You didn't consider that? It's the first thing I though without the pics. Here's what happened--the rings butted from excessive heat ie. pre-ignition not detontation < those are two diff things. The ring gaps weren't set large enough and OP had a tune that was not in the safe zone. End of story. Blew the top off the piston and smashed the electrode. It didn't happen on DW or you would have noticed the miss then. It happened very recently most likely. Get a boost referenced timing/fuel system and dial it in , in small careful steps. J.Rob
