The Stage V head actually has an intake runner that is too big for a stock 426. Sure, they will run, and will make reasonable power in the upper RPM, provided you want to spin it hard. But...at low engine speeds, the port velocity is pretty slow on an engine that small. Torque will suffer, as well as efficiency.
Velocity is paramount to cylinder filling. A slow moving intake charge will cease to fill the cylinder very soon after the pressure differential is equalized. Cylinder filling after bottom dead center is an important factor regarding efficiency & horsepower and is just as important as the initial charge and how well it is drawn in.
The exhaust port is excellent though, especially with a 1.9" valve.
I am using a set on a 605" build right now. The intake port was actually large enough, as-cast, to support 6700 RPM on that size of an engine.
We sell complete Stage V head packages, but I feel a moderately ported OE head may be more suitable for your application. I have not seen any problems with the Mopar performance aluminum head provided that they get heat cycled and the seats are cut perfectly with no runout. I cover these procedures on the build I am doing now on my FB page.
As far as quality, fit, finish and consistency, the Stage V heads are works of art. They will be the base head choice on our 528+ engines.
