why humid is better!

[Ludis Langens]

rahmrh at cableone.net wrote:
> 
> The humidity is not droplets, it is water vapor, and
> the reason that it is bad, is that if you have 14.7psi of
> stuff (or whatever is normal pressure for your location), if
> the pressure of the water vapor is .3 psi, that is .3 psi
> that contains *no* oxygen, whereas the other 14.4 psi
> contains 21% oxygen.

How's this for an explanation (I'm not saying this is correct...):

The intake air is down to 14.4/14.7 of "normal" - the driver
unknowningly opens the throttle a little bit more.  Now the engine gets
as much oxygen as with dry air - plus a little bit of water vapor.  On a
MAF engine (and a carb'ed engine), the results in a higher measured
airflow and hence more fuel is injected.  On a MAP engine, the extra
air/vapor (ie higher pressure) also leads to more fuel.  Presumably
closed loop operation leans out the extra fuel.  However, ignition
timing stays a bit advanced from normal (because of the higher MAF/MAP
reading).  Hence, more butt-o-meter measured power.  The water vapor
acts like water injection and keeps the engine from pinging.

-- 
Ludis Langens                               ludis (at) cruzers (dot) com
Mac, Fiero, & engine controller goodies:  http://www.cruzers.com/~ludis/

----------------------------------------------------------------------------
To unsubscribe from gmecm, send "unsubscribe gmecm" (without the quotes)
in the body of a message (not the subject) to majordomo at lists.diy-efi.org