Rotax 1630 ACE 350: How the Sea-Doo Engine Works, Fuel, Diagnostics and Tuning

The RXP-X 350, RXT-X 350, GTX Limited 350 and RXP-X Senna 350 all run the same engine: the Rotax 1630 ACE 350. If you wrench on your own ski or tune it through software, you should know what's working in there, which systems talk to each other and where to look when something's off. That's what this page is about, from the shop's point of view rather than the brochure's.

The key numbers

BRP calls it the most powerful production PWC engine in the industry. Through 2026, the same spot was taken by the Rotax 1630 ACE 325 with 325 hp. Which models changed and what else is different is covered in 2027 Sea-Doo 350: what's new.

Supercharger and intercooler

The supercharger compresses the intake air before it reaches the combustion chambers. Compressed air gets hot, and hot air carries less oxygen for the same volume. That's why the 350 has an external intercooler in the intake tract to cool the charge back down after the supercharger. For you as a rider, intake temperature and intake pressure are the two values that tell you whether boost is doing what it should. If the throttle feels soft after a long day in warm water, that's the first place to look.

Closed-loop cooling

CLCS stands for Closed Loop Cooling System. The engine is cooled by its own coolant circuit instead of having the water you're riding on flushed straight through it. That keeps salt and sand out of the engine internals. Engine temperature is still one of the values worth keeping an eye on, especially after a software change.

Fuel: premium, but which one

BRP calls for premium fuel and lists 91 octane for the US. That's the number you see on the pump in the States, so for North American riders it's simple: fill up with 91 octane premium as your owner's manual says. If you ride abroad, don't try to convert it yourself, because other countries use a different rating method. Once you tune, the M-JET FLASHER setups are split by fuel type anyway, more on that below.

iTC and iBR: the electronics behind throttle and brake

Throttle response on the 350 runs through iTC with several modes. In diagnostics, throttle lever and throttle body show up as separate values, which helps when you're troubleshooting: if the two don't line up, the problem is more likely sensors or calibration than the engine itself. Brake, neutral and reverse are handled by the electronic iBR, which has its own control unit and its own fault memory. So if the ski won't settle into neutral cleanly, don't just scan the engine ECU, scan the iBR too.

What to check when troubleshooting

With M-JET DIAGNOSTIC you read up to 180 live values, depending on the control unit, in an app on your phone. No laptop. On the 1630 ACE 350, these are the most telling:

• Engine rpm and engine temperature
• Intake temperature and intake pressure
• Throttle body and throttle lever
• O2 sensor and fuel pressure
• Ignition timing and battery voltage

You also get component tests: ignition coils and injectors can be fired one cylinder at a time, and the fuel pump in three stages. On a triple that runs rough, that narrows down a problem cylinder in a few minutes. After throttle body work there's the TPS reset, after maintenance the service reset. You can log test runs and compare them later.

The power lives in the software

The engine is run by the Bosch MG1CA920. That's where the maps live that ignition and injection follow. And that's exactly where the M-JET FLASHER comes in: the dongle goes on the diagnostic port, the app on iOS or Android connects over Bluetooth, you pick a setup and flash. After a few minutes it's done and the flasher comes back off. The app shows which setups are available for your 350. There are OTS maps for different fuels, and the stock file can be restored at any time.

There's one requirement: the ECU has to be unlocked once before the first flash. How that works through Germany, Florida or an already unlocked replacement ECU is explained in Sea-Doo 350 ECU unlock. The fact that 2027 ECUs come with new software versions isn't a problem. The flasher reads the version, and if it isn't on the server yet, the tune is built in max. 3 business days.

Same foundation as the 325

If you know the previous generation, the ECU holds no surprises. Both generations use the Bosch MG1CA920 and sit in the same model group in the flasher. What else differs between the two engine generations and the skis around them is laid out in Sea-Doo 325 vs 350.