the valve springs & cylinder heads even the properly sized/tuned induction & ignitions systems
are usually the biggest limiting factor to higher RPM's,
lack of oil, weak or poor valve-train components, weak push rods,
the lack of good rods or a min. good rod bolts, even some bolts/hardware,
head & crankshaft retention, block design/strength, weak mains or webbing,
pressed wrist pins in cast pistons, instead of full floating with forged pistons,
any decent pistons & rings {not cast, skirts break easily}, internal balancing
all can be contributing factors, not only limited to,
the use in higher RPM & staving off catastrophic failures
BUT the cylinder heads are a really big choke point,
"usually" especially on Mopars
generally the better heads/induction/valve-train work in together &
properly matched, then a way to exhaust it more effectively/efficiently,
then maybe the higher the RPM's...
The bottom end is a different story, oil is the life blood,
an abundant supply 1 qt for every 1000 RPM, at ample pressure,
the short block/bottom end, it's basically just an air pump,
hopefully with good compression, oil retention/supply & ring seal, balancing etc.
It's the heads ability to flow, camshaft/valve-train & induction/fuel system & ignition,
dictates allot of outcome, {even the weight of the valve-train pieces}
make a difference in the ability to keep pulling, in any performance applications
bottom end needs good quality machining, balancing & "usually" forged parts, to help it live..
