Alex Harris wrote:
> I have more questions about this, please bear with me here... :-)
Keep the questions coming Alex - don't just agree w/the majority - prove it to
yourself.
> OK, our performance suffers when the intake air gets too warm. As I
> understand it, the warmer the intake air temperature, the less oxygen
> actually gets into our engines (because air expands as it gets warmer).
I agree that is generally true because the oxygen molecules are spread out more
in hotter temps. Closer together (and thus more dense) in cooler temps.
> Evidently, now we can compensate somewhat with the IAT adjuster, setting the
> PCM input so it thinks it's cooler than it really is. But if the problem is
> that we're not getting enough air, how does fooling the PCM into thinking
> we're getting more air help?
In my opinion - it doesn't help. Remember more air means more fuel. If you
fool the computer into thinking the air is cooler - it will just add more fuel
to "compensate". Since the factory calibrations (even in the MP computer) are
overly rich, going richer will only make things worse (except maybe on heavily
modded engines).
> Does this mean that our computer isn't doing a
> good job setting the A/F ratio for maximum efficiency
Using feedback from the O2 sensor (typical control system), the computer will
keep the A/F ratio at or near 14.7 to 1 regardless what you change (within
limits of course). This is true during closed-loop control mode (90+ percent of
vehicle operation). Only during open-loop control (jamming on accel, or WOT)
will it revert to the built in tables. And remember - those are the overly rich
ones - again, no help by going richer.
> One final question... if our engine has a temperature "setting" where it
> runs its best, why do we have an IAT at all?
The engine block/coolant temp is the one that everyone (even Mopar Muscle and
Mopar Performance) says is optimal around 182 degrees - not really related
here. The IAT is there because the fuel delivery system must work in a wide
range of intake air temps. It is basically part of the formula for calculating
the fuel requirements at any given air intake temp, load, etc. This is how a
MAP-based EFI setup works (as opposed to measuring it directly via a MAF
meter). I posted a formula to the DML one time but am having trouble finding it
now - time to do some searching...
Latr,
Shane
-- '96 IndyRam-HisIndy-MPI/TB/Pulleys/AccelCoil/MPComp/HookerSuperComps/CompTAs '96 IndyRam-HerIndy-numbered(#142)"Track Truck" '74 Triple-Black Dodge Challenger Rallye 360 home-brew EFI R&D vehicle '68 Black Corvette Convertible 427 (For Sale)
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