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Why
are the cooling and lubrication systems so
important in air-cooled
engines?
Air-cooled engines run hotter than their equivalent
liquid-cooled engines.
Doesn't
all the heat from the combustion process go toward
producing power?
No. The internal-combustion engine is terribly
inefficient. Of the 100% available heat produced,
about 25% is lost to the cooling system and 40% to
the exhaust system.
How
hot are exhaust
gases?
Exhaust gas temperatures are approximately
1200ºF (650ºC) at the exhaust port.
Turbocharged, supercharged and modified engines can
be as much as 200ºF (93ºC) hotter.
Increased horsepower produces more heat. Excess
heat reduces component life.
How
does this affect the
engine?
In the 911 engine, the exhaust system (containing
high temperature exhaust gases), runs along the
bottom of the engine. The heat radiating off the
pipes heats up adjacent engine parts adding to the
heat the cooling system must reject.
Porsche heat exchangers provide efficient exhaust
scavenging but also create a large surface area for
radiant heat.
How
hot does this area get?
Exhaust pipes
are approximately 1.5-2" from the lower valve
cover.
Exhaust pipe temperature next to the valve cover is
approximately 600ºF. At sustained,
full-throttle conditions, the heat from the exhaust
can be hot enough to melt spark plug wires on twin
plug ignitions.
My
oil temperature goes up to and 250ºF
(121ºC) on occasion. Will
HEETSHEET™lower the oil
temperature?
HeetSheet
increases the cooling reserve by reducing high
temperatures in this area of the engine. The entire
cooling system plays an important role in
controlling overall engine temperatures.
If the engine is experiencing high oil
temperatures, you may be overloading the engine or
additional cooling capacity may be needed (e.g.
additional or larger oil coolers). You should
consult with an experienced technician if your
vehicle is overheating.
Driving habits also affect running temperatures.
For example, stop and go driving increases heat
buildup due to reduced air flow under the engine.
Full-throttle driving also increases the load on an
engine.
How
effective is HEETSHEET™in reducing
exhaust radiant
heat?
Our test engine running an oil temperature of
220ºF (104ºC) displayed a peak
temperature of 300+ºF (150ºC) at the
valve cover (as measured by a Thermax temperature
sensor, as shown). 911's with thermal reactors
('75-'76) run much hotter exhaust temperatures.
Click on the picture at left for the latest test
results.
After installing the shield, the heat sensor
displays a peak temperature of 220ºF
(104ºC). That's a reduction of 80ºF
(45ºC)! Temperature reduction in this area of
the engine increases the engine's safety
margin.
My
oil temperature never goes higher than 220º
(104ºC). Why do I need
HeetSheets?
The oil temperature gauge displays the average oil
temperature from all parts of the engine. Some
areas run much hotter than other areas, and high
temperature radiant heat from the exhaust pipes
increases localized engine and oil temperatures.
Excessive temperature in this area decreases the
life of valve guides and valve guide seals.
If heat shields are so effective, why didn't the
factory use them
originally?
Engineers attempt to foresee the conditions their
vehicles will operate. Being human, their educated
forecasts are not always on the mark otherwise
their cars would not have any problems at all.
Porsche did not foresee the wide variation in
climate, ambient temperature and altitude in which
we operate our cars. They experienced the same
oversight when designing the A/C system; okay for
local climates; less successful in US markets, or
not supplying external oil coolers on cars shipped
to the U.S.
Shown is a factory GT2 racing engine (about 1998
vintage) with a factory heat shield mounted on the
valve cover to deflect the enormous heat from the
turbocharger installed nearby. Early turbo engines
run do not use a shield. These are good candidates
for HeetSheets.
Will
HeetSheet fit my 930
Turbo?
Yes. HeetSheets are especially valuable for these
engines as the peak exhaust temperatures are at
least 200ºF higher (here's
one example).
I've
got a 993 (3.6 liter engine). Will the HeetSheets
fit?
Yes. We now have a 3.6 hardware kit that
allows these engines to benefit from the
HeetSheets. An added benefit is the protection for
the lower spark plug wires that tend to melt
without a shield. The valve covers on 3.6 engines
use either an M6 bolt or an M6 stud.
Let us know which type you have.
How
long does it take to
install?
About 5 minutes. each side. HeetSheets mount easily
on the lower valve cover. Included are
corrosion-resistant, stainless steel and yellow
zinc-plated fasteners and hardware.
My
Exhaust System Is Modified. How Can I Verify It's
Going To Fit?
Here's a rule of thumb fitment:
HeetSheet installation requires approximately 1.25"
(32mm) of clear space in front of the lower valve
cover. HeetSheets will fit if this minimum space is
available. See the illustration on the left.
Minimum space required for installation
(view from rear of engine):
How
can I purchase
HeetSheets?
(click
here)
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Custom race car exhaust system
Click on picture for before and after results
Factory heat shield on GT2 race engine.
HeetSheet installed
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