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On 19 Mar 2003, at 17:17, 13brv3@mchsi.com wrote:
SNIP
>
> My current question, is about oil/water heat exchangers. It
seems
> that I've read where someone tried this, and gave up on it, but I
> can't think of who that was, or how hard they tried to make it
work.
> In other words, did they just try an existing auto trans cooler, or
> did they have something special built. Does anyone know any
> specifics?
>
Hi Rusty,
Funily enough, I have done JUST that with our road going tarmac
rally car. (See attached pic). Over on the left guard you will see a
big rectangular box. That houses a bar & plate oil/water heat
exchanger.
This was proof of concept - the car is currently in bits and the body
is at the 'beaters getting IMSA flare kit and a new [paint job. The
plumbing will all be done in braided SpeedFlow hose and fittings
when re-assembled. (The photo shows it with cobbled together with
ordinary rubber hose and ends).
It is also getting an FD engine and a new inlet manifold and
thpottle body, and 10:1 RX8 rotors. Plan is to mount the heat
exchanger across wise between the radiator the front of the engine.
The mechanical water pump is going and will be replaced by an
EWP. Thenew fibre bonnet will have a duct to vent the cooling iar
from the rad upwards.
The oil/water heat exchanger has it's own separate booster pump
that is actuated at times of prolonged and severe load. It is
necessarily large as the engine puts out 650 BHP at full noise. It
has 2 "V Spec" GTR ball bearing turbos - one per rotor. they spool
up a lot quicker and the is little turbo lag - current rotors are 9.4:1.
I chose this method as mounting 2 separate water & oil heat
exchangers was a pain and quite complicated, especially getting
air through the oil cooler. . It also allowed me to use one HUGE
radiator, and made the ducting a lot simpler. (The car also has a
HUGE Nissan GTR sized bar & plate intercooler down the front) so
air flow and space was at a premium.
Other advantages of water/oil heat exchangers is that the engine
warmup is FAR more rapid, the oil & water always stay at the
same temp (more or less anyway) and particularly in sub zero
early winter mornings (even in Sydney, we often have temps down
to -3 -5 Deg C in Winter - moreover, up in the Blue Mountains and
on the Western Slopes, it has been known to make choir boys
from alloy anthropoid apes!!). Tasmania can be even worse!! And I
can't really have "cowl flaps" (}:>) on a race car!!
So using a properly engineered oil/water heat exchanger allows the
engine to run at it's optimum design temp.(If you use a thermostat
that is!!).
Of course, all of this is either extremely "revisionist", "radical",
"extemist" or "revolutionary' thinking (depending on your current
mind-set). To be sure, it would be "anathema' to SOME+ of the
more influential mathematically challenged rocket scientists of that
"other" place.
However, as I have already been pronounced a heretic, (and a
lunatic!) and suffered the wrath of HIM on more than one occasion,
AND have recently been summarily ex-communicated from the
ACRE communion, further heresy won't matter a damn!.
Now I feel comforted in knowing that we have a "broad church"
here, that will tolerate other heretical ideas like "Plugs Up" and
EWPs, so I feel safe from any inquisition of latter day
Troquemadas. So I shall expound the new doctrine and see if I can
pick up a few proselytes!! (}:>)
My current (laternal) thinking for aircraft use is to use an
evaporator core IN the sump (custom made of course), and run the
oil OVER the outside of it (where the air normally goes - this will
also assist in de-aerating the oil). This has the added advantage
of acting as a baffle to discourage oil surge in the sump. The water
is then run THROUGH the evap cooler where the gas normally
goes.
Now this means that you only need external WATER heat
exchanger(s), and there is no need for 70 -90 PSI hi pressure oil
lines running all over the engine bay to burst, spray oil everywhere,
and catch fire (I keep on thinking of poor Chuck Halbert and his
Velocity problems - part of this idea was in response to Chuck's
experiences).
So one simple pressure PIPE from the font cover to the back
housing is all that is necessary. It also cuts down on the number
of sharp bends and fittings which also add to the oil temp.
(Somebody pointed that out some time ago - the racers always try
to use smooth fittings, not banjo bolts - every 90 degree bend
causse tutbulence, and creats heat and a pressure drop).
For sure, it does mean that the water radiator(s) must be bigger
in capacity to reject ALL the engine heat, but is NO bigger than
the COMBINED area of the water and oil coolers together..
Have a look at the Series III ('83 - '85) RX7 setup. They have a full
length rad and a small oil'water unit between the back housing filter
mount and the filter. Works a dream (at least on a road car). I
have one on my "mule', and my good lady June's car as well (It's a
series I '79 model brought up to later specs with an '89 NA engine).
Anyway, have a careful think about this.. As always, I'm happy to
accept peer review, and if my ideas are indeed "beyond the Pale',
I shall always be ready to recant and seek absolution from my
fellow experimenters!
Cheers all,
Leon
Best Wishes & Kindest Regards,
Leon Promet
Aerota.com
leon@aerota.com
0408 223 675
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