Ideal Air/Fuel Ratio?

[Lucky34]

I searched a bit looking for what the best A/F ratio was, and found that 13.1 was about the magic number (I assume for a busa). Would it make a difference on a 1000?

For a 2006 GSX-R1000,
What A/F ratio should I be at and when? Example, should I have 13.1 at the start of the RPM range and then around 12.0 near the end (to compensate for RAM air)? Or try and hold a steady A/F ratio throughout the whole rpm range?

 

[Robot]

Wow, what a great question! As a Cessna pilot and Aviation enthusiest, I would question what "ideal" means. Perhaps ideal horsepower?

In a normally asperated aircraft, leaner mix will get you more miles per gallon but also run hotter. Normally fuel cost is included in the hourly rental cost of an aircraft, so the pilot is not motivated to save money by running lean.

Typically a Cessna pilot would monitor exhaust gas temperature, lean the mixture to max exhaust temp, then enrich to 100 degrees fahrenheit off/below peak temp. How this temp equates to optimal HP, not sure. Thats about the extent of my air/fuel mix knowledge.

I bet you get all sorts of good info on this question

 

[bigoltool]

Somebody smarter than me will chime in here any second but heres my take. True Stoichiometric combustion ( if I remeber correctly) would be something around 14.7:1 (pretty lean) but from what I read the fuel injection systems around today simply cannot hold that number steady throughout the rev range so most tuners aim for around 13 or 13.5:1 as a bit of a safety measure. The problem is that there are so many variables involved (Intake Air temperature, atmospheric pressure, fuel pressure, fuel injector flow rates etc. etc. ) is almost an impossibility to nail it down. So almost all maps are slightly compromised in one area or another. I am sure some day Wide band O2 sensors and super sophisticated fuel metering systems will exist for us mortals that could allow you to get a little closer to the mark.

Wikipedia link.

 

[Lucky34]

I dont have permission to edit my post, so here's the new questions:


What is the best (most hp) A/F ratio for a K6 1000 (stock)?
What is the best (safest for the engine) A/F ratio for a K6 1000 (stock)?

Does spraying nitrous change those "best" A/F ratios or is the goal of a "good tune" is to have the A/F ratio the same when on and off the nitrous?


And finally, does any of this change between the GSX-R1000 and the Hayabusa? Or can we look at this as a combustion engine. Period. I believe that stoichimetrically the ideal Air/Fuel ratio for a gasoline and oxygen combustion is 14.5 or 14.7, but we try running low 13's and 12's to be safer? More fuel is better than more air, right? More air = lean = engine blows?

 

[99'busa]

 my 2 cents has already happened but i await more info

my further 2 cents i cant confirm right now so i will

for the time being

 

[proud dad]

I dont have permission to edit my post, so here's the new questions:


What is the best (most hp) A/F ratio for a K6 1000 (stock)?
What is the best (safest for the engine) A/F ratio for a K6 1000 (stock)?

Does spraying nitrous change those "best" A/F ratios or is the goal of a "good tune" is to have the A/F ratio the same when on and off the nitrous?


And finally, does any of this change between the GSX-R1000 and the Hayabusa? Or can we look at this as a combustion engine. Period. I believe that stoichimetrically the ideal Air/Fuel ratio for a gasoline and oxygen combustion is 14.5 or 14.7, but we try running low 13's and 12's to be safer? More fuel is better than more air, right? More air = lean = engine blows?

14.7 is the average A/F on a cruise not WOT a big differance.12.8 - 13.1 is the target A/F you want AT WOT.And to run Nos it has to be way richer[don't know how much].
I've seen a LS2 GTO maintain a 14.7 average on a cruise but go to 10.8 WOT[stock tune,straight flow mufflers,before tune]

14.7 does not mean 14.7 all the time,that won't work.That's gas engines in general.

 

[Lucky34]

Very true... I got a dyno run of the stock bike, with a slip-on, no PC or tune or anything... and it showed at first the AFR dipped to like 13.5, then up to about 15 and slowly down to 14.0 by the end... So I definitely think I'm running rich.
I'm going to try to make it so I hit 13.1 at the beginning, and then down to around 12 at the end (but since the dyno can't really duplicate the ram air, even though in the dyno it gets richer near the end, in the real world there will be more air coming in, so it'll balance out).
Also, for when spraying nitrous, I found somewhere that it should be between 11.5-12.0 AFR.

This is pretty cool that I started researching nitrous... I would have never started thinking about this Air/Fuel ratio stuff... which is really the most important thing on the motorcycle...

 

[Johnnycheese]

you set to at what the motor wants not to some number

 

[Spudley]

and the "CHEESE" has spoken !!!! My sentiment exactly......

 

[Lucky34]

I think I've got an idea of around where it should be... now only dyno + tune can tell me what the engine likes most

 

[SANDFLEA85]

I have a 2 1/16 digital a/f ratio gauge if anyone is iterested (can be mounted on a tiger raceing gauge plate attached to tripple tree top clamp),still in box.I decided not to punch a hole in my brand new Brocks pipes...$80tyd....chrome bezel/blackface.red readout!! pics upon request.

 

[GPW]

I have a  2 1/16 digital a/f ratio gauge if anyone is iterested (can be mounted on a tiger raceing gauge plate attached to tripple tree top clamp),still in box.I decided not to punch a hole in my brand new Brocks pipes...$80tyd....chrome bezel/blackface.red readout!! pics upon request.

Just the gauge or the 02 sensor as well......

 

[runeight]

I have a  2 1/16 digital a/f ratio gauge if anyone is iterested (can be mounted on a tiger raceing gauge plate attached to tripple tree top clamp),still in box.I decided not to punch a hole in my brand new Brocks pipes...$80tyd....chrome bezel/blackface.red readout!! pics upon request.

I'll get behind greg on this one please.

r8

 

[Commuta_Busa]

The task of finding the ideal ratio is difficult because of the sensitivity of gasoline in combustion. The spread between the a/f ratio producing lean best torque (LBT) and rich best torque (RBT)is the range of ratios over which the engine produces best torque. This is componded if the engine requires extra fuel for combustion cooling and/or knock control. The WOT ratio range between RBT and LBT is typically 11.5-13.3. The spread narrows at high rpms as highest possible flame speed becomes increasingly critical to achieving complete combustion in the reduced amount of time.

Power and flame speed vary greatly with the a/f ratio. Peak power with gasoline occurs just rich of rich best torque (RBT) just above 11:1. The cooling heat of vaporization of such rich mixturesalong with the high flame speed help fight detonation.

At high loading and WOT richer mixtures give better power by making sure all air molecules in the combustion chamber have fuel present to burn. Since the best torque mixture spread narrows at hgher engine speeds a good goal is 12.0-12.5, richer if fuel is being used for combustion cooling. Mixtures of 13.0-13.5 A/F typicaly give better driveability depending on loading and speed.

Gasoline does not burn as a single homogenous molecule that burns with oxygen in a precisely predicatble manor. Given unlimited time for combustion and perfectly mixed batch of fuel/air it takes 14.68parts of air to 1 part gasoline in a reaction that produces 100% efficiency. 14.7:1 A/F is the chemically correct ratio or stoich. In a high speed engine there is limited time for combustion. The air and fuel are not perectly mixed. Some gasoline molecules will not be burned and some air will not find any fuel to burn. Best power always occurs when there is at least a small fuel surplus above stoich becasue air is the scarce commodity. The best power strategy is to make sure there is enough fuel available so that virtually all of the air that enters the engine will be able to burn fuel.

Engines make the most power when you lean them out. Working carfuly for every HP will sometimes run higher than 13.1:1 a/f but these mixtures are more dangerous. This kind of tunning makes an engine more sensitive to cariations in altitude and relative himidity. These engines produce higher cylinder pressures. The higher stress on mechanical parts results in more thermal loadingto the cooling system which can increase the tendency for detonation. Peak torque makes the most cylinder pressure and requires slightly richer mixtures than peak power. To optimize tunning it's always good to start at a known over-rich setting and then leaning the mixture until torque falls off slightly and then moving in the rich directino until you ahieve peak torque.

Alot of factors take part in determining the ideal ratio. Volumetric efficiency, spark timming, fuel pulse width, cams, etc. Also remember that it's still a compromise unless you can calibrate air/fuel/spark for each individual cylinder.

 

[Tybalt71]

great info