[DeTomaso] New Rear Window and Engine-Bay Cooling Fan

Asa Jay Laughton asajay at asajay.com
Sun Oct 2 01:19:33 EDT 2016

   I would like to see more photos, outdoors sitting alongside other
   But with that said and only seeing the two photos you have in your
   gallery, my opinion has changed.  I had my doubts that it would look
   significantly different, but I must say that I think adding the rear
   window easily adds a few thousand dollars to the car's appeal.
   Honestly, I think it gives it a really nice clean look.  It -does- look
   like it's meant to be there.
   You did a great job of engineering to make it work.  I'm anxious to
   read the article.
   Asa  Jay
Asa Jay Laughton - W7TSC, MSgt, USAFR, Retired
& Shelley Marie
Spokane, WA

   On 10/1/2016 8:11 PM, Stephen wrote:

   For some time I have been thinking about installing a window in the
   opening behind 5332's engine compartment.  Originally there was meant
   to be glass in the opening, but, according to Tom Tjaarda, there were
   overheating issues and the window glass was left out.

   I decided to firstly see what would happen with the opening blocked off
   and the car idling.  One 70 degree F day I blocked the opening and let
   the car idle while I monitored the inlet air temperature via the remote
   for my MSD fuel injection.  With a hot engine and a 70 degree ambient
   air temperature I saw the inlet air temperature go up at a rate of
   roughly a degree Fahrenheit every 2 seconds.  I quit the experiment
   when the inlet air temperature hit 150F.  As an aside, I had previously
   noted when I was stuck in traffic on a hot day that the FI would get
   finicky if I sat long enough.  I figured the issue was excess
   temperatures even with the opening behind the engine open.

   Clearly it will get right hot in the engine compartment if one blocks
   off the opening.

   Earlier this year I did a series of tests to see how significant the
   air flow was through the opening at speed.  My testing showed the air
   flow through the opening was around 20 to 25 feet per second (14 to 17
   mph) at a road-speeds of 60 to 80 mph.  The flow through the opening
   equates to an air volume of around 2000 cfm at 70 mph.  If I installed
   glass in the opening I figured I needed to install a fan to provide a
   reasonable flow to keep the engine compartment from overheating -
   somewhere around the air flow rate when the car is going 30 mph -
   around 800 CFM.

   So, given I intended to install a window in the opening to keep from
   pulling water and dirt and rocks and grass and whatever is on the road
   up onto the engine when driving at speed, as well as to keep folks from
   being able to reach in and take whatever they wanted off the top of the
   engine, I figured the first step was to figure out how to keep the
   engine compartment cool.

   Looking at SPAL radiator fans - wow - even a 10" low profile fan puts
   out 800 cfm.  I thought this would be sufficient.

   Next I looked below the car to see where I could hide a fan.  Turns out
   there is a great space below the coolant surge and swirl tanks - just
   behind the bulkhead and above the frame rails.  Measurements suggested
   that a 10" fan would fit.

   Next - how to keep dirt and rocks and leaves and the like from getting
   thrown up into the fan.  I did an online search for 12 inch circular
   screens and found a rather novel solution - 12" stainless steel flour
   sieves.  Talk about a slick fit - check out this picture:
   wzjK . You can see two of the angle brackets I used to mount the
   fan/shroud to the frame rail and inner sill.  There is one additional
   bracket that mounts to the frame rail.  When mounted, as shown in the
   next 3 pictures in the above gallery, it is very solid and out of the

   I set up a SPAL PWM (pulse width modulated) fan controller with a
   Derale 16760 Push-in Radiator Probe to control the fan speed.  I like
   the PWM controllers - they ramp up fan speed as the temperature goes
   above the temperature you choose as your lower target.  Then, if the
   temperature continues to go up, the fan is at its maximum speed when
   the temperature hits your upper target.  If you have a second fan, it
   will turn on when the temperature hits your upper target.  I use one of
   these on the radiator fans for 5332 and on the fans for our '69 XKE.

   I mounted the temperature sensor to the fuel line going to the FI
   throttle body and set the controller to start spinning the fan at 140F,
   with an upper limit of 150F, whereupon the fan is spinning at full

   With the opening blocked, the fan, at full speed, brings the inlet air
   temperature to the FI system down at about 2 degrees per second.
   Worked like a charm!

   After installing the new rear window Kels and I joined the PNW Pantera
   Group for a run up into British Columbia - going to a car show in
   Nelson.  Logged around 1200 miles on that trip:  The fan only came on
   once - when we restarted the car after letting it sit for 30 minutes
   while we were in a store.  Fan came on, temperature dropped and it shut
   off within 30 seconds.

   When driving at speeds over 10 mph with the rear window in place the
   inlet air temperature held around 40 degrees F above ambient.  This
   jives with what James Fusco told me - he explained that "the air that
   comes into the engine compartment has already gone through the radiator
   and along the bottom of the car".  OK - that makes sense.  And, it is
   apparent that, even at fairly low speeds, there is a lot of turbulence
   in the engine compartment, which keeps the compartments temperatures as
   cool as could be expected, given that the air is coming from below the
   car/the radiator.

   Fortunately I mounted the engine-compartment cooling fan to one side of
   the engine compartment - turning it on at speed does cool the inlet air
   temperature.  And, when sitting still, the fan is very effective since
   it is likely drawing air that has not been through the radiator.

   The fan blows air up the passenger side of the engine, across the top
   of the engine compartment, and down the other side.

   I've included a couple of pictures of the installed window in the above
   referenced photo gallery, along with some pictures that I will discuss
   when I put together an article for the newsletter.   There are
   definitely some challenges to getting the rubber around the window laid
   in nicely - I will cover those in the article.

   I think the rear window finishes the look of the car - it is surprising
   to me how much more complete it makes the back of the car look.  And,
   before anyone howls about modifying the car - well, hmmm - it was
   originally intended to be there - except there was no provision for
   letting the engine compartment vent hot air when sitting still.

   Stephen Nelson


   1. [4]http://www.snclocks.com/TheRestofourWorld/Autos/Technical-Bits/i-mN7wzj


Detomaso Email List is not managed by POCA
Posted emails must not exceed 1.5 Megabytes
DeTomaso mailing list
[5]DeTomaso at server.detomasolist.com

To manage your subscription (change email address, unsubscribe, etc.) use the li
nks above.

Members who post to this list grant license to the list to forward any message p
osted here to all past, current, or future members of the list. They also grant
the list owner permission to maintain an archive or approve the archiving of lis
t messages.

No virus found in this message.
Checked by AVG - [7]www.avg.com
Version: 2016.0.7797 / Virus Database: 4656/13127 - Release Date: 10/01/16


   1. http://w7tsc.org/
   2. http://www.teampanteraracing.com/
   3. http://www.snclocks.com/TheRestofourWorld/Autos/Technical-Bits/i-mN7
   4. http://www.snclocks.com/TheRestofourWorld/Autos/Technical-Bits/i-mN7wzjK
   5. mailto:DeTomaso at server.detomasolist.com
   6. http://server.detomasolist.com/mailman/listinfo/detomaso
   7. http://www.avg.com/

More information about the DeTomaso mailing list