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What should the air/fuel ratio be at wide open throttle and idle?
 

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Wide open will make best power between 12.8 and 13.2 to 1 according to my Holley book. Don't know about idle but I would think about 15 or 16 to one. Bruce
 

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Right on with the WOT numbers

Idle shouldnt be all that much leaner, maybe up to 13.5-13.7. Problem is, if you lean the idle too much, the transition circuit will be too lean and it'll have a lean surge/buck at low rpm / light load

14.7 is the "theoretical" perfect air/fuel mixture for fuel to burn, however, not the most power and very dangerous for detonation in an non-computer controlled car

Shoot for mid 13's or lower numbers everywhere and you'll be good

<font size=-1>[ This Message was edited by: My427stang on 5/8/06 6:31pm ]</font>
 

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Ok Ross, and you other fella's... Wow do you come up with these #'s for AF ratios, and how can you tell what AF ratio your carb is putting out? I would LOVE to learn this tidbit of info, I can tune a carb by ear and feel and performance, but I cannot do it by the book and this bothers me to no end! Give me something to bite one please....

FE
 

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Only real way to check air/fuel ratio is with a wideband exhaust oxygen sensor... the next best being a narrow band, and the next best (crude, but better than nothig) is the spark plug read.

Oh and if you look around for some carburetor tuning literature, you'll find graphs of air/fuel vs. economy, air/fuel vs. power, etc... maximum economy is achieved at about 15:1 air/fuel, but max power is at about 13:1, and idle mixture has to be a little rich for reasons already stated, and simply because your engine doesn't atomize fuel or make very good cylinder pressure at idle.

_________________
'86 Bronco fullsize, 460, E4OD
'85 Ranger, 340hp 289, T5


<font size=-1>[ This Message was edited by: Motorhead on 5/9/06 12:16am ]</font>
 

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Motorhead hit it. Thats my reason to hit a dyno with the 489. Power numbers are nice, but the a/f mixture info is where its at.

Guys like Chilly and I think recently, Mike Burch, own relatively inexpensive wideband O2 dataloggers and they are slicker than even a dyno because you can record and log an entire session the way YOU drive

Thats my next toy. Besides that, no way to get the numbers from your car. (although I hear some guys take raw O2 sensor data and convert it using some sort of math, but for about 300 bones, the datalogger is pretty slick)
 

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Wideband's ROCK !!
 
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