Ive got a completely fresh 350 long block back from the shop, its got brand new aluminum heads (2.02 , 1.60), lunati split duration cam with 1.6 rockers totaling around .530 lift, steel crank, all being backed by a 700r4 but here is the unsettling part... cast pistons. i sent this engine to the machine shop a long time ago and hadn't known as much about parts matching as i do now, that machine shop was lazy and i have found a much better place i take all my engine to now. so the question is what are my limitations in terms of rpm? should i get these replaced with forged?
RPMs are more a limitation on rod reliability and ring seal than the piston. The piston itself is more at risk to detonation and preignition for sudden death. At that these events usually cause a ring failure that takes out the side of the piston. That is because detonation and preignition raise the temperature of the rings beyond the ability of the gap to keep the ends apart. They butt together to bend the ring till it busts the piston. Old mid alloy cast pistons usually hold together but burn out a side or loose the center, hyperutectic castings will take a much higher beating than old alloys but when they go they frequently just come apart and let he rod and pin bash the bore wall to death. Forged pistons push the failure limit higher and usually hold onto the pin and rod when they fail but they certainly aren't immune to failure.
Often at high RPM it is the inability of the rings to maintain seal that leads to detonation and preignition failures by allowing large amounts of oil into the combustion chamber which quickly reduces the octane rating of the fuel resulting in detonation. Or by forming carbon deposits that overheat causing preignition. In actuality both of these things are happening at the same time in this operating condition.
As for your pistons it depends a lot on how often the engine goes to high RPMS at and over 6000 and how long it stays there. In actuality if the rings are gapped in the expectation that the engine will run fast and hard for long periods or be subjected to heavy shots of nitrous or super charging of some sort it is possible for cast pistons especially hypers to put up with the power forces rather well.
So it comes down in many ways as to how the engine will get used. And of course what you haven't mentioned which is what are the rods, what is the crank, is the block a 2 or 4 bolt, how well is the rotating assembly balanced, and how good of a damper have you put on it.
Bogie
