Recently installed Whipple Charger on my formula 271, ran awesome for 25 min, slowed up, motor started running like a plug went out, then like it was coming apart. Idled to ramp checked plugs #3,7 full of water. 2468 all moist not soaked. Drained/ unhooked manifolds, cranked over motor with plugs out same amount of water, comes out of spark plug hole. Assuming it's blown head gasket from added pressure. No water in oil, and plugs were new, never wet until test drive. one way or another it's coming apart.
How big cc. heads could i use with blower 6/7 psi, and be efficiant.
Any tuning with computer (ie reflashing), like to keep as simple as possible. This is the older style Whipple, mounts off the side of intake.
Any thoughts would help, Thinking AFR aluminum heads, boat has closed cooling

You kinda got a head of yourself on this conversion project.
You've got tto remember that a marine motor with a supercharger when operating properly is a real sophisticated total engine system. You can't just take an existing motor, clamp on a supercharger that wasn't even designed for marine use and then wonder what happened with not system approach to setup compnent matching and proper tuning.
My suggestion and recommendation is to stop while your still ahead, back up and decide if you want a supercharged marine engine in your boat and its real performance benefits versus costs. Then if you're set on supercharging, either take your motor to a quality marine engine builder with proven supercharger success or start your project yourself carefully from the ground up with real good factual information and quality recommendations on how you can put a complete supercharged engine package together for your boat that will have all the right parts, systems, programming and tuning that will develop the reliable power you most likely need and are looking for.
If you continue piece mealing the thing together with more parts and money you will frustrate the hell out of yourself, limit you boating pleasure and put serious dents in your wallet!
Just my two cents here again, but read between the lines!
Don't be penny wise and pound foolish!

Best Regards,
Ray @ Raylar

If the boat has closed cooling, the only place water can get into the cylinder from is the exhaust.