Honda Motorcycles - FireBlades.org banner

12.7:1 A/F Ratio

4K views 38 replies 17 participants last post by  deez 
#1 ·
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)
 
#5 ·
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...
 
#7 ·
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.
 
#8 ·
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!
 
#10 ·
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.
 
#14 ·
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 . . .
 
#15 ·
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.
 
#18 ·
Hmm...I've been thinking about this and have a couple of thoughts as to what MAY be happening.

The first is the cooling effect of the increased fuel. More fuel in the mixture will cool the ports and cylinder head as it flows in.

The second is the effect of the extra fuel on scavenging. There are situations where I could envision an extra bit of fuel in the headers will change the backpressure on the engine.

I have no idea if these effects are real and could help. Just brainstorming...

Trying to return from deep left field now.
 
#20 ·
Just had my 929 Remapped again. I gained 2HP from going from the 13.2:1 A/F ratio to 12.7:1. I did not use 12.7 all throughout. I used 12.7 for 40% and more trhrottle and over 6K RPMs. Since my 929 is not a race bike, I wanted some fuel economy for cruising. Anyway, thought i'd let everybody know. 12.7:1 is definately good.
 
#21 ·
scooper929 : Just had my 929 Remapped again.  I gained 2HP from going from the 13.2:1 A/F ratio to 12.7:1.  I did not use 12.7 all throughout.  I used 12.7 for 40% and more trhrottle and over 6K RPMs.  Since my 929 is not a race bike, I wanted some fuel economy for cruising.  Anyway, thought i'd let everybody know.  12.7:1 is definately good.
Lady made a mistake telling me the numbers on the phone. It actually lost 2 HP, not gained. Not sure if the technician adjusted properly. I was told if I was going from 13.2 to 12.7 to simply subtract 5 from whatever was in the cells that I wanted to adjust (in my case 40% and greater for throttle and > 6K rpms). It seems like the technician added 5 to these cells. Was I given correct info. Is adding 5 correct or should he have subtracted 5. I.E 40% @ 7000 rpm said -5 in my 13.2:1 map. In my 12.7:1 map, the same cell said 0. I was expecting it to have -10. What do you guys think??
 
#22 ·
The tech did it right if he added 5.  Adding positive integers to the amount on the chart richens the mixture, which is what you are doing when going from 13.2 to 12.7.  I'm still fuzzy about what actually happened.  Did the change increase the HP or decrease it?

It also sounds like you may have the pair system still engaged, please tell me you don't, as you cannot accurately (or even remotely for that matter) measure A/F ratio with the pair system active (it injects air into the exhaust system for pollution control).
 
#25 ·
scooper929 : The change actually did decrease the HP by 2.  As far as the Pair valve goes, it's still intact.  I never did do the pair mod?  I was under the impression that doesn't really make a difference.  Should I do it?
It should have been blocked or disconnected to get accurate a/f ratio readings. With it connected ,although the sensor may read 12.7:1, it may have actually been a lot richer than that ie it may have been 11.5:1, would would explain the loss of power (too much fuel = loss of power, too little fuel = loss of power)
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top