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Old 01-10-2010, 02:20 PM   #1 (permalink)
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Ideal AFR

What is the ideal AFR we should be seeing on a NA car? What should they be like under Vtec and under normal driving conditions? What are the danger zones in being rich and lean? I would greatly appreciate it for anyone who can answer.

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Old 01-10-2010, 03:00 PM   #2 (permalink)
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I'm no pro, but I've done enough street tuning and research to provide you with a solid, safe answer--

The ideal ratio of air to fuel is 14.7 parts air to 1 part fuel, or 14.7:1, referred to as stoichiometric combustion (or just "stoich.") When balancing between efficiency and safety, this is best, and you should aim for it at both idle and cruising RPM (or as close as possible.)

Under heavy load and/or VTEC, everything under your engine bay becomes hotter, and will continue to rise in temperature depending on how prolonged the load is (track racing, etc.) Due to the high-revving nature of Honda engines, they are typically tuned to run rich in VTEC, since the extra fuel acts as a coolant in the combustion chamber. You want to aim for 12.x:1 in VTEC at full throttle (closed loop.) This is too rich for ordinary load conditions, though.

Running lean is GENERALLY more risky than running rich. Anything above 14.7:1 could be considered lean, and above 15.0:1 is pushing it, whereas running 14.0:1 (for example,) while rich, is not something to be terribly concerned about.


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Old 01-11-2010, 05:01 PM   #3 (permalink)
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Quote:
Originally Posted by enojy View Post
I'm no pro, but I've done enough street tuning and research to provide you with a solid, safe answer--

The ideal ratio of air to fuel is 14.7 parts air to 1 part fuel, or 14.7:1, referred to as stoichiometric combustion (or just "stoich.") When balancing between efficiency and safety, this is best, and you should aim for it at both idle and cruising RPM (or as close as possible.)

Under heavy load and/or VTEC, everything under your engine bay becomes hotter, and will continue to rise in temperature depending on how prolonged the load is (track racing, etc.) Due to the high-revving nature of Honda engines, they are typically tuned to run rich in VTEC, since the extra fuel acts as a coolant in the combustion chamber. You want to aim for 12.x:1 in VTEC at full throttle (open loop.) This is too rich for ordinary load conditions, though.

Running lean is GENERALLY more risky than running rich. Anything above 14.7:1 could be considered lean, and above 15.0:1 is pushing it, whereas running 14.0:1 (for example,) while rich, is not something to be terribly concerned about.
OP...

14.7 for normal driving

12.9 for Wide Open Throttle/Open Loop up to about 7500 rpms
12.6 for Wide Open Throttle/Open Loop from 7500 & up
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Last edited by Dan0974; 01-11-2010 at 05:03 PM.
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Old 01-11-2010, 06:19 PM   #4 (permalink)
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Quote:
Originally Posted by Dan0974 View Post
OP...

14.7 for normal driving

12.9 for Wide Open Throttle/Open Loop up to about 7500 rpms
12.6 for Wide Open Throttle/Open Loop from 7500 & up
Thanks for info. I assume this is for tuned cars, do you know what honda set it to on a stock car?
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Old 01-11-2010, 06:21 PM   #5 (permalink)
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Quote:
Originally Posted by Dan0974 View Post
OP...

14.7 for normal driving

12.9 for Wide Open Throttle/Open Loop up to about 7500 rpms
12.6 for Wide Open Throttle/Open Loop from 7500 & up
Lol, I'm running a good bit leaner than that at WOT. 12.9 is what I would shoot for on my turbo car.
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Old 01-11-2010, 06:27 PM   #6 (permalink)
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i'd stick to stoich for part throttle. for an all motor car at full throttle i play it safe and aim for 12.8. with forced induction cars i aim for 11.8. this is on pump gas. things change when using other fuels such as e85.

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Lol, I'm running a good bit leaner than that at WOT. 12.9 is what I would shoot for on my turbo car.
that's way too lean for my liking.
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Old 01-11-2010, 11:52 PM   #7 (permalink)
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I've been at 13.2 wot till 8500 with no issues for months now.
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Old 01-12-2010, 01:19 AM   #8 (permalink)
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I've been at 13.2 wot till 8500 with no issues for months now.
For at least 5 yrs here. Four in my K20Z1 and one in my K20Z3
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