Lean Idle

General engine tech -- Drag Racing to Circle Track

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1972ho
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Lean Idle

Post by 1972ho » Sat May 12, 2018 9:55 am

Are there any problems with a drag race only engine having the idle O2 at a air fuel 18 plus.It also could be the O2 sensor being to close to the exit of the merge collector the exhaust also has some reversion because when I place my hand near the outlet it wants to suck my hand into the collector.

rp930
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Re: Lean Idle

Post by rp930 » Sat May 12, 2018 10:26 am

Open exhaust will surely affect the O2 reading at idle and possibly elsewhere.

77cruiser
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Re: Lean Idle

Post by 77cruiser » Sat May 12, 2018 11:12 am

Set it for best idle & ignore the reading at idle.
Jim

jeff swisher
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Re: Lean Idle

Post by jeff swisher » Sat May 12, 2018 11:35 am

No issues I ran as much as 20.5 at idle and this was with full exhaust.
I ran as lean as 18.5 with a Q jet at part throttle cruise and that is the point it began surging from being too lean.

Lots of advance and iron intake.
This was checked on a wheel dyno with the sniffer in the tail pipe.

You are not under load so being lean at idle hurts nothing in my book.. unless it is surging and bucking.
But I have not seen that happen at idle.
Not yet anyway.

peejay
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Re: Lean Idle

Post by peejay » Sat May 12, 2018 11:38 am

If the idle isn't dead smooth, ignore the O2.

O2s read oxygen in the exhaust, not "fuel mixure". Any misfires will make it read lean. Also any exhaust leaks will make it read lean.

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