Miata Mailing List: June 1997, Message #197
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From: 	Erik Christiansen <echrist@phoenix.Princeton.EDU>

Subject: Re: Air intake temp measurements.

Date: 	Mon, 2 Jun 1997 21:14:12 -0500







> All with an ambient temperature of a cool 14C (57F),

> 

> With the probe about four inches into the standard intake snorkel....

> 

> 			at 60 kmh  (37 mph)	at 100 kmh (62 mph)

> 

> Lights down		40 C   	  (104 F)	30 C	  (86 F)

> 

> Lights up		30 C	  (86 F)		23 C	  (73 F)

> 

> 

> As you can see, a definite improvement with the lights up.

> 

> Now for the interesting results, with the temperature probe above and   

> slightly forward of the radiator, ie. where the JR CAI gets its air   

> from...  (I have a '90 so there is no blanking plate to block this   

> airflow)

> 

> 			at 60 kmh  (37 mph)	at 100 kmh (62 mph)

> 

> Lights down		14.5 C	  (58 F)		16 C	  (61 F)

> 

> Lights up		15 C	  (59 F)		18 C	  (64 F)

> 

> 

> Obviously, much lower temps all round, but ;

> 

> 1) the temp is higher with the lights up, opposite of what you would   

> expect.

> 

> 2) the temperature rises with speed, where-as with the standard intake,   

> temp falls with speed

> 

> I am guessing that #1 happens because of swirling under the hood,   

> changing the air flow, possibly slow ing it, or blowing hot underhood air   

> forwards.  This of course woudn't affect the CAI, as the ducting would   

> separate the airflow in from the underhood air, and so they wouldn't   

> affect eachother.

> 

> But #2 is counter-intuitive  (well at least to me).  Anyone got any   

> ideas?  is it just the same effect as #1? or is something else going on?



	Hmmm, my guess would be that the temperature at this location

would rise with vehicle speed as the air is brought to near stagnation

from higher velocities.  (The directed kinetic energy of the particles -

flow velocity - is redistributed as random kinetic energy - temperature).

Picture the car stationairy in a wind tunnel, or better yet the space

shuttle upon re-entry. Of course this ignores heat transfer from the

radiator and engine.  #1 seems interesting.  But the temperature

difference is very small, so it's hard to really say. 

	As for the first set of data, what was the r.p.m. at these speeds.

I would suspect the temperature here would decrease with greater engine

speed, and should be a rather weak function of vehicle speed. 

	Just some thoughts,



		-Erik