I had one look like that and it lost the Valve seats

assuming you are running a retuned merc ECM ? injectors seem small..don't think that caused the issue...look at block passages closely...seen some clogged and over heated certain cylinders...would be nice to have a tunable computer and be able to "see" certain data on a laptop...I am running a procharged 500HP with our own EFI system using a megasquirt computer...but running 96lb injectors...if you go to a injector sizing table you will see those way small...I am not done with the EFI change over yet...just got back working on it last week...hope to be running in a couple of weeks...

The boat has a Aeromotive A-1000 And a 2:1 FMU on it. I guess i never really seen it until you guys pointed it out. but if for sure does look like the HG may be the issue! Very good catch. There were the Felpro gaskets. Guess i should switch to cometic? or deck both surface and reuse felpro?

Detonation probably took out the gasket, mill the surfaces and use MLS gaskets, but first, find out what caused the detonation so it doesn't happen again on the next power run. You may want to install a wideband 02 to keep an eye on A/F ratios as you're running.

I'll only add this for reference, but I use a 42 lb injector on a N/A 377 cid small block.

I have widebands, refer to first post. AFR was low 11s at wot.

detonation can have many causes, could been bad gas, maybe too small of injector, maybe fuel delivery issue, with a blower anything can happen easier....

BBC don't lift heads that easy and 6-7 lbs isn't much.... The gasket sealed fine that's not a head gasket fail, you were sealed just fine to burn a piston, I would verify fuel delivery and get EGT on it so you can monitor WOT EGT's

again, that's NOT head gaslet failure.... its simple detonation

Once back together we are going to check the injector drivers in ecu! Will keep everyone updated! Would a 10-12 PSI pulley really jump up power? And I have a whole new fuel system for the boat. Twin Bosch 044 pumps. and 1000CC injectors.

Might want to check the gph on those pumps at 55psi. Might want to think about race gas at 12psi.

Fuel Pump Comparison Test : Real Street Performance Engine Parts, Pistons Rods Cams Valvetrain and More