Why AFR is important
AFR is responsible for generating an air fuel mixture that creates an efficient burn.
A rich AFR provides additional torque due to a faster flame front, cylinder cooling, can cause bogs/stumbling, and overall prevents a motor from burning up.
A lean AFR provides carbon cleaning (at cruising speeds), better fuel economy, raises cylinder temperatures, can cause a hanging idle, and increases knock sensitivity.
Note: AFR is not responsible for generating peak power to the extent to which timing is.
Okay now we understand the importance of picking the correct AFR.
What does a well made AFR table look like
A well made AFR table will command various AFRs throughout the RPM range. This should not be a constant value of 12.x across the board.
A richer AFR is desired at higher RPM to prevent knock and ensure the cylinders walls stay cool.
At idle we want a leaner AFR because there are less combustion events occurring.
In a cammed car you have an unstable idle due to low vacuum resulting in poor cylinder filling.
This means you will need to command a slightly richer AFR at to keep the engine running.
Now that we have an idea of how the AFR table should look, let's pick an AFR value.
Picking the actual AFR value
I've seen a 12.2-12.4 thrown around for 6.4 hemis.
I've seen 12.8 thrown around as an upper limit.
I've been told by hemi tuner (@mackBuilt on Instagram) that he shoots for low 11's (This seems insanely rich to me. Maybe this done to run some insane amount of timing?).
What I want to know is:
Q: How do we pick a target AFR in general?
It's great if someone comes in here and tells me that "Running an AFR of 12.2-12.4 is ideal for a 6.4L hemi."
What this doesn't tell me is how he or anyone else reached that conclusion. How do you find a baseline AFR for any engine? Start from stock and work from there?
I have also seen multiple people claim "See what the car responds best to."
What data are we logging here? Butt dyno? 0-60 E.T? I'm looking for a scientific approach here.
Q: What is an acceptable range of AFR values? 0.5? 1.0?
Going from 13.0-12.0 seems like a large swing.
Going from 12.4-12.2 seems like a small swing.
Maybe I am over emphasizing the importance of AFR in this context, however I believe only experienced tuners can answer these questions.
Also, here is a link to the xml spreadsheet that can help you calculate your current and desired AFR.
This has been supplied by 06300CSRT8
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Originally Posted by LilSick
