What is a supercharged jet ski?

If you listen carefully, that jet ski’s engine will have a bit of a whine to it. That’s because it is tapping into a big performance kick from a device called a supercharger.

The engines in most jet skis are normally aspirated, meaning they suck in air at atmospheric pressure, mix it with precise amounts of fuel, and use that to power an impeller that sucks in water and shoots it out of the back of the ski at high pressure.

But superchargers act like a bicycle pump to force air into the engine. More air, mixed with precise amounts of more fuel delivered via modern-day fuel injection systems, delivers more performance.

Superchargers have been around cars for around a century, so it’s no surprise that they’ve made their way into the jet ski world. They help the engine produce significantly more power from low in the rev range, making them perfect for helping a jet ski up onto the plane.

A supercharged jet ski’s performance is pretty exhilarating compared with a normally aspirated one. 

The way superchargers force air into the engine can vary. The two common types are turbine superchargers – sort of like a mechanically rather than exhaust-driven turbocharger – and screw superchargers using meshed screws to pump air. 

Superchargers spin at around 50,000rpm to work effectively.

The way the supercharger is integrated into the engine varies between the brands. For instance, Kawasaki turns its screw supercharger using a toothed belt. In contrast, Yamaha and Sea-Doo use a centrifugal clutch to turn their turbine superchargers.

The difference between the two comes down to what happens when they break; the Kawasaki will lose power as soon as the belt breaks, but the clutch-driven system will still operate, albeit with a big hit to performance. 

There could also be a big difference in the amount of damage they do when the supercharger’s drive systems break; a belt will just fall off, while a failed clutch could eject bits of metal all over the place.

Maintenance is the key. It’s important to replace supercharger drive belts and change the oil on a clutch-driven supercharger regularly.

One of the issues with compressing air is that it produces heat as a byproduct. That’s why many superchargers are fitted with intercoolers, a sort of radiator for the supercharger that cools it down using water.

The intercooler is important because if the compressed air heats up too much, the fuel being injected into the cylinder could ignite before the engine’s management system can fire the spark plug to produce the downward power stroke.

This is what is known as “detonation”, where the fuel ignites shortly before the piston reaches the top of the cylinder instead of when it is on the way down. You’ll recognise if you’ve been a victim of detonation because it will instantly wreck an engine, usually accompanied by a loud “bang!”.

Sea-Doo jet skis use a closed-loop cooling system for their engines meaning they do not use the water they ride on to cool down the engine while it is running, relying instead on airflow. Other brands used open-loop cooling systems that suck in water and circulate it through the system.

Jet skis use an open-loop cooling system for their supercharger intercoolers. That means it is important not to over-rev the jet ski’s engine in shallow water where it can suck up sand and weed, potentially clogging the intercooler or even reducing its efficiency.

You can tell if an intercooler is struggling because the jet ski will slowly, rather than suddenly, lose power.

The key to keeping a supercharged jet ski in peak condition is to service it regularly.

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