I hope you are well.
I have a Phantom 25 from 1984. Its made a little heavier than a standard P25 according to Steve Baker. in 2016 i reinforced the foredeck with Divinycell, so its even more heavy now. But stiffer and better in high seas.
I have owned several engine configurations during the 20 years I have owned it; Johnson 300 V8 GT3,6 Offshore, Promax 300 SVS, 2 x Merc 2.5 EFI SS PCU, Verado 350 Sci and now a Verado 400R. Its been a very fun journey
The boat ran 75-76 mph with the Johnson and Promax engines. 86-87 on a best day with the twin 2.5 EFI SS engines and 80-81 mph with the single Verado 350 Sci.
Last year when I bought my 400R we managed 85-86 mph with a REV4 25 pitch propeller at 7,040 rpms. The gear ratio is 1:1,75. Propshaft 0,5 inches above the bottom.
I bought a new propeller this Spring. Its not cheap but it proved to be a success. Its Max5 five blade 25 pitch propeller. This propeller was made for the new Sportmaster lower unit mounted to the 400R. Its a high rake 15 inch propeller.
We managed 86,3 mph out of the box with the propshaft even with the bottom. Next run we managed 86,7 mph with the propshaft 1 inch above. Next time 87,7 mph with the propshaft 1,75 inches above the bottom. Two weeks ago we did a new test run and did several 88,6-88,8 runs with the propshaft 2 inches above the bottom. We managed in the end 89 mph at 7,060 rpms with the propshaft 2 inches above. So the trick is to get the engine as far up you can go before loosing waterpressure and bite.
We are now hitting the soft limiter at 7,060 rpms, so I will add 0,5 inches pitch. This will bring the rpms down to 7,000 rpms where the engine makes most horsepower. And we will most likely cross the 90 mph speed
Great fun with a classic that runs so good in high seas and smoke most of the new hulls around with equal horsepower.