Some thoughts………
Happy Holidays!
Re-programming the engine to a 425 alone will not get you a faster boat. You still have the same gear and propeller pitch. Propellers move boats, engines just turn them. There is a great article in the Tony’ Tips section that explains this.
https://www.sbmar.com/featured-article/propellers-move-boats-engines-just-turn-them/
Look at what Tiara does to the gear ratio and the prop pitch on the boats from the factory outfitted with the 380 vs the 425. I attached the Tiara performance reports and it shows that they come from the factory with different gear ratios and prop pitch.
The 380 has a 2.04 ratio and 23×30 prop
The 425 has a 1.96 ratio and 23×31 prop
That is how Tiara makes the 425 equipped boat go faster. Since the 425 has 1 to 2 GPH more fuel burn at 2400+ rpm there is more power to turn the gear and prop. Thus the higher speed.
Compare them at 2400 and 2600rpm. See the higher fuel burn on the 425 that is then transmitted through the bigger gear and prop. That is what gets the boat moving fast. Not just the added HP, its the HP+Gear+Prop.
The easy way to get your boat to go faster in its “As Is” setup is to carry less weight. Like fuel load. You can pick up 1 to 2 mph by carrying a lighter load of fuel. We have a different boat but we have the same fuel capacity. 400gallons. I notice that when we run “light” 150gal or less we move along at about 1.5mph faster with a 1 to 2 GPH lower fuel burn.