I've been trying to explain this to guys for years. The IVC alone doesn't acount for volumetric efficiency. The port CSA and approach angle, the intake ram tuning effect, rpm, and several other factors play a role. A 10:1 383 with stock 906s and a long runner dual plane will detonate before the same spec engine with -1s and a large single plane. Higher port velocity is more efficient at filling the cylinder at lower rpm where detonation occurs. That inertia is going to be different among different engine combinations, regardless whether the dynamic number remains the same.