hi all,
back in the 70's, we used a manometer to measure pressure under the hood of
a tiger at various speeds in various locations.
what we found was that air becomes trapped inside the engine compartment as
you whiz along the highway.
to allow it to escape, the factory put vents in the sides of the rally cars,
and some guys put vents in the hoods, either at the rear corners (like the
LAT hood), or directly over the exhaust manifolds.
these areas correspond to the highest pressure areas under the hood.
raising the hood in the rear is not a good idea, since the base of the
windshield is also a high pressure area, and blocks air outflow from the
engine compartment.
the 260 type open impellor can cavitate at speed, causing a lowering of
efficiency of the pump, and more overheating! the enclosed impellor used in
the 289 302 works better.
we found low speed op to be very nearly a different problem. flow through
the tiny matrix was a major factor, not outflow of air (so much).
thus, the Volvo fan, aluminum radiators, vents, etc. came to be major
upgrades on the cars.
not to mention the low viscosity waterless coolant that boils at 375 degrees
at zero pressure!!
these cars are very under-developed, and as long as you accept that fact,
you will be happy.
Best,
Ray
----- Original Message -----
From: "Thomas Witt" <atwittsend@verizon.net>
To: <tigers@autox.team.net>
Sent: Thursday, July 02, 2009 12:09 PM
Subject: Re: [Tigers] SUNI (overheating)
>>>> Stewart makes a replacement high-flow water pump that should fit the
>>>> Tiger - I might end up installing one of these to make sure there is
>>>> enough water movement.<<<
>
> I remember a similar discussion on the list years ago. The basic premise
> was, "while you are moving the heat away from the engine faster you were
> also moving it faster through the radiator. Thus, with the high flow rate
> the possibility existed that the radiator would not dissipate the heat
> fast enough and the returning fluid would not have been sufficiently
> cooled."
>
> Is it possible to purchase a more efficient radiator (and high flow water
> pump) and then negate the radiator by moving the fluid through it too
> fast???
>
> While I'm sure there is a threshold to a minimum and maximum flow rate it
> seems an efficient radiator (which often equates to larger) becomes the
> deciding factor. I would assume just about any water pump falls somewhere
> between the min/max points. Likely though there are pumps that might be
> better at low RPM cooling than at high RPM and visa/versa. Additionally,
> if one factors in the restriction of the thermostat does it become the
> equivalent of the "NASCAR restrictor plate" and negate a high flow pump???
> There are so many things to factor in.
>
> It would make a great science fair experiment to test radiator in and out
> temperatures relating to flow rate. It seems that a minimal temperature
> change, - yet one that keeps the overall temperature near ideal (180?)
> would be the desired "sweet spot."
>
> Anyway, I'm not trying to make a statement. Rather I'm throwing some
> things out there as food for thought. With all the other contributing
> aspects of the Tiger cooling issues - who knows?
> Tom
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