Home » Features » The new horsepower king – October 16, 2006

The new horsepower king – October 16, 2006

Kawasaki put to rest weeks of speculation in late September by officially unveiling the all-new Ultra 250X, the highest-horsepower production personal watercraft to ever be offered by one of the major OEMs.
Boasting 250 horsepower under its seat, the Ultra surpasses the former horsepower champ, Sea-Doo’s 215hp RXT and GTX Limited, by a solid 35 horsepower, and promises to, if not reignite, at least fan the flames of the horsepower wars of yesteryear.
Air Force
Like Sea-Doo, Kawasaki has found those chart-topping horses with a supercharger, in this case a Roots-style, high-volume, direct-drive blower. A positive-displacement design that does not directly compress air, but rather just moves it at a far faster speed. Roots blowers use counter-rotating lobes to grab outside air and funnel it to the intake manifold. They also pump a fixed amount of air every revolution, rather than rely on increasing rpm.
As such, Roots-style chargers (named for brothers Philander and Francis Roots who patented the design all the way back in 1860) are noted for their ability to develop compression at low engine rpms, which should give the Ultra’s impressive low-end acceleration. They also are relatively simple in overall design, a fact that has given Roots-style blowers a reputation as both reliable and durable workhorses. Kawasaki promises almost instant revs at any speed, from idle to redline. The company also promises a smooth and linear torque curve.
The downside of the process, of course, is the production of power-robbing heat generated by the Kawi turbo’s 11.4psi of compression, a trait that Kawasaki curtails with the addition of a large-capacity intercooler. According to company engineers, the intercooler brings that air back to ambient temperature, or even less. Sea-Doo likewise uses an intercooler on the supercharged GTX models.
Kawasaki’s supercharger is coupled to the existing 1498cc engine shared by the STX-15F, with a few minor tweaks. A lower compression ratio (7.8:1) minimizes detonation at high-boost pressures. Redline also has been increased to 8900 rpm. It’s a package that was already noted for its quick acceleration, and one that should put Kawasaki squarely alongside the best performance machines currently on the market.
To put all that power to the water, the company has designed a completely new 155mm pump and three-blade impeller. A new eight-vane intake guide promises to efficiently feed the water within, providing what the company says is more “traction” than the older-style, six-vane guide. The pump and ride plate both incorporate a lengthwise groove to enhance straight-line stability.
New Hull Design
Unlike recent engine advances that have essentially shared the same hull design, the Ultra also boasts a new hull and deck. Kawasaki reportedly again relied upon its race team’s experience to produce a hull that will ride equally well in calm and rough conditions. Sporting a 22.5-degree, deep-V that likely takes much of the credit for the rough-water capabilities, the Ultra hull also features larger sponsons that were designed to enhance both stability at speed and improve cornering, all while enabling the hull to stay relatively narrow. An upswept bond line, where the hull and deck are bonded together, at the bow also lets the boat penetrate swells with less shock, rather than bounce across the surface. The best part about the hull, however, may be that it was designed to lean into the corners like a motorcycle, allowing both driver and passenger to feel more in tune with the vehicle, rather than fight to stay atop it during aggressive cornering.
As to creature comforts, the Ultra also goes where no Kawasaki has gone before. A five-position handlebar allows both sitting and standing riders to find a comfortable stance atop the boat. Storage and fuel capacity also have been super-sized, with the former topping out at 53 gallons (roughly 20 more gallons than the comparable Sea-Doo GTX Limited), and the latter a whopping 20.6 gallons (again, about 25 percent more than the competition), substantially increasing the boat’s cruising range. A fourth splash deflector also has been added to Kawi’s traditional three-ridge system, to reduce water spray during high-speed turns. Standards like a rev limiter, off-throttle steering and retractable boarding ladder are all in place.
Ultra Lite
Also joining the 2007 lineup will be the Ultra LX, a supercharger-less variation of the Ultra 250X. Aimed more at the recreational, long-range touring crowd, the 160-hp LX shares the same 132.7-inch long, 46.9-inch wide hull design. Coupled with the Ultra’s expansive stowage and fuel capacity, the LX should prove a solid workhorse for touring rides, as well as just a cushy cruiser for the family buyer who doesn’t care to pay the supercharger’s premium price tag. Kawasaki touts the boat as having the longest cruising range of any boat in its class.
Pricing for the new boats has been set at $11,499 for the 250X, and $9,799 for the LX. Kawasaki also returns the STX-15F ($9,499), STX-12F ($7,999) and 800 SX-R standup ($5,999). psb

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