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REFLECTOR: duct installation
In a message dated 1/11/99 2:52:37 PM Pacific Standard Time, firstname.lastname@example.org
> Jerry Brainard wrote:
> > In considering a water cooled engine solution for the XL, I
> > have been thinking about the cooling problem. I have seen
> > examples of counter-flow cooling that are very efficient.
> Counter-flow? Sounds like something interesting to learn about.
There is a kit out that has this avail for the Chevy small block. It was
developed by Smokey Yunick. If anybody was reading Circle Track mag about 9
years ago (June 1990 edition to be exact) they will remember it as "Reverse
Cooling". In a nut shell, the flow is reversed in the block with external
manifolds and modified water pump. On a stock arrangement, the coolest water
leaves the pump and heads for the cylinders where it is pre-heated on the way
to the heads, where the cooling is needed the most. On the reverse flow set-
up, the water goes to the heads FIRST and then the cylinders. This allows
higher compression and leaner running before the heads get too hot and start
the thermal run-away conditions known as pre-ignition and detonation.
> Doesn't the coolant pressure effect the heat exchange?
Smokey Yunick also did some investigation into the use of propylene glycol (as
opposed to ethylene glycol). He found that the prop-gly worked better as it
has a boiling point of 350 F. But it must be PURE. Absolutely any dilution
with water and the boiling point dropped like a rock. He was experimenting
with cooling systems for race cars that would use a thermal syphon flow rather
than a water pump. All this came about because one thing (of several) he noted
in all the years he did engine work, was that at a certain water temp, the
engine started suffering severe problems with detonation. In a race car, with
all of its noise, detonation is never heard but shows up as little balls on
the spark plugs if you're lucky, all the way up to a cracked block. He
postulated something called "particulate boiling". This is the over heating of
the cooling system water that is local to the hot spots in the cylinder head.
The best example would be the area of the exhaust valve seat. The idea is that
the head gets hot enough here that the water boils. When the water boils, it
goes through a state change and absorbs heat. Great! But AFTER it is vapor, it
can no longer absorb the amount of heat needed to keep thermal run-away in
check. The chamber side of the head begins getting hotter and the chances of
detonation goes up greatly when the temp of the charge can't be reduced.
Increasing the pressure in the cooling system is one way to control this, but
is has limits. Most day-to-day cars have 13-14 psi systems. The last model
RX-7 originally had a 21 psi system but that was backed down to 14 psi with a
recall due to things leaking and coolant fires developing on top of the rotor
housing. Race cars can use a 21 psi system if the hoses are good and the water
pump seal is VERY good. That is the limit to current cooling systems: the
water pump seal. When it begins to leak due to over pressurization, the game's
over. That is why Smoket was fooling around with Prop-gly. Because it has such
a higher boiling point, it will reduce particulate boiling without having to
redesign for a higher system pressure. But for some reason, I haven't heard if
it got any farther than the "Gee! What if..." stage.
> Don't thick cores work very well at high velocities?
> In theory at 200 mph we should get lots of cooling right? In practice most
> cooling (water or air) installations I have seen
> don't work properly at high speeds because the air piles up way out in
> of the intake scoop and goes around it. In
> pushers this turbulence is also a prop efficiency problem.
> I only know this from what I have seen funnels do in high speed wind
> They work best with the small end into the
> wind. Maybe some yarn on the plane near our intake scoops could tell us
> something from another airplane close underneath.
> What good is the "correct" size radiator if not much air is going through
When talking to a really good radiator supply house, ask them to explain
pressure drop across the radiator and what value one should shoot for. This is
an excellent indication as to what volume airflow the radiator will work with.
173 RG Gull-Wing