* Internal Components: The crankshaft, connecting rods, pistons, and other internal parts determine the engine's strength and ability to withstand high horsepower. Stock internals are good for relatively low horsepower (maybe 350-400hp reliably, potentially more with careful tuning and driving), while forged internals (crankshaft, rods, pistons) can withstand significantly higher horsepower, well into the 600-800hp range (or even more with specialized components and expert building).
* Cylinder Head Flow: The cylinder heads' ability to move air and fuel into the combustion chamber directly impacts horsepower. Stock heads are restrictive, while aftermarket performance heads significantly increase airflow and horsepower potential.
* Valvetrain: High-performance valvetrain components (camshaft, springs, retainers, etc.) are essential for handling the increased stress from higher RPMs and higher horsepower.
* Engine Management: Proper tuning of the engine's fuel and ignition systems is critical for reliability and power at any horsepower level.
In short: A well-built 377 with forged internals, performance heads, and a proper valvetrain and fuel system could easily handle 600-800 horsepower or more. However, a 377 with stock internals might struggle to reliably produce more than 350-400 horsepower. The horsepower figure is entirely dependent on the build.
