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There was a lot of talking about the performance of the new Kawasaki Ultra 250X when it hit the market, especially about its top speed and its performance around the close course.
It was obvious that the new Kawasaki missile was fast and R&D representatives of the Green Team assured me it was a struggle to keep the top speed to the desirable limit for homologation needs. According to rumors, the 250X reached a top speed of 67+ mph directly out of the box. I had personally tested a preproduction in France, the only one that was available in Europe. In glass water conditions and with an environment temperature of 8° C (46° F) three different riders saw 70mph on the LCD display of the portable GPS.
Last winter the top American aftermarket companies started playing around with the parameters that play key roles to the handling and top speed of this muscle craft – ride plate, intake grate and sponsons. These three parameters, when altered, can completely transform the handing and the total performance of a Runabout.
Two of the most well known aftermarket companies in the US came up with a set of adjustable sponsons, ride plates and intake grates for the Kawasaki Ultra 250X. Both Riva Motorsports and R&D Performance Products USA had to decide if they wanted to appeal to the weekend enthusiast or the demanding racer.
The tests of these products were carried out in three sessions. At the beginning the Ultra 250X was equipped with a Riva ride plate, sponsons and an intake grate. The test was performed in Greece with glass water and choppy conditions. The craft was tested alongside a Limited STX-R (72.9 mph and very good acceleration). Then the test ride team flew to Arizona and made an extensive test ride of R&D’s Kawasaki along with R&D’s tuner Bill Chapin. A third test was carried out in Greece comparing the two packages side by side. The purpose of this test was to find out the differences between the two packages and their orientation.
The Kawasaki that was used in Greece is owned by multi-time national champion Akis Malouchos, owner of Champions Store. The craft was equipped with an aftermarket pump, drop nozzle system, R&D power shot module, block off valves, and an air filter.
R&D – Design features
R&D paid great attention to the design of the sponsons backing plate. According to Chapin, the shape of this backing plate, along with its angle on each side of the hull, plays a significant role in the overall performance of the craft and the straight line stability. The R&D backing plate features three grooves and four steps progressively from the front to rear. The groves’ scope is to minimize the hit of the water on the backing plate. The steps create a low friction, low pressure that relieve the drag within the backing plate channel. The forces act on this heavy muscle craft hull and sponsons especially on high speed or wave jumping are very high, therefore required to be minimized. Additionally each backing plate is made from cast aluminum that is CNC machined precisely to ensure perfect fit and reduce weight. The sponsons are adjustable in two different positions, for recreational (upper position) and race (lower position) use. The R&D design staggers the sponsons blade fins water trapping area to pick up less water in the front and more at the back. The scope behind this concept is to reduce chine walk in high speed corners, while providing more rear end grip. The hard core rider will be able to get more grip and aggressive handling by fitting the new race blades that are designed according to the latest IJSBA regulations.
Riva – Design features
Riva has a different approach to the whole design of the sponsons. The backing plate in made of aluminum, though it is much lighter than the R&D package. It fits in a different position to the hull – similar position and height as the OEM sponsons. The surface underneath is completely straight and it does not feature any steps or groves. The blade itself shares lots of similarities in terms of shape with the R&D ones and it mounts into three positions (high, medium and low). The lower position of the Riva blade has a greater distance from the backing plate and from the same measurement recorded on the R&D. The blade was tested in different positions (back and forth) though both riders decided that the rear hole of the blade was set at two holes from the end at the backing plate. Actually, the Riva blades are adjustable to three positions vertically and horizontally, while the R&D ones can be set in two different positions in a diagonal vertical position.
The actual test
When we first rode the Riva package we were surprised to find that the design of the plate raised the nose of the craft significantly. As a result there was a noticeable increase to its top speed, especially under glassy water conditions. On the other hand, stability was not enhanced to the level we were expecting it to be. In other words, the craft was shaking a bit at the front at top speed and this effect was even more noticeable under slightly choppy conditions. Though it was not enough to make us worry about it, you certainly don’t expect to get such a behavior from an aftermarket bolt-on …and all this just by riding the craft straight.
When we tested the Ultra in a close course environment we realized that the whole Riva package was mainly designed for the weekend warrior rather than the demanding racer. The craft was not turning precisely and as soon as you were exciting the buoy it lifted the nose, making you lose time. This could get even worse if you bolt on the blades to the lower position since the grip was very aggressive, especially when going around the tight turns or hairpins. The harder we were riding the craft the more noticeable was the nose lift.
The R&D package impressed us both when riding the craft in the straight searching for the top speed and on a close course. Straight line stability was not an issue for the R&D set up. High speed cornering was enhanced at all levels without showing any tendency of chine walk. When the blades were placed to the high position the Ultra still hooked up very nicely but it was not very aggressive and tended to forgive the riders’ mistakes; however, the handling is good and straight line stability leaves you with no worries about this set up.
The demanding rider who has good physical condition and can understand the craft’s behavior will not hesitate to mount the R&D blades to the lower position in order to push the craft’s handling to its limits. The rear end of the hull bites hard and provided the needed grip to push the craft harder and harder in every turn. Handling and hook up was predictable with no signs of unexpected rear end slip off or sudden hook up that usually results to a high side. There is no doubt that the R&D intake grate played a key role in the immaculate hook up and superior handling during high or low speed cornering.
Kawasaki Ultra 250X with R&D kit
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