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AFR tuning


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#1 ucw458

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Posted 21 May 2019 - 08:58 PM

I always thought the best power was when your AFR is right on the edge of detonation.  Turns out that's not really true.  Acording to the dyno results in this video richening the mixture for a better safety margin doesn't come with a big power loss penalty.  These tuners are using lambda measurements so you'll have to convert the numbers.


http://www.youtube.c...Lrn-2jyw&t=248s
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#2 scott87star

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Posted 22 May 2019 - 09:02 AM

I think you mean best power when timing was on the edge of detonation, which isn't correct either but timing is far more correlated with detonation than air fuel ratio.  To wring the most out of a motor you tune AFR first with a conservative timing table because engines run pretty well with a wider range of AFR, then go back and work on optimum timing for power.
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#3 Woody

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Posted 23 May 2019 - 07:00 PM

scott is correct. AFR has been proven to not make more or less power. Running richer helps to keep the car cooler which helps stop detonation, and leaning out detonates. But it's really the timing which gives you more power. But only to an extent. Being right on the edge of detonation isn't always what you are chasing.

Usually you want to adjust the timing to ignite so that you get most of your power on the downward stroke. It's when it ignites and it's still on an upwards stroke that you get knock. Too soon knocks, too late lacks power. It's a balance to move the needle as much as you can before power results start slipping back. But on turbo applications you will usually hit knocking point before reaching the point where your power starts going backwards.

Tuning the AFR is mainly for fuel economy. Having it as lean as possible is to save fuel. Not give you more power :)
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#4 Turbo Cary

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Posted 24 May 2019 - 08:03 AM

Another thing to consider with AFR tuning is emissions if you live in a state that requires testing. Running rich increases hydrocarbons while running lean will increase your NOx readings. It basically requires a balance. When you're leaner the cylinder temps are higher which produces more NOx thus the reason cars had EGR valves. Cars no longer use EGR valves for the most part due to variable valve timing.

#5 Technology

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Posted 30 May 2019 - 09:17 PM

Extra fuel is also used to reduce heat sometimes. My tune would go rich if the temp got above a certain number, something like 200 or 210 degrees I think.
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