[NoDOHC]

The rule of thumb I go by is that you want 0.3 mach in the intake runners at peak torque and uniform cross-sectional area from the plenum to the port. Slight decreasing in area is acceptable as the air enters the rotor. The plenum should be 1.5X the displacment of simultaneously charging volumes (in your case .654 l).

You want to tune your manifold for 2nd harmonic at peak torque to allow for reasonable additional tuning possibilities (3rd and 4th harmonic will also assist you).

Rotary intake tuning is signicifcantly different from piston intake tuning because the chamber charges twice as often (once per revolution).

Basically, the stock manifold follows all the rules except for the mach 0.3 rule. at 100% VE we get 0.18 mach (average) or 0.33 mach during the 198 degree intake stroke at 7,000 rpm (too small).

The secondary plenum is about right for the turbo engine, the primary basically doesn't exist.

These rules are what I have compiled from reading a lot of manifold design papers and books, most of the information is for piston engines, but I think most of it can be transferred to rotaries.