Miata Mailing List: June 1997, Message #233
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From: "Fletcher Blades" <fblades@fanshawe.newzealand.ncr.com> Subject: Re:Air temp measurements. Date: Tue, 3 Jun 1997 01:38:47 -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 Yes, #1 was quite small, but very repeatable, I did it 4 or 5 times, and the thermometer would start drifting as soon as the lights changed position (and I always gave it enough time to settle). I honestly did not expect it to make any difference at all, and nearly didn't bother testing that configuration. The 60 km speed may have been 4th or 5th gear, I don't remember, 100Km was definitely fifth gear so thats around 3500 rpm or so. (isnt it? oh no, now I'm doubting my memory) Fletch.