Supercharger performance kit pulls 300+ horsepower from Kawasaki jet ski


July 31, 2007

Riva Racing's supercharger kit for the STX-15F turns the stock jet-ski into a race-ready, 300+hp monster.

Riva Racing's supercharger kit for the STX-15F turns the stock jet-ski into a race-ready, 300+hp monster.

July 31, 2007 Any jet-ski boasting a stroked-out, 1500cc motor straight from the Kawasaki Ninja ZX-12R should be treated with extreme caution – but since the 250-horsepower Jet Ski Ultra 250X was released, owners of the STX-15F have been feeling a little left behind. Not to worry – nothing succeeds like excess in the petrol head world, and the aftermarket has stepped in with a bolt-on supercharger capable of turning the STX-15F into a 330-horsepower aquatic widow-maker that can launch you and a horrified passenger to 60mph nearly as fast as a road-going superbike, leaving your 250X-riding buddies gasping in your wake.

Riva Racing’s supercharger system for the Kawasaki STX-15F is a full kit including all necessary engine components to pimp out a stock 60mph STX-15F into a race-ready, 80mph closed course shoulder-dislocating monster. It contains the same specifications that Team Kawasaki won back-to-back Pro Runabout World Titles with, producing over 300hp using VP MS109 race fuel (Jet X).

That obscene horsepower figure only has to pull a weight of 337kg, putting the beefed-up STX-15F very close to a 1hp per kilogram power-to-weight ratio that’s up there with fire-breathing superbikes like Yamaha’s R1 and Suzuki’s GSX-R1000. It won’t do the 0-60mph sprint quite as quickly as the bikes – water doesn’t hook up like tyres on tarmac, but we’re still talking low 3-second bracket times.

A Vortech R-5 belt-driven centrifugal supercharger is the heart of the mod kit, which also includes forged racing pistons, bigger injectors, an auxiliary fuel pump, auxiliary fuel pressure regulator and a base gasket spacer. Pressurized air from the supercharger is cooled through a water-cooled intercooler before being forced into the original throttle body and a boost of 13lbs pumps up the stock motor’s original peak output by around 100%.

A free-flow exhaust lets the engine breathe more freely while unleashing a throaty roar, and the intake grate and ride plates are also replaced to improve hook-up and handling. The main pump and impeller are replaced with beefier items for maximum acceleration and there’s several other mods included to make the jet ski handle more like a racer too.

Riva recommend the kit for closed course racing only – and it’s certainly priced for the professional at a total price of US$10,568. For your dollar though, you’re buying a very pure adrenaline hit… if you have the guts to open the throttle!

About the Author
Loz Blain Loz has been one of Gizmag's most versatile contributors since 2007. Joining the team as a motorcycle specialist, he has since covered everything from medical and military technology to aeronautics, music gear and historical artefacts. Since 2010 he's branched out into photography, video and audio production, and he remains the only Gizmag contributor willing to put his name to a sex toy review. A singer by night, he's often on the road with his a cappella band Suade. All articles by Loz Blain
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