Heard some nasty knocking at the end of the last trip. I shut it down immediately and floated to shore and load it up. Fired it up and no knocking at idle. Tore down the motor yesterday to find this. 

there goes the neighborhood ouch...are you done for the season?

Its not an Olds, its a BBC 454. Hopefully not done for the season. I calculated the cost of a rebuild to be about $1750 but that included some performance upgrades too. Doing all the work myself. The good news is I have 2 other buddies that co-own the boat with me, so that price will be divided up by 3. The bad news is I currently do not have one of those income producing opportunities, also referred to as a job. I will keep you guys posted with pics as I make some progress.

Its not an Olds, its a BBC 454.

You have to forgive Tony, he dont know what a "REAL" engine is
Good luck with it.................

2sav

jus slap some pistons in it and lets go. watch your timing and gas

That's what my buddy said too. I think it was from running it last year on a carb that needed a rebuild. It would drip gas out of one of the bowls. So when the boat was WOT it would ping a little. This year, I rebuilt the carb and added OT headers, and the boat ran great no pinging. I am deciding between hypereutetic or forged pistons. Some say the cast ones won't last on a higher RPM motor. I turn about 5K RPMs now, but would expect to turn 5600-5700 next season. I was hoping to get a 850 DP carb and Clay Smith cam with roller rockers and heavy duty springs. Not sure if that will happen this time or it might have to wait until winter.

Sometime ago, I was engaged in a discussion with a long-time Speed-Pro employee who was in charge of manufacturing.  He stated that when subjected to enough detonation, the BBC pistons in particular are notorious for melting through the piston crown to the top ring, in exactly the same location where yours broke through.  This is because the ring land gets very thin at the perimeter of the piston where that valve relief is, and so that area of the piston crown gets hottest the quickest and before you know it you can see the topside of the compression ring.

And this is how you prevent it from happening again. 

LO

Just to add to this, a cylinder head to piston distance with a pinging engine can add to this phenominon, it is the lack of adequate "quench" area between the piston dome and the heads "flat" surface, it will create an incredible "hot spot" pretty much right there at about 2 O-clock, seen it a dozen times before, especially on engines with a lot of deck to head clearance, like when using thick head gaskets to try and lower the CR.

Another issue is carbon build up on the rings, sometimes enough carbon builds between the rings and the lands and expands to pop the land apart, I believe you mentioned a carb flooding/pinging issue, probably did not help.

Just my opinion, but go forged, your not going to save enough $ to build it twice, and forged are proven as a good buy. Speaking of good buy, check out the Summit website, Keith Black makes a budget minded set of "real" forgies for a descent price. Worth every penny IMO. Those look to be .040" overs, make sure your machinist looks/measures before ordering anything (you may get by with one piston, all rings and a hone job)

My "new" motto, "Do it once, do it right".