12.7:1 A/F Ratio - Honda Motorcycles - FireBlades.org
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post #1 of 39 Old 06-12-2003, 7:33 AM Thread Starter
 
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Re: 12.7:1 A/F Ratio

Has anyone else other than KIDRR run into problems running the 12.7:1 A/F Ratio? *Just curious since i'm taking my bike to get it remapped next week using that ratio. I am going to take ratter's advice and run this ratio above 40%. I'll run it leaner below that (maybe at my current 13.2)



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post #2 of 39 Old 06-12-2003, 8:36 AM
 
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Re: 12.7:1 A/F Ratio

I ran mine at 12.5 to 12.8 and never had any problems anywhere throughout the range . . .
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post #3 of 39 Old 06-12-2003, 9:05 AM Thread Starter
 
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Re: 12.7:1 A/F Ratio

Abtech, did you use the 12.5 thru 12.8 all throughout (except for idle) or just after a certain throttle position (I.E - 30%, 40%, etc).
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post #4 of 39 Old 06-12-2003, 6:04 PM
 
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Re: 12.7:1 A/F Ratio

you have to remember that abtechs is a race bike, and normally fuel economy does not play a factor in setting a map in that sort of situation.

Do unto others, before some prick does it to you!

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post #5 of 39 Old 06-12-2003, 6:14 PM
 
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Re: 12.7:1 A/F Ratio

While my bike was never dyno'd itself...

THe map I ran was aiming for 12.6 or .7 EVERYWHERE except for idle. It ran perfect! Though refueling came with laughter from people I rode with. But a RC51 is bad about that anyway...
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post #6 of 39 Old 06-12-2003, 6:15 PM
 
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Re: 12.7:1 A/F Ratio

Quote:
scooper929 : Abtech, did you use the 12.5 thru 12.8 all throughout (except for idle) or just after a certain throttle position (I.E - 30%, 40%, etc).
Idle? we don't need no stinking idle . . .

I had the map set at this A/F ratio from idle to rev limiter.
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post #7 of 39 Old 06-12-2003, 6:23 PM
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Re: 12.7:1 A/F Ratio

Ok...I'll go ahead and ask...

I was under the impression that there was an ideal A/F ratio for gasoline engines (somewhere around 14.7:1) at which point the combustion was as efficient as possible (max power extracted).

Would someone explain to me why different engines would require a different A/F ratio, or where I'm going wrong? I'm fairly technical, so hit me with the good stuff.
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post #8 of 39 Old 06-12-2003, 6:27 PM
 
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Re: 12.7:1 A/F Ratio

Quote:
dB : Ok...I'll go ahead and ask...

I was under the impression that there was an ideal A/F ratio for gasoline engines (somewhere around 14.7:1) at which point the combustion was as efficient as possible (max power extracted).

Would someone explain to me why different engines would require a different A/F ratio, or where I'm going wrong? I'm fairly technical, so hit me with the good stuff. *
Ahhh...there's the kicker, most efficient does not mean most power in engine terms.

'Stoichiometric ratio' means you have equal parts of all of the chemicals needed to complete the reaction. Thus you have just enough fuel to combine with the air to burn.

It has nothing to do with making power!



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post #9 of 39 Old 06-12-2003, 6:31 PM
 
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Re: 12.7:1 A/F Ratio

ahhh, there's the word!

It's actually 13.7 to 1 (not 14.7) and a short walk through the pits at any NHRA National will have the folks on the floor if you mention it . . .
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post #10 of 39 Old 06-12-2003, 6:42 PM
 
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Re: 12.7:1 A/F Ratio

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abtech : It's actually 13.7 to 1 (not 14.7) and a short walk through the pits at any NHRA National will have the folks on the floor if you mention it . . .
If you don't fall over from breathing the unburned fuel dumping out of the exhaust pipes first.







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post #11 of 39 Old 06-12-2003, 6:46 PM
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Re: 12.7:1 A/F Ratio

Thanks guys, I'll do some more reading on the subject. I blame the EPA for my ignorance.
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post #12 of 39 Old 06-12-2003, 7:44 PM
 
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Re: 12.7:1 A/F Ratio

The optimum air/fuel ratio for a normal automobile is 14.7!

Not 13.7
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post #13 of 39 Old 06-16-2003, 8:33 AM
 
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Re: 12.7:1 A/F Ratio

NHRA ....AHHH thers nothing like the smell and sound of a 6000hp nitro burning engine!
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post #14 of 39 Old 06-16-2003, 11:46 AM
 
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Re: 12.7:1 A/F Ratio

My bad, although the following excerpt from an SAE white paper from the 1999 journals is usually the norm for engine tuning:

Air/Fuel Ratio *- The ratio of pounds of Air to pounds of Fuel needed for combustion in an engine. Air/Fuel ratio is based on pounds of AIR to pounds of FUEL but carbs are metered (jetted) by volume so changes in fuel can change A/F ratios. A/F Ratios range from about 2:1 for NitroMethane to about 16:1 for gasoline, with 14.7:1 considered the stoichiometric or chemically correct ratio under perfect conditions with normal (non-oxygenated) gasoline. *Gasoline A/F ratios for best power tend to be in the 13.25:1 - 13.75:1 range.

As you can see there seems to be a few variables in the above excerpt, which when combined with the various dissimilarities between automotive engines (relatively low compression ratios, relatively low RPM range, much smaller intake tract (throttle body volume vs displacement)) and contemporary sport bike engines, may account for the higher performance gained from lower ratios on the Blade . . .



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post #15 of 39 Old 06-16-2003, 12:27 PM
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Re: 12.7:1 A/F Ratio

I did a little reading in K. Cameron's 'Sportbike Performance Handbook' about the subject. He mentions the stoichiometric ratio of 14.7:1 but then goes on to say that optimum power will come in the 12-13.5:1 range. He goes through a bit of layman's chemistry but doesn't really explain why the richer mixture produces more power, except a quick blurb about the mixture having a larger volume. So presumably, there's not enough oxygen to burn all the hydrocarbons in a peak performing engine.
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