RE: Intake Air Temperature

Subject: RE: Intake Air Temperature
From: Jerry Stadulis <73621.2717@domain.elided>
Date: 20 Sep 96 21:18:54 EDT
Roger Graves wrote:
 
 > Enough! Enough! on this HP/Temperature correction thread... For 
 > those interested, vist the following Web site that includes a 
 > complete SAE conversion program for *all* environmental effects....
 
Thanks for the suggestion, but I did _not_ start this as an HP/Temperature 
correction thread.  It was turned into one because either (a) I didn't state 
my question clearly or (b) Jay and Ruell didn't read the post carefully, and 
jumped to the conclusion that I was saying intake temperature doesn't affect 
HP developed.  I intended this to be a thread about whether the location of 
the intake has an appreciable affect on the intake air temperature.
 
Let me restate my original message.  Our engines are basically air pumps.  
For example, a 2.5 liter engine pulls in about 175 ft3/min of air while 
running at 4000 RPM.  That volume is much larger than the free volume inside 
the engine compartment.  Even if the intake is positioned inside the engine 
compartment (e.g. as with K&N cone-type filters), the pumping action of the 
engine will _quickly_ use up any stagnant air that is inside the engine 
compartment.  The air that reaches an underhood intake therefore comes from 
_outside_ the engine compartment, and should be much closer to _ambient_ air 
temp.
 
My example which showed a 16% density difference between 180 and 80 degree F 
air was _only_ offered to provide an (unrealistically high) upper limit on 
what the intake temp would be if _all_ the intake air were ducted through a 
180-degree-regulated radiator, and ambient temp was 80.  As we all know, there 
are lots of places for ambient-temp air to get into the engine compartment 
besides the path through the radiator.  I _didn't_ imply that a 16% density 
difference was irrelevant to HP developed.
 
_Actual_ intake air temp is used by the engine management computer, so it 
ought to be possible to read it out somehow.  That way someone with an 
underhood intake might be able to compare their intake air temp to an 
OBC-measured ambient temperature, and let us know what the real difference 
tends to be, so we can determine how relevant it _is_ (using Roger's 
reference).
 
And BTW, Ruell, I'm not ignorant, just looking for some real information.
 
 Regards,
 Jerry
 Arlington, TX (20-Sep-96, 20:11)
 '95 540i-6 spd