What broke in the Charger's engine at the end of the movie?

It was a thrown rod in one of the cylinders. The focus on the oil gauge would lead us to believe his oil pressure dropped too low once he revved out in his highest gear. It was probably blown toward the head rather than the block since it's less likely that the car would continue to be drivable if the block was damaged by it. In all reality it's more likely it wouldn't have been drivable either way after that. But that is supposedly what happened. I suppose the rod could've broke off at the cap or from the wrist pin on the piston but either way is going to result in a seriously messed up block. Otherwise the rod cracked from low oil pressure or the increased pressure from the NOS or maybe even both. I think he used nitrous in the Charger right? Been a while since I've seen it now.

Looked like a spark plug blew