Turbocharging: Honda Engineers Harness the Laws of Physics

In 2002, Honda introduced the exciting concept of turbocharged four-stroke engines to the PWC market in the form of the AquaTrax F-12X. This abundance of force-fed power was a revelation to the three-seater class, and once enthusiasts got a taste of how sweet this extra power could be, the call went out for more of the same. Now for 2003, Honda brings turbocharging to the two-passenger class in the form of the innovative AquaTrax R-12X.

Why turbocharging? Fundamentally speaking, internal combustion engines are air pumps. An air/fuel charge is drawn into the engine cylinder(s), compressed and ignited in the cylinder head, and then is released out of the exhaust system. The amount of power produced by an internal combustion engine is dependent upon the amount of air drawn in and retained in the cylinders. Given this sequence, the power an engine is able to produce at any given rpm will increase proportionally with displacement gains; a bigger engine yields bigger power.

This engineering principle remains constant, for the most part, because the atmospheric pressure of the air surrounding us at sea level remains at about 15 pounds per square inch (psi). As a result, that 15 psi is the highest degree of natural pressure available to feed the air/fuel mixture into an engine's cylinders, which means each cubic inch of engine displacement can only yield so much power. The sole exception to this constant is a negative one; air pressure falls slightly as elevation increases, which accounts for the loss of power an engine undergoes when operated on a mountain road or a high-elevation lake, for instance.

Turbochargers vs. Superchargers

Pressurizing the fuel intake system of an engine has become a time-proven method of generating additional power from an engine of given displacement. As would be expected, using a forced-induction system to pack extra air/fuel mixture into an engine's cylinders at a pressure greater than the atmosphere's 15 psi results in a direct increase in power. Fundamentally speaking, there are two ways to accomplish this task: turbocharging and supercharging.

A supercharger requires a drive system for operation. Typically, this is some sort of gear- or belt-driven arrangement that takes its power from the crankshaft and adds weight. Unfortunately, the supercharger and its drive mechanism consume power from the engine with the added mechanical friction of these components.

A turbocharger, on the other hand, is free of the complex mechanical linkages necessary to drive a supercharger, because it uses a portion of the engine's exhaust energy--which is usually wasted energy--to spin a turbine coupled to a centrifugal compressor. The compressor, in turn, forces the air/fuel mixture into the engine under elevated pressure, and combustion of this denser fuel charge generates an increase in power compared to a normally aspirated engine of equal displacement. Moreover, the power-producing characteristics of a turbocharger are naturally suited to a waterjet pump, because a turbo tends to avoid cavitation while building power--an Achilles heel for superchargers. An additional bonus of the turbocharger are lower exhaust noise levels, as wasted exhaust gas and the inherent noise from the exhaust are diverted into combustion chamber pressurization.

In summary, the advantages of turbocharged engines are: increased output without increasing engine speed or displacement; less friction and simplified drive compared to a supercharger without a parasitic power loss; greater power-to-engine-weight ratios; and lower exhaust noise levels.

In the case of Honda's AquaTrax R-12X, the turbocharged 1235cc engine also incorporates an intercooler to cool the pressurized air. The intercooler is an open-loop, ambient water temperature cooler that lowers the air temperature in the air intake tract just prior to the fuel-injected throttle bodies. This cooling action increases the density of the air, and with this increased density comes even more power during the combustion cycle.

Extra Power Plus Extra Durability

In order to cope with the higher loads that are a result of the R-12X's elevated power output, Honda has equipped the R-12X with high-performance, durable forged connecting rods and pistons. In addition, a cooling jet of engine oil is sprayed continuously on the underside of each piston, which helps keep engine temperatures in check.

Because this turbocharger was developed specifically for marine duty, the turbine housing is made of ni-resist cast iron, a material known for its ability to resist corrosion. The turbocharger compressor is lubricated by filtered oil and is additionally water cooled. The turbocharger's water jacket housing is equipped with its own anode to prevent corrosion when used in sea water.

Around the world, the name Honda is synonymous with racing dominance, supreme quality, daring innovation and enviable reliability. Now, the two-seat high-performance muscle-craft class of personal watercraft will enjoy the same qualities in the form of the turbocharged AquaTrax R-12X.

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