I don't see any etching around the edges of the piston in the pic above, that's what detonation does. Doesn't look like detonation to me, looks like something bouncing around in the cylinder.

All I know that gas is garbage and 1000hp blower motors aren`t going to have a great flame front at peak tq with crappy gas. If it wasn`t preignition with that gas why am I putting 93 octane with boostane in my tanks, might as well run 87 octane if it`s all good. and that it happened 10 minutes after I filled up, that`s just a coincidence?
The seats were pounded into the heads on both motors, pre ignition/extremely high cylinder pressure .
Intake valve broke in half from the cylinder pressure and had a party in 3 holes.

If my head guy who I have dealt with since H.S. who said bad gas before I even said anything .....it`s bad gas, don`t care what the internet says .Sorry.

I had a Titanium Del West exhaust valve stick in the guide once. Broke in two. Motors had a CR of 9:1. Del West didn't want the valves in a CR application less than 11:1. Del West said higher CR normally runs with a cooler combustion chamber. Who would have thunk?

Corn is for FOOD.!! As far as I know you cant turn oil into a potato. Massive reserves of Oil, clean burn technology...Simple

I run E-85 in a 900hp turbo engine, in a car. I do that because the E-85 has a much higher octane, preventing detonation at higher boost levels. It does require about 40% more fuel than gasoline would require. Alcohol generally runs much cooler. Not sure exactly how that valve broke, and bounced around in the cylinder, but pretty sure it's not due to detonation or a lean condition causing a piston to burn through. The only time I have ever seen a valve break like that is contact with a piston. I would say it's best to stay away from ethanol fuels in boats because of it's ability to collect moisture from the air. Ocean/Lakes are very humid areas.

What octane are you mixing the Boostane to? My new boat needs more than the 92 I have available in my area just curious your experience with the Boostane if it's safe to run reliably.

BTW, sorry to see that TOTALLY sucks ass!

I’ll flip the direction of thoughts on ethanol- Ethanol fuel is most likely responsible for the demise of rubber lining of fuel lines that swelled shut. Did you replace with ethanol friendly fuel lines.

Good point. When I bought my boat I replaced all the fuel lines with ethanol compatible because I knew that’s all the fuel I could get.

I'd be finding a new head guy. There's not one single piece of evidence in the piston top to suggest a fuel issue. It'll damage the piston long before it hurts a valve that is tight against it's seat. Valves break from being stuck in the guide and smacking the piston or because of inadequate spring pressure allowing the valve to bounce and eventually snap the stem. Sorry you not willing to accept the truth. Even if it is from the internet. With multiple experienced people telling you so.