What really splits blocks is the lack of material in crucial areas. The cracks typically start at the main journals and work their way up through the lifter valley. Detonation is not the cause of the block weakness. That's not to say that it wont contribute to failure...it's not the cause. What really splits the block is the exceding of the torque limits put on the mains and webbing. I've said it before, stock internals will outlast the stock block...be them forged or hyperutectic. As far as n/a outlasting f/i goes...I don't see it happeing at similar h/p levels. To reach the h/p levels you get with forced induction requires extremely high compression and extreme rpms. Your streesing the living hell out of the block doing so...and it's not going to be any more safe than a f/i or nitrious setup.