The crankshaft rotational point and the amplitude of maximum vacuum from piston motion varies with:
1. connecting rod to stroke ratio
2. compression ratio
3, buffer volume upstream of the intake valve including intake port, manifold runner, plenum, etc.
4. buffer volume of exhaust gas remaining in the chamber from overlap
5. overlap triangle area (Vizard: the area is roughly proportionate to the square of the nominal duration)

Are these factors quantified, and blended into the prediction as contributors to spikes?