<VV> Engine Bay Air temperature experiment

[kevin nash]

Doc- Thanks for the questions! I have a terrible time thinking how what I write will come across to those who read it, and usually
end up leaving stuff out, and or not being clear enough-in other words I find it hard to anticipate questions that might come up
and answer those!
 
Anyways, yes that rear seal was installed for this test, and yes the probe was remote in the sense that I was reading the temperatures from the drivers seat with the engine lid down the whole time. Not reported in the test, was that I did take some
readings while driving, but that sensor in that placement was reading ambient temperature  nearly the whole time, with the exception being as reported during the morning runs. I agree, it would be good and interesting to see what happens under different conditions and higher heat loads, but I have a hard time doing that around here where I live- there's no freeways,
and I'm breaking the law every time I push it hard enough for long enough to get those elevated engine temps!
 
The reason I became curious about all of this had to do with strange running under certain conditions, usually after it had been
started and run a short while and then shut off again- I began to think that not having that rear seal installed might be causing or making worse a hot soak problem- which it most definitely was, particularly when the damper doors just start to open! The other
reason for the test was that I had noticed that the manifold air temp sensor (located in the cross over tube between the heads and turbo) was reporting considerably higher than ambient temperatures at the end of the same ten mile drive, and it always seemed to coincide with the engine running leaner than I was
after, so I needed to figure out exactly why that was happening and what to do about it. Part of the "why" was to make darn sure
as to what engine compartment "ambient" really was after driving a while.
To make a long story short, I fixed those issues!
Kevin Nash
63 Turbo EFI Daily driver
 
From: RoboMan91324 at aol.com
Date: Fri, 22 May 2015 22:02:04 -0400
Subject: Engine Bay Air temperature experiment
To: virtualvairs at corvair.org; wrokit at hotmail.com






Kevin,
 
Thanks for performing the experiment and for sharing.  I 
have a few questions and comments.  Please don't think of this as "looking 
a gift horse in the mouth."
 
Is it possible for you to perform the same experiment once the 
seal is installed?  Hot air and exhaust exits the engine from beneath and 
the fan will suck that hot air/exhaust into the engine compartment along with 
outside air from above.
 
It doesn't appear so but I don't want to "read between the 
lines" of your description.  Did you by any chance read temperatures or 
have someone read temperatures, remotely while driving?  If not, can you do 
so with your equipment?  If you had to stop, get out and access your 
engine compartment to read the temperatures, you may have irrelevant 
data.  If you stop for a while with the engine off, heat from a hot engine 
will rise up into the engine compartment and heat the air significantly.  
Starting the engine will suck the hot air through the fan and out the bottom but 
I am not sure how quickly that will happen.  Just opening the engine 
compartment lid will change readings quickly.
 
Real temperatures taken while driving under a number of 
scenarios would be best.  The engine generates more heat while loaded 
and at higher RPMs but the fan also sucks more air (CFM) into and through 
the engine compartment at higher RPMs as well.  Even with a hotter engine, 
I suspect the air in the engine compartment will be relatively cool while 
driving at speed.
 
Your unshielded turbo and exhaust tubes in the engine 
compartment will skew your data too.
 
Again, thanks.
 
Doc
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In a message dated 5/22/2015 4:20:22 P.M. Pacific Daylight 
Time, virtualvairs-request at corvair.org writes:
Message: 
  7
Date: Fri, 22 May 2015 16:20:08 -0700
From: kevin nash 
  <wrokit at hotmail.com>
To: "virtualvairs at corvair.org" 
  <virtualvairs at corvair.org>
Subject: <VV> Engine Bay Air 
  temperature experiment
Message-ID: 
  <BAY177-W46596E336F548C48BE4215D3C00 at phx.gbl>
Content-Type: 
  text/plain; charset="iso-8859-1"

I've been fine tuning my EFI set-up 
  recently and was curious as to how hot the engine compartment air was getting 
  while the engine was running during normal cruising. The engine compartment 
  air temperature was a particular concern to me as I don't have a heat shield 
  on the turbo (yet) and, until very recently hadn't bothered to put on the rear 
  engine compartment seal either. Anyways, I thought I remembered someone on 
  this board had asked about engine compartment air temps  sometime ago and 
  I just got done doing the test, I thought I would share my results. Since I 
  was concerned about the air temp just before it enters the air cleaner, I put 
  a digital thermometer probe on top of the throttle body's, not touching any 
  metal, approximately 1" away from the air cleaner. 

Morning before 
  starting engine and driving to work: T= 53F, 10 miles later, T=67F, head 
  temperature was well below 300. Afternoon before starting engine and driving 
  home: T=83F. stopped at gas station to get gas after 2 or 3 minutes of 
  running- right after re-starting the car, T=97F. Continue on home, head 
  temperature gets to 300 degrees, and the digital thermometer reads.... 
  82F.  I've done this same test 2 days in a row now, and have gotten the 
  same results each day, and I also verified that the digital thermometer agrees 
  well (within 1 degree) at 52F and 70F with our outdoor 
  thermometer.
For curiosity's sake only!!
Kevin Nash
63 Turbo, 
  EFI daily driver