The gain on this would be very little and hardly noticeable. You would notice more sustained power more than any power GAIN. To do that, boost must be increased, being fuel injected-the engine needs to be tuned for ANY upgrade done to this. The principle is simple. Just as any car/truck. Most everyone wants more power so the cheapest, easiest way to buy a Cold Air Intake kit. Well, this sounds good in theory but the vehicles now adays have a mass air meter or other metering device measuring the intake air volume/temp. If the computer sees more intake volume due to the new CAI that was installed, it will simply "de-tune" the fuel in conjunction to essentially not make any more power. Once you TUNE the computer to read more air and not follow predetermined parameters, it will add more fuel for the added air and THEN make more power. The same applies to these boats. All the upgrades need to be tuned to gain their full potential-ribbon delete, intercooler installs, re-pitch on the impellers, etc.
Once we have a hand held tuner available for these boats, thats when we will see them come alive. ESPECIALLY with them being supercharged. I honestly dont know why they didnt go turbo. Turbo is free power and supercharged isnt. You are constantly using power to make power on a supercharged engine. If I had the money or time, I would love to fab up a turbo on one of these engines and mess with the air/fuel to really see what these little engines are capable of. They say they are rated at 220ish HP now, I see 275 being easily achievable with a turbo, larger injectors, and a nasty tune (All be it negatively affecting the gas mileage which is already terrible). Getting it "too the ground" or water in this case would be the hard part. Playing with the impeller pitch and other variables.