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Air Fuel Ratio


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#1 croc7

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Posted 12 July 2019 - 06:04 AM

I set my mixture to be about 14:1 at idle/cruise, 12-12.5:1 at fuel throttle. Thoughts?

#2 unburntfuelinthemorning

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Posted 12 July 2019 - 06:23 AM

Passion is the driver of potential.  You and I are pilgrims of the totality.



#3 danllew

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Posted 12 July 2019 - 08:48 AM

Sounds reasonable, this is a helpful article:

 

https://www.enginebu...rfuel-equation/

 

If you're measuring the AFR in the exhaust after its merged, then probably a bit safer to aim for the richer side.

The outer cylinders run leaner (function of the siamese ports) and if you;ve got a single lambda sensor you won't be able to pick that up.



#4 Moke Spider

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Posted 12 July 2019 - 09:28 AM

I'd say, on that limited info, it's a bit on the rich side but lean on idle.

 

Idle usually is a little rich for smoothness of idle, around the the 12.5 mark.

 

At what, I generally aim for 13:1 on a street car and for cruise, up around the 16.5 - 17.5:1.



#5 unburntfuelinthemorning

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Posted 12 July 2019 - 01:40 PM

Are you trying to achieve maximum power to the exclusion of all else, maximum fuel economy, maximum driveability, or a combination of all three?  What emissions standards are you required to adhere to?



#6 croc7

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Posted 13 July 2019 - 03:33 AM

Aiming for general good behavior in a mildly tuned 1360 with 10.5:1 compression, more performance rather than economy. No emission requirements here as the car is 25+ years old. Don’t want to burn a valve or on the other hand, wash down the cylinder walls.

#7 ACDodd

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Posted 13 July 2019 - 06:20 AM

Idle 13.5 to 13.8:1, cruise around 14:1, full power 12.5:1.

Ac

#8 unburntfuelinthemorning

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Posted 13 July 2019 - 06:24 AM

Aiming for general good behavior in a mildly tuned 1360 with 10.5:1 compression, more performance rather than economy. No emission requirements here as the car is 25+ years old. Don’t want to burn a valve or on the other hand, wash down the cylinder walls.

In that case I'd say 12.5-13:1 for full throttle to give maximum power, 15-16:1 is plenty weak enough for part throttle operation and adjust the idle mixture for the smoothest idle.



#9 croc7

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Posted 16 July 2019 - 06:50 AM

It’s kind of a juggling act between cruise, full throttle, needle selection, damper oil, spring, head, intake and exhaust, isn’t it? And for fun, let’s throw in crappy gas with ethanol.

#10 unburntfuelinthemorning

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Posted 16 July 2019 - 08:20 AM

Yes it is.  What percentage of ethanol do you have.  Mercifully ours is only up to 5% in our premium fuel at the moment but might increase to up to 10% in the years ahead.  Our higher octane super I don't think contains any ethanol but isn't as widely available.



#11 croc7

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Posted 17 July 2019 - 05:45 AM

15 %, although without is available, but only with 89 octane. Just completed a 3000 mile round trip to mini meet in Colorado (elev 8200’) and the car ran great with mixture adjustments along the way to compensate for altitude changes.

#12 unburntfuelinthemorning

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Posted 17 July 2019 - 07:19 AM

So you can run low octane fuel with no ethanol or higher octane fuel but with the problems ethanol brings such as lower energy density, storage, and corrosion problems.  That's a bit annoying.

 

Have you had it on a rolling road?






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