Engine Cooling Decoded

ENGINE
COOLING
DECODED
FROM THE ARCHIVES OF EYVIND BOYESEN
FOREWORD
The Boyesen name has been synonymous with racing and performance for decades. Eyvind Boyesen’s innovation and development of
reed technology for two-strokes permanently changed the landscape of
motocross performance, and his continued efforts to maximize engine
output in accelerator and water pump design parlayed his legacy
into the four-stroke generation. Today, Boyesen Engineering continues to thrive in memory of its late founder, who left behind a
model of progression and a foundation of innovation. In celebration of the great Eyvind Boyesen, we offer our readers an excerpt
from Boyesen’s personal archives. Not only does Boyesen explicate
a comprehensive evolution of liquid-cooled engines, he illustrates
how cooling affects performance and what can be done to balance
the power of heat and the need to stay cool. After reading, it will
become clear why Boyesen created the Supercooler and why racers
should have one.
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01
THE LIQUID-COOLED ADVANTAGE
MOTOCROSS AIR-COOLED ENGINES of the 1970s relied on a continuous flow of air across the cylinder’s cooling fin surfaces to
control and maintain the internal heat generated by the engine’s
combustion process. The air-cooled process was therefore dependent on the amount of overall surface area that could be used
for disseminating the heat produced by the engine. Because of
this, air-cooled engines had to run relatively lower compression
ratios, thus reducing their potential for higher output levels to be
achieved without sacrificing durability, weight, and overall engine
size in the process. During the early 1980s, rapid technological
enhancements in motocross engine technology would take place
thanks to design innovation coming from the Japanese manufacturers. In a time where motorcycle design was seeing rapid improvements with every year’s model release, it can be argued that
one of the most important advances in off-road performance was
the application of liquid-cooling engine heat-reduction systems.
Machines like the 1981 Suzuki RM 125 and the Yamaha 1982
YZ 125 and 250s first employed production-based water cooling,
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making possible the beginnings of the potent and durable highperformance off-road engines that we ride currently.
Almost overnight, the advantage of increased compression ratios, coupled with more consistent power output and prolonged
durability propelled the liquid-cooling method as superior to the
air-cooled approach. Compared to the advancement of liquid
cooling, air-cooled engines were quite a bit slower, since their
overall horsepower output and their ability to maintain that output
for extended time periods was offset with practicality or engine
size limitations. A liquid-cooled off-road engine proved to be much
more efficient at absorbing engine heat and thus opened the door
to continued development and stronger, more durable engines.
Liquid cooling increased the overall cooling capacity of racing
engines, and as a result of the relatively shorter amount of time
that it took to absorb and transfer heat, the total power output
could be controlled more efficiently. This was and still is a big
deal—arguably even more so with the hotter-running four-stroke
engine designs of today.
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THE MORE THINGS CHANGE, THE MORE THEY STAY THE SAME
THE LIQUID-COOLED ENGINES of the 1980s were built to generate more power as a result of liquid cooling’s substantially
improved ability to absorb and transfer the internal heat that
results from high-performance power output. Fast-forward from
the 1980s to the modern off-road engines of 2013, and it becomes apparent that the same issues engineers and riders both
faced in the ’80s have not changed that much. The inherent
competitive nature of racing dictates two simple and undeniable
truths: riders will get faster, and engines will continually evolve.
Modern four-stroke engines have never been more powerful. In
truth, the tuning efforts of factory teams like Monster Energy
Kawasaki, MotoConcepts, and the Troy Lee Designs/Lucas Oil/
Honda Team focus not on maximum performance output, but
where the power is spread throughout the total operational
range of the engine’s output.
From this perspective, total power output now takes a backseat to the more complicated task of custom-tailoring horsepower to the needs of the rider. This is where an engine’s output
consistency enters strongly into a tuner’s overall performance
parameters. Now more than ever before, the challenges of “maintaining horsepower” and of “controlling internal temperatures”
have come full circle and maintain a connection to the history of
racing engine research and development.
It can be argued that the performance methods of the 1980s
have been largely replaced by a new way of thinking. No longer
is off-road performance tuning solely concerned with increasing
horsepower and torque. Factory teams spend serious time and
money to custom-tailor their engine performance to achieve very
specific power delivery characteristics. In the process, they are
also very concerned with the consistency of how that power is
delivered over the course of a long summer moto. In addition
to horsepower, torque, and the overall power characteristic of
their engines, factory teams and professional performance techs
are becoming more acutely aware of the challenges associated
with managing the enormous heat generated by today’s high rpm,
high-output off-road four-stroke engines.
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BALANCING PERFORMANCE AND ENGINE LONGEVITY
THE ENGINE IN YOUR BIKE, like all internal combustion engines, is a
heat generator. Only by the way of heat can an engine produce power.
The more heat generated, the more power produced. Heat therefore
is a forerunner to racing performance. However, engines are designed
to operate within an “optimal” temperature range. This temperature
range typically spans between 195 and 220 degrees Fahrenheit.
To control the negative rise in operational temperatures, engines use a relatively small amount of cooling fluid because of
the need to keep the weight of your bike as light as possible.
In this regard, the balance between engine performance, cooling capacity, and weight is a very delicate solution—a solution
with a fairly large limitation. For all the exceptional performance
that modern engine designs offer, they do not handle higher
than normal temperatures well and are vulnerable to heat damage when engine temperatures rise beyond optimal operational
range. Because engines rely on their collective working parts to
convert heat into horsepower, much of the heat is attracted by
those same working components. An engine fails if just one part
overheats. Therefore, it is vital that the cooling system keep all
parts at suitably low temperatures. For this reason, when there
is a continuous load on your engine, its cooling system is designed to absorb heat as it builds, balancing the destructive rise
in temperature that occurs at the source. Anytime internal engine
temperatures climb close to or beyond the upper operational
temperature limit, your engine’s horsepower output is reduced.
More importantly, the engine will be running in the danger zone
of overheating, which has proven to be a leading cause of premature wear or critical engine failure of four-stroke engines.
Internal engine heat, although needed for horsepower, is also
extremely destructive to your engine if it is not managed properly.
Internal-combustion engines burn fuel hotter than the melting
temperature of engine materials. When an engine is operating
out-of-balance with its cooling system’s capacity, the internal
temperatures often rise to levels that cause damage to the cylinder, piston, and valve-train components. If these parts become
heated over the optimal operating upper limit range, component
damage will begin to occur. Reduced to its common reasons for
being essential in an internal-combustion engine, cooling system efficiency can have a dramatic influence on the longevity
of the internal working components of your bike’s engine. These
include the reduction of thermal stresses and strains caused by
pre-ignition and detonation (particularly the latter), distorted cylinder bores, potential damage to pistons and rings, and damaged
valve-train components.
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GAINING CONTROL OVER INTERNAL ENGINE TEMPERATURE
THERE’S A FUNDAMENTAL DIFFERENCE between detonation and
pre-ignition. Pre-ignition happens when combustion begins
from a source other than a timed and controlled ignition spark.
It could originate from hot spots in the cylinder.
Detonation, on the other hand, is a form of spontaneous
combustion, brought about by inordinately high temperatures
or pressures in your bike’s cylinder. Even trace detonation, not
evidenced by an audible knocking, can be damaging if left unchecked. Several indicators of detonation consist of aluminum
coloring on plug porcelain and a loss in power output. Continuing to run your engine while detonation is occurring produces
excessively high cylinder pressures often leading to mechanical damage of parts exposed to these high-temperature/highpressure conditions.
If the engine overheats, the first thing that will happen is a
gasoline engine will start to detonate. The engine will ping and
start to lose power under load as the combination of heat and
pressure exceed the octane rating of the fuel. If the detonation problem persists, the hammer-like blows could damage the
rings, pistons, or rod bearings. Melted pistons come from detonation or pre-ignition. Detonation (pinging) is typically caused
by excessively lean fuel-air mixtures or overly advanced ignition
timing of the engine. The “ping” is actually a shock wave that
knocks the protective layer of gas bubbles off of the piston.
With these gone, you then have 1,200-degree combustion temps
directly against aluminum that melts at 800 to 900 degrees,
which is where the hole comes from. Pre-ignition is caused as
the result of an engine having overly advanced ignition timing or
because of accumulated carbon deposits on the piston, head,
or spark plug. These deposits become red hot and ignite the fuel
prior to the spark plug firing. Spark plugs that are way too hot
(heat range) may cause pre-ignition as well.
TYPICAL COMPONENT DAMAGE CAUSED BY EXCESSIVE ENGINE HEAT
Pistons may swell up and scuff or seize in their bores, causing serious engine damage.
Exhaust valve stems may stick or scuff in their guides.
It causes valves to hang open which can damage pistons, valves, seats, and other valve-train components.
04
HOW TO STOP OVERHEATING
Invest in a high-performance water pump system. Hydro-dynamically designed,
the Boyesen Supercooler is your best option.
Use a high-pressure radiator cap to force greater internal coolant pressures.
This will increase flow rates.
Use products like Engine Ice to boost your coolant capacity.
Use a high-octane race gas. Higher-octane gas burns at a slower rate, reducing
the internal engine temperature.
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