike will run, but also how it 'feels'.

Rich condition:A condition in which the mixture entering the combustion chamber has a GREATER amount of fuel to air.
ie: Anything showing as greater than 12.4:1 is a 'rich' ratio.

Lean condition:A condition in which the mixture entering the combustion chamber has a LESSER amount of fuel to air.
ie: Anything showing as lesser than 16.5:1 is a 'lean' ratio.

The first number: 13.1: 1 - is describing the volume of AIR
The second number: 13.1 : 1 - is describing the volume of FUEL

To clarify:

Any ratio showing a FIRST number that is LOWER than 12.4 is TOO RICH.
Any ratio showing a FIRST number that is GREATER than 16.5 is TOO LEAN.

Note: numbers used in example are examples.

* Last updated by: Cblast on 9/22/2013 @ 4:28 AM *

FUEL METERING

THE COMBUSTION PROCESS BURNS A MIXTURE OF AIR AND FUEL. THIS AIR AND FUEL MIXTURE IS REFERRED TO AS THE A/F RATIO. AS THE RELATIVE AMOUNT OF FUEL IN THE MIXTURE DECREASES ( A LEANER MIXTURE ) THE A/F RATIO VALUE BECOMES LARGER. AS THE PROPORTION OF FUEL BECOMES GREATER ( A RICHER MIXTURE ) THE A/F RATIO VALUE BECOMES SMALLER.

THE A/F RATIO OF AN ENGINE MAY BE MEASURED IN MANY WAYS, BUT THE MOST REPRESENTATIVE AND ACCURATE METHODS USE HIGHLY SPECIALIZED EXHAUST GAS ANALYZERS. THE A/F RATIO INFORMATION IS THE KEY TO ESTABLISHING AN APPROPRIATE FUEL METERING CALIBRATION FOR A GIVEN ENGINE COMBUSTION. ANYONE ATTEMPTING TO OPTIMIZE AN ENGINE A/F RATIO SHOULD PURCHASE AND UTILIZE AN A/F RATIO MIXTURE METER. WHETHER YOU ARE TUNING A CARBURETOR, FUEL INJECTION OR FORCED INDUCTION AND USING UNLEADED FUEL, THERE ARE MANY TO CHOOSE FROM, THE "WIDE BAND" VERSION IS THE PREFERRED VERSION. DO NOT DISCOUNT THE "NARROW BAND" VERSION, EITHER VERSION IS FAR MORE ACCURATE THAN "I THINK IT'S LEAN" OR "IT FEELS RICH", WITHOUT ACCURATE INFORMATION YOU ARE WASTING TIME, MONEY AND POSSIBLY THE ENGINE.

A FULLY WARMED UP ENGINE WITH AN A/F RATIO AS RICH AS 6.0-1 AND AS LEAN AS 22.0-1, THESE ARE THE GENERAL RICH AND LEAN COMBUSTION LIMITS, BUT DURING ACTUAL DRIVING SITUATIONS THE ACTUAL A/F RATIO NEEDED DURING VARIOUS OPERATING CONDITIONS WILL BE VERY CLOSE TO THE MID-POINT OF THESE EXTREMES.

A/F RATIO COMMENT

9.0:1 BLACK SMOKE (NO POWER)

11.5:1 RICH BEST TORQUE @ WOT

12.2:1 SAFE BEST POWER @ WOT

13.3:1 LEAN BEST TORQUE @ WOT

14.6:1 STOCHIMETRIC AFR ( CHEMICALLY CORRECT )

15.5:1 LEAN CRUISE

16.5:1 BEST FUEL ECONOMY (EXCEPT FOR HONDA MOTOR COMPANY)

18.0:1 CARBURETED LEAN LIMIT (EXCEPT FOR HONDA MOTOR COMPANY)

22.0:1 EFI LEAN LIMIT

GENERALLY ENGINES OF DIFFERENT BASIC DESIGNS HAVE THE SAME A/F RATIO REQUIREMENTS. THESE CALIBRATION NEEDS ARE TYPICALLY A FUNCTION OF OPERATION MODE, ENGINE TEMPERATURE, ENGINE SPEED, AND LOAD. GENERALLY A PRODUCTION BASED HIGH PERFORMANCE ENGINE WILL HAVE A/F RATIO VALUES IN A RANGE FROM 12.0:1 TO 16.0:1.

COLD ENGINE

THE COMBUSTION PROCESS REQUIRES VAPORIZED FUEL. MOST OF THE VAPORIZATION OCCURS AFTER THE AIR AND FUEL DROPLETS HAVE MOVED PAST THE INTAKE VALVE, BUT A LARGE PORTION MUST OCCUR BEFORE THE INTAKE VALVE OPEN. IN A COLD ENGINE THE AIR, FUEL AND ALL THE COMPONENTS CONTACTED BY THE FUEL ARE AT TEMPERATURES THAT DO NOT PROMOTE VAPORIZATION, SO ADDITIONAL FUEL MUST BE ADDED SO THAT THE PERCENTAGE THAT DOES VAPORIZE WILL SUPPORT COMBUSTION. THE AMOUNT OF THIS ADDITIONAL FUEL (COLD ENRICHMENT) DEPENDS ON THE TEMPERATURE. IF THE STARTING CLIMATE IS VERY COLD (-20F) THE A/F RATIO MAY NEED TO BE 4.0:1, AS THE ENGINE WARMS UP, THE A/F RATIO MUST BE LEANED TO NORMAL VALUES.

IDLE

THE A/F RATIO FOR A STABLE IDLE IS DETERMINED PRIMARILY BY THE CAMSHAFT PROFILE. A LONG DURATION CAMSHAFT WITH BIG VALVE OVERLAP CAUSES THE INLET CHARGE TO BECOME DILUTED BY EXHAUST GASES, THIS DILUTED CHARGE BURNS VERY SLOWLY AND MAY REQUIRE A LOT OF SPARK ADVANCE. ALSO THE COMBUSTION BECOMES ERRATIC, SO A RICH A/F RATIO IS REQUIRED TO REDUCE THE CYCLIC VARIATION (LOPING IDLE) WHEN TUNING. THE A/F RATIO MAY NEED TO BE 11.5:1 OR RICHER WITH A REALLY SERIOUS RACE CAMSHAFT PROFILE. WITH A SHORT DURATION CAMSHAFT PROFILE THE A/F RATIO DOES NOT NEED TO BE AS RICH FOR A STABLE IDLE AND MAY BE AS LEAN AS 14.7:1 WHERE EMISSIONS NEED TO BE A MINIMUM.

LOW SPEED AND LIGHT THROTTLE

THE CONDITIONS THAT AFFECT A/F RATIOS AT IDLE ALSO AFFECT THE FUEL CALIBRATIONS AT OFF-IDLE OPERATING CONDITIONS WHERE ENGINE RPM IS LOW AND THE LOAD IS LIGHT (LOW INLET DENSITY AND HIGH MANIFOLD VACUUM). AGAIN THE LONGER VALVE DURATION / OVERLAP, THE RICHER THE A/F RATIO WILL NEED TO BE FOR SURGE-FREE OPERATION. IN THE IMMEDIATE OFF-IDLE RANGE THE A/F RATIO MAY NEED TO BE AS RICH AS THE IDLE, SOMEWHERE AROUND 12.5:1 TO 13.0:1 IS COMMON, THEN GRADUALLY BECOMING LEANER WITH AN INCREASE IN SPEED OR LOAD. WITH A VERY MILD CAMSHAFT PROFILE, THE ENGINE MAY TOLERATE A/F RATIOS IN THE 14.0 TO 15.0:1 RANGE FOR THE SAME OPERATING CONDITIONS.

MINIMUM SPEEDS AND LOADS

AS ENGINE RPM INCREASES THE THROTTLE IS OPENED, THE EFFECT VALVE DURATION AND OVERLAP BEGIN TO DIMINISH. THERE IS LESS INLET CHARGE DILUTION, SO A LEANER A/F RATIO MAY BE USED WITHOUT ANY SURGES OR DRIVABILITY PROBLEMS. A/F RATIOS FROM 14.0 TO 15.5:1 ARE THE NORM. TYPICALLY THE BEST ECONOMY A/F RATIO IS FROM 15.5 TO 16.5 WITH A "STREETABLE" HIGH PERFORMANCE ENGINE COMBINATION, BUT WILL REQUIRE ADDITIONAL SPARK ADVANCE TO COMPENSATE FOR THE SLOW BURN RATES OF LEAN MIXTURES.

HEAVY LOAD AT PART THROTTLE

AS LOAD ON THE ENGINE INCREASES FROM ADDING MORE THROTTLE OPENING (HIGH INLET CHARGE DENSITY / LOW MANIFOLD VACUUM) THE A/F RATIO NEEDS TO BE ENRICHED TO PRODUCE MORE POWER AND REDUCE THE DRIVABILITY ISSUES BECAUSE OF LEAN A/F RATIOS AT HIGH LOADS. THE A/F RATIO SHOULD BE SOMEWHERE BETWEEN THE CRUISE AND WOT A/F RATIO VALUES, GENERALLY AROUND 14.5 TO 13.0:1 DEPENDING ON LOAD AND SPEED.

WIDE OPEN THROTTLE

ALL 4-CYLE GASOLINE ENGINES HAVE AROUND THE SAME A/F RATIO NEEDS AT WOT, WHERE THE GOAL IS TO PRODUCE THE MAXIMUM TORQUE / POWER FROM A GIVEN ENGINE COMBINATION. THE LEANEST A/F RATION THAT PRODUCES MAXIMUM TORQUE / POWER IS REFERRED TO AS "LEAN BEST TORQUE" WHICH IS USUALLY AROUND 13.3:1 A/F RATIO. THE RICHEST IS A A/F RATIO OF 11.5:1 "RICH BEST TORQUE". THE DIFFERENCE BETWEEN "LEAN BEST TORQUE" AND "RICH BEST TORQUE" CAN BE CLOSER AT HIGH ENGINE SPEEDS, SO THE BEST TARGET A/F RATIO FOR WOT USAGE IS BETWEEN 12.0 TO 12.5:1 A/F RATIO, THIS INSURES THE BEST PERFORMANCE AT WOT POWER UNDER ALL CIRCUMSTANCES.

SPARK ADVANCE REQUIREMENTS

THE CHARGE OF THE AIR / FUEL IS BURNED BY A FLAME-FRONT BEGINNING AT THE SPARK PLUG. THE FLAME STARTS A KERNEL WITH A RATHER SLOW RATE OF EXPANSION, BUT ONCE A SMALL PERCENTAGE OF THE CHARGE IS IGNITED, THE COMBUSTION PROCESS ACCELERATES AT A FASTER RATE. DUE TO THE VERY SLOW INITIAL REACTION RATES, IGNITION MUST OCCUR "BEFORE TOP DEAD CENTER" IF MAXIMUM EFFECT IS TO BE UTILIZED. THIS IS THE "ADVANCE" IN IGNITION AND IS MEASURED IN DEGREES OF CRANKSHAFT ROTATION. THE BEST ADVANCE USUALLY PRODUCES THE BEST TORQUE WHEN MAXIMUM CYLINDER PRESSURE IS ACHIEVED AT AROUND 15 DEGREES "AFTER TOP DEAD CENTER". DEPENDING ON DESIGN AND OPERATING CONDITIONS, THE SPARK ADVANCE CAN BE FROM LESS THAN 5 DEGREES UP TO MORE THAN 30 DEGREES FOR A HIGH PERFORMANCE / RACE ENGINE, AND 0 DEGREES UP TO MORE THAN 50 DEGREES FOR A STOCK PRODUCTION ENGINE WITH EMISSION COMPONENTS IN PLACE AND FUNCTIONAL.

THOSE OF US IN ENGINE DEVELOPMENT STRIVE TO CALIBRATE SPARK ADVANCE TO VALUES REFERRED TO AS " MINIMUM BEST TORQUE", THIS IS THE MINIMUM SPARK ADVANCE THAT WILL PRODUCE THE MAXIMUM TORQUE AT A GIVEN OPERATING CONDITION OF SPEED AND LOAD OF A GIVEN ENGINE COMBINATION. IN MOST CASES THE SPARK ADVANCE CURVE CAN BE ADVANCED SEVERAL ADDITIONAL DEGREES BEYOND "MINIMUM BEST TORQUE" BEFORE TORQUE BEGINS TO DROP OFF. IF "KNOCK" OCCURS BEFORE "MINIMUM BEST TORQUE" ADVANCE CAN BE DETERMINED. THE ADVANCE IS REFERRED TO AS "KNOCK" LIMITED. THE FUEL OCTANE, CAMSHAFT PROFILE AND OR THE ENGINE'S STATIC COMPRESSION RATIO WILL NEED TO BE ADDRESSED BEFORE MAXIMUM OUT-PUT CAN BE ACHIEVED.

THE VARIABLES THAT INFLUENCE THE SPARK ADVANCE REQUIREMENT INCLUDE THE BASE ENGINE DESIGN, THE SPECIFIC COMPONENTS OF THE PARTICULAR ENGINE ( CAMSHAFT, COMPRESSION, PISTON AND CYLINDER HEAD CONFIGURATION), THE INTENDED FUEL TO BE USED AND THE OPERATING CONDITIONS (RPM / LOAD / TEMPERATURES). THE SPARK ADVANCE GENERALLY INCREASES WITH ENGINE RPM UP TO A POINT WHERE IT WILL "PEAK" AND IN SOME CASES WILL DECREASE SLIGHTLY WITH FURTHER INCREASE OF RPM. ADVANCE REQUIREMENTS DECREASES WITH LOAD AND THE MINIMUM ADVANCE AT ANY GIVEN ENGINE SPEED IS AT WOT.

THE ADVANCE REQUIREMENTS OF AN ENGINE OF THE SAME DESIGN BUT DIFFERENT COMPONENTS ARE DICTATED MORE BY CAMSHAFT PROFILE, INCLUDING COMPRESSION. WITH A RADICAL CAMSHAFT PROFILE, THE WOT ADVANCE CURVE CAN BE VERY AGGRESSIVE AND REACH MAXIMUM ADVANCE AT A LOWER RPM BECAUSE OF THE POOR VOLUMETRIC EFFICIENCY AT LOW RPM, AND A VERY SLOW COMBUSTION RATE AND ITS HIGH RESISTANCE TO "KNOCK". PART THROTTLE ADVANCE ON ENGINES WITH LARGE CAMS CAN ALSO BE AGGRESSIVE BECAUSE OF THE REDUCED FLAME SPEED CAUSED FROM A SIGNIFICANT EXHAUST DILUTION OF THE INLET CHARGE FROM A CAMSHAFT WITH A LOT OF OVERLAP.

Thanks guys for taking the time to reply. Is appreciated.

No prob sir! I hope it helped, if not jut shoot me a line and I'll try to make it less gibberish.

Yeah...I was wondering about this as well...okay...I got it now...Thanks you all....very cool;)

C you lay it down for the novice. Well articulated. Romes lexiconal after reading C, I can follow yah, thank you!

Fuckin thank y'all for askin shit! :) I love trying to help about bikes. My wife is straight up sick of hearing about combustion and set-up etc.!!! Lol! She does call me Darth Torque though...

My wife is straight up sick of hearing about combustion and set-up etc.!!! Lol!

That's why we come here to continue rattling off what we want to say about fueling. Better warn the old lady, C, she can get snookered at the drive unless she knows hershit.

Lets look at a glass that is empty. Look at a glass that is filled to the top with water. Lets look at both glasses as a cylinder chamber. Lets look at the air as being thick as water, but you can't see that displacement.

Lettuce say it's there in liquid form, we drop the level from the top about a 1/8th inch. Lets say for argument sake, this is ideal 14.7 parts to one part of fuel. Lets say we now look at that liquid again, change it to air and when that ignites, there is part fuel, part air that adds up to a burned 14.7:1 AFRatio on the meter.

We are still in 'for argument'sake,' we fill that void again is the next cylinder charge. We are forever in this time delay----think. We sustain throttle, twist it to WOT, it took time to get there. We have thousands of revolutions happening, our WOT move is going to delay our cylinder being fed the next ratio [see posts above], but we are about to change ratios by that move.

Our delay time is less than a wink, meaning, a signal wave moves at light speed. So our coverter box [ECU] is going to take that wink to compute out the WOT which is no doubt fast in the computing. We add up the time delays [wrist-ECU-AFR], we need to look at our AFR meter as a 'delay' in time when we watch it in real time.

Getting back to those two filled glasses, we should notice something about them. When man designed these parts that evolved into fuel injection, there was this one formula they had to use, because they were stuck in this vacuum themselves living on dis earth.

So these laws also evolved and nature rules this particular one about this cylinder chamber. When man shoots for this number that gives this ideal chemical neutrality: it's not overrich, nor over lean. Man uses what I call, 'The Penultimate Number' that man is handcuffed to in FI [and everything else].

When the components breakdown, the ECU can still fill the fueling without those sensors. It calcs off the penultimate number it's handcuffed to. Lets get back to the 2 glasses. Glass air has pressure inside it say? It has 1 atmosphere. What is the pressure on top of the water in glass 2? The penultimate number sits on, sits inside both glasses for argue sake.

What does our cylinder chamber fill to when the valve closes without fuel in the chamber? You have to look at that glass as a cylinder chamber and know that is the penultimate number on the close: no fuel. How you displace that filled glass is when you can see it at the AFR = Your Ratio on either side of the penultimate... think.

WATT is 0 with key turned off, zero meaning 1 atmospheric pressure. The needle sits at 14.7 if it shows it sits on the 0.

WOT is 0 with Wide Open Throttle? 14.7 or 0. The needle swings to 0 @ WOT.

What is, 'For every action there is an opposite and equal penultimate.'

Cuts of the AFR and how I read it. I could be wrong, I'm still schooling myself.

13's ~ These were open throttle under heavy load. 13 and below were your power settings. No pig, stock pipes.

12's ~ Remember, lift is heavy vacuum too, so you can see the power banging 13, lift, delay, then you see the lift on vac hit in the 12.5 AFRange.

18's ~ This is a longer closed throttle. Little action so the AFRatio spikes a 'lets go back to idle, that throttle seems closed for too long, even though we have vacuum lift,' the logic assumes. So with TPS cranked off for that fraction, the AFR sees the ECU read that closed throttle number and there she sends that down to the [lean] 18's. Where you hear the fuel cuts off? No way. You'd air brake like a bandit. So the ECU sees how high that rpm is, how no action, meaning technically, the TPS is sending in one number. The closed number or a number with less fuel demand---time delay---oops! Back to WOT as if no time delay wattsoever we compute at light speeds.

15 AFR ~ Here is where I played with the air screws, ran them out some till I saw 15 AFR: at idle as I sunk them to that number. When you see key off, that saved the last sniff.

Just dam coooool Hubs!

Very nice Hub!

For every 0 upon WOT, there is an opposite and equal 14.7 swing is the answer of the penultimate number you are stuck with. See for yourself the very first basics of 760mmHg.

Even the ram effect zeros out to the 1ATMO, sans the low speed initial shock wave the sub might induce?

Harmonic frequencies/vibrations.

AFR ~ Open Loop:
The system runs simply in a linear fashion: like a rheostat light switch. Turn the throttle, you are @ 100 WATT when in WOT. Notice how there is no glitch or steady AFR reading. We have an open system that shows and stays at any linear position we want. We are tunable.

AFR ~ Closed Loop:
This system cuts off the linear at certain points. Closed loop sets a target and therefore closes down the open loop. It all has to do with start/idle/light loads. The euro 02 sensor replaces the atmospheric sensor that is under the seat of our bikes. Here are a few steps:

1. Cold start/Light load: Lets go back to an older part so you can see the evolution happen in the thought process. The first 02 concept was to wait for the sensor to heat up via the exhaust. Once heated it would recognize a wet and dry fuel signal. Call it a mini chemical reactor because that's watt it was made for: so electric signals can communicate.

a. Notice how the engine is still in open loop, the 02 has yet to build heat to make the chemical reaction begin. So @ cold start we are still in open loop till that old style 02 heats up.
b. Since there is going to be a rich mixture caused by the condensed, cold air, this will need more fuel to start and run. So as the engine warms, the signal begins. That was your single wire 02 technology back then. Now the 02 sensor is heated upon key on. A wire sends voltage to it's own heater inside the 02 body> It can begin to run leaner sooner as the air and water begin to warm up the engine.
c. When at cruising loads: you are not on the gas, nor off the gas. But what is happening in closed loop is if we were in open, we'd be running a more powerful 13 rich AFR. At that speed, the 02 is constantly spiking that throttle input, seeing you are off the gas and on the gas, so it targets a 14.7 ideal setting. As the 02 ticks off sniffing the difference between a rich and lean [analog open] move, into a [pinged closed] loop. This sniffing is termed the 'stoic,' or a number to represent the gas: via math. Air temp, water temp, this is going to set the fuel metering in a chemical way. That is part of the map plot and all those maps within maps. The 02 will just take those numbers and convert it to the chemical 14.7, i.e, The Penultimate.

2. Heavy load: Here is where the demand for fuel has to proportion out with the TPS and intake vacuum. 02 no longer is in closed loop. You are back to a sensor under heavy vacuum and that number intersects with the fuel delivery needed for that demand. Once the engine is back to low vac, cruise mode, the 02 kicks back in so you are back to best economy/best performance[to a point]/friendly emissions.

3. Learn process: The PCV with its 02, you are going to make a map, the V will learn to take those numbers, begin a learn process so those compute to a better/smoother/cleaner map. That's the theory. All my 02 doing is following open loop. It follows the OE map. It's just reading my throttle inputs. The only way to tell if the pcV's 02 cuts out is to see by WOT it does next? Since there is no vacuum to hook up to the V, my guess is the TPS calls the cutoff and the rpm answers that.

Too over the head or do you have the basics down? Because that is all she wrote.

Use is on your own, may the best map win.

* Last updated by: Hub on 9/23/2013 @ 10:50 PM *

See thats why I like Hub, he talks in a way I can understand.