What is the ideal air fuel ratios?
03-10-2014, 08:09 PM
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What is the ideal air fuel ratios? What's the idea air fuel ratios for idle constant cruise accelerating and wide open? I appreciate any information.
03-11-2014, 07:53 AM
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My bad half asleep when I posted I have lq4 tv2 cam stock casting head with port and polish fast 92 nick Williams 92 truck maf , lt headers 3 in exhaust th400 swap aeromotive a1000 pump now what kinda air fuel ratios should I be seeing thanks again for the info.
03-11-2014, 03:13 PM
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There's ideal, and there's ideal. Then there's real, and
indicated by the instrument.
Ideal for your friends at the EPA is stoichiometric 14.7:1
for real pure hydrocarbon gas, which you can find hardly
anywhere; E10 bends this slightly lower, idea being they
lean out your car some without you having a say-so.
Ideal for fuel economy is leaner. Lean cruise is not legit
here in the states but some import models like GTOs had
its vestiges intact and enableable. You can fake it a
little by adjusting O2 sensor pivot voltage although this
is likely not too consistent.
Ideal for power is richer, and how much richer depends
on the motor build, boost, power adders and so on.
Stock motors can be happy at 13:1 but as you increase
cylinder filling / scavenging efficiency (H/C/I) this will drop
for a given compression ratio. It also plays off against
spark advance. You can probably find anecdotes from
builds that match yours, if yours is not too kooky. But
that's all they can be, you have to plow that field yourself
and find what optimizes whatever outcome matters most
(track MPH, dyno HP number, stuff not breaking, etc.).
NA is almost certainly above 12.5:1 and below 13:1.
Now aggressive airflow mods, cam especially, can result
in cheap wideband meters (which they all are, compared
to a 4-gas sensor) getting a skewed idea of AFR because
it reads residual exhaust oxygen and computes an AFR
based on some assumptions. One being that intake air
does not get to the exhaust without being part of the
burn. This becomes untrue with a cam that has significant
overlap, and a smaller overlap becomes significant when
you are boosted. This skews readings lean, you will never
know just how much with any accuracy (and how much
will vary with RPM and MAP and who knows what-all).
So tuning to a meter number should be the start, not
the end of optimization.
indicated by the instrument.
Ideal for your friends at the EPA is stoichiometric 14.7:1
for real pure hydrocarbon gas, which you can find hardly
anywhere; E10 bends this slightly lower, idea being they
lean out your car some without you having a say-so.
Ideal for fuel economy is leaner. Lean cruise is not legit
here in the states but some import models like GTOs had
its vestiges intact and enableable. You can fake it a
little by adjusting O2 sensor pivot voltage although this
is likely not too consistent.
Ideal for power is richer, and how much richer depends
on the motor build, boost, power adders and so on.
Stock motors can be happy at 13:1 but as you increase
cylinder filling / scavenging efficiency (H/C/I) this will drop
for a given compression ratio. It also plays off against
spark advance. You can probably find anecdotes from
builds that match yours, if yours is not too kooky. But
that's all they can be, you have to plow that field yourself
and find what optimizes whatever outcome matters most
(track MPH, dyno HP number, stuff not breaking, etc.).
NA is almost certainly above 12.5:1 and below 13:1.
Now aggressive airflow mods, cam especially, can result
in cheap wideband meters (which they all are, compared
to a 4-gas sensor) getting a skewed idea of AFR because
it reads residual exhaust oxygen and computes an AFR
based on some assumptions. One being that intake air
does not get to the exhaust without being part of the
burn. This becomes untrue with a cam that has significant
overlap, and a smaller overlap becomes significant when
you are boosted. This skews readings lean, you will never
know just how much with any accuracy (and how much
will vary with RPM and MAP and who knows what-all).
So tuning to a meter number should be the start, not
the end of optimization.