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Discussion Starter · #1 ·
I am trying to optimize my 750 MightyDemon annular on my 468, 9.5, 248/238 big block. I have an Edelbrock air/fuel gauge which shows if it's lean or not. I am always in the 13 ratio, when I know that 14.7 is optimal. The car runs great anywhere from 68 to 66 jets main, 74 to 71 secondary. I say "great", how do you tune when you get fully into the mains and you're going 60+ mph a few seconds later? It's pretty frantic.

Anyway, changing the main jets hasn't changed the reading of my AF meter. Yes, it is reading something, it actually reads one LED leaner at idle, and the reading changes if you rev the motor.

So, for you guys blessed with dynomometer resources, have you notice any repeatable correlation between a jet size and a ratio change? Like jump one size and change .4:1 or anything like that?
 

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Discussion Starter · #3 ·
I don't know the diff between wide and narrow, it's 3 wire sensor though. doesn't that mean it's heated, that's gotta be better so maybe it's wide? The range is 11:1 to 15:1 with 7 leds indicating the reading. Way rich is 2 yellows, "OK" 13:1 to 14.7:1 are green, meltdown lean beyond that is red. I am always in the yellows, below 13:1, even with those rediculously small #66 jets. (I am at 4300' elevation)
 

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Your gauge is narrow band by your description.

I doubt the LED lights will give you enough information to tell the difference between or 1 jet size change, much less 2.

The general concensus is 12.8 to 13.2 is the A/F number for max power/ET. The engine definately won't make power at 14.7 to 1 and I'd bet you'll burn it up running that lean. I won't run mine any leaner than 13.5 at WOT on the high gear pull. I try to stay around 13.0 or so and watch the mph on the time slip.
 

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why do you care about stoich? My car cruises the freeway just fine at 16.5:1 A/F ratio. Stoich is just an ideal setup for catalytic converters. Your car have a cat on it?

for power you need 12.5 - 13.2, richer is better if there's doubt.

the narrow band O2 won't tell you anything much, just which side of 14.7 you're on. The Innovate WBO2 is cheaper than carb..... with the price of gas it might pay for itself.
 

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Discussion Starter · #7 ·
I care about stoic because... I dunno.... just because it's there. I cared before with the auto trans because it would bog when I would punch it, and I couldn't ever get it right. But now when I punch it with the 5speed, the wheels just spin :yes: That should be good enough, huh? It just bugs me that changing 2 jet sizes doesn't show up on my meter at cruise speed and rpm.

Also, since I have to pass emissions testing, I would like an accurate one to help me with the pre-test tuning.

So what does wide band mean compared to narrow band? I see the Innovates on eBay for $300 for the sensor and gauge.
 

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Wanted to add a little or discuss a little more on stoichiometric.

Since stoichiometric is 14.7 this means that a gas motor has it highest combustion efficiency with this ratio. The maximum energy from the air and fuel mixture is being obtained with this ratio. After the chemical process of combustion has occured, the maximum energy has been obtained from both the air and the fuel. Stoichiometric is different depending on fuel. Stoichiometric for a diesel is around 22:1. Something people rarely talk about is a/f ratio with diesels. Modern diesels idle at something like 60:1 or more, I know it sounds lean. If you had a/f ratio on the x axis of a graph and cyl temps on the y axis, you would see a bell curve and the max cyl temp would be at 14.7 for a gas engine. Cyl temps go up as you approach 14.7 and go down descending from 14.7. A engine with 12:1 mixture would not produce as much combustion energy as the same engine with 14.7:1. Because of compression, volumetric efficiency, cam timing, etc. a high performance motor needs a richer mixture, to prevent detonation and high cylinder temps, by using the fuel to cool. I think we use the term leaning out loosely. We know we need a richer mixture for a high performance, but when guys say they are leaning out, I think they are referring to approaching 14.7, and not meaning exceeding 14.7. The nitrous guys and boost guys need more fuel because of increased oxygen and air density, as well as to cool.

I have always wondered about this and did a little research. If there is anybody out there that knows the theory and relationship between cyl temps and a/f completely I would be all ears.....always have wondered.

As far as wideband and narrow band, I not sure the exact difference. I think automotive uses a narrow band which is just the 02 sensor, which creates a voltage that ECU reads. .45V equals stoichiometric ratio and as voltage changes, the ECU changes fuel delivery by pulse width and duty cycle of injectors. I think wideband uses a lambda probe which is a lot more accurate. Here again not sure...just chiming in.

THANKS
ANDY
 

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a wide band will read afr's over a much bigger range on the order of 9 to 17 to one where as the one you have is really only accurate around around 14.7 it will show that its leaner or richer than that but its not accurate. they were made to keep closed loop fuel mixtures at light cruise at 14.7 in fuel injected and feed back carb cars
 

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I care about stoic because... I dunno.... just because it's there. I cared before with the auto trans because it would bog when I would punch it, and I couldn't ever get it right. But now when I punch it with the 5speed, the wheels just spin :yes: That should be good enough, huh? It just bugs me that changing 2 jet sizes doesn't show up on my meter at cruise speed and rpm.

Also, since I have to pass emissions testing, I would like an accurate one to help me with the pre-test tuning.

So what does wide band mean compared to narrow band? I see the Innovates on eBay for $300 for the sensor and gauge.
you can buy the lc-1 for $199 and use your current gauge with the lc-1s analog outputs.
 

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a wide band will read afr's over a much bigger range on the order of 9 to 17 to one where as the one you have is really only accurate around around 14.7 it will show that its leaner or richer than that but its not accurate. they were made to keep closed loop fuel mixtures at light cruise at 14.7 in fuel injected and feed back carb cars
Exactly, a narrowband was only designed to tell a vehicles pcm which side of 14.7:1 it is at.....above or below, it does not actually measure AFR......The three wire ones are heated which just allows them to operate sooner.
 

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Discussion Starter · #12 ·
Exactly, a narrowband was only designed to tell a vehicles pcm which side of 14.7:1 it is at.....above or below, it does not actually measure AFR......
But again, the Edelbrock gauge has 7 LEDs, 2 yellow "way rich", 4 green "OK", and 1 red "uh-oh". It idles with the 2 yellow off, and the richest of the greens flickering, and the rest of the LEDs on. If I rev it, they will instantly all light indicating that the accelerator pump addes some extra. Then on the rev decel, they will all turn off as very little fuel is going in. I think. Anyway, it's not just one for rich, one for OK, and one for lean.

I still need a different sensor system?

I don't know why I get so caught up in this stuff. It runs fine, has more power than I ever get a chance to use with my type usage. It's neck snapping crisp, doesn't smoke black on acceleration, doesn't smoke back at idle. I ought to just forget about it. The only thing bugging me about the car is deceleration surging (throttle closed). But that may be the car bucking back and forth on the system backlash....
 

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does the sensor jump around or is it steady?
 

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Discussion Starter · #14 ·
It's steady for a steady state running condition. Change the RPM, and it will change. It indicates that it idles leaner than it cruises (no yellow rich leds at idle, one at cruise).
 
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