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

Effie Richards erichards at zogob.sdcoxmail.com
Sat Oct 1 23:57:49 EDT 2016

You are a genius! I'm printing this for my husband and looking forward to your article in the Newsletter! Bravo!

Sent from Effie's iPhone

> On Oct 1, 2016, at 8:11 PM, Stephen <steve at snclocks.com> 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:
>   [1]http://www.snclocks.com/TheRestofourWorld/Autos/Technical-Bits/i-mN7
>   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
>   way.
>   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
>   speed.
>   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
> References
>   1. http://www.snclocks.com/TheRestofourWorld/Autos/Technical-Bits/i-mN7wzjK
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