FOREWORDThe Boyesen name has been synonymous with racing and perfor-mance 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 contin-ues to thrive in memory of its late founder, who left behind a model of progression and a foundation of innovation. In celebra-tion 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.

ENGINE COOLING DECODED

FROM THE ARCHIVES OF EYVIND BOYESEN

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01MOTOCROSS AIR-COOLED ENGINES of the 1970s relied on a con-tinuous 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 depen-dent 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 manufac-turers. In a time where motorcycle design was seeing rapid im-provements 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,

making possible the beginnings of the potent and durable high-performance off-road engines that we ride currently.

Almost overnight, the advantage of increased compression ra-tios, 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.

THE LIQUID-COOLED ADVANTAGE

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02

THE LIQUID-COOLED ENGINES of the 1980s were built to gen-erate 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 be-comes 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 back-seat to the more complicated task of custom-tailoring horse-power 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 “main-taining 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.

THE MORE THINGS CHANGE, THE MORE THEY STAY THE SAME

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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, en-gines 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, cool-ing 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 dam-age 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 de-signed 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 prema-ture 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 cyl-inder, 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 sys-tem 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 cyl-inder bores, potential damage to pistons and rings, and damaged valve-train components.

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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 un-checked. Several indicators of detonation consist of aluminum coloring on plug porcelain and a loss in power output. Continu-ing to run your engine while detonation is occurring produces excessively high cylinder pressures often leading to mechani-cal damage of parts exposed to these high-temperature/high-pressure 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 detona-tion problem persists, the hammer-like blows could damage the rings, pistons, or rod bearings. Melted pistons come from deto-nation 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.

GAINING CONTROL OVER INTERNAL ENGINE TEMPERATURE

TYPICAL COMPONENT DAMAGE CAUSED BY EXCESSIVE ENGINE HEAT

HOW TO STOP OVERHEATING

04 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.

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.

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