improve air flow. The surface roughness I was also speaking of was not mirror polishing as I noted with the 300 grit sandpaper analogy. I understand your point on the boundary layer with the Z plenum design and downstream location of tyhe injectors. However the air accumulated in the upstream portion of the plenum does have fuel mixture in it because I believe the injectors are not timed to valve opening in the Z32 but pulse at a selected rate based on air flow cfm measured at the AFM (and other measurements). Therefore there is accumulated fuel vapor in the plenum but no doubt less than in a carburated manifold desugn. Thus there is a fuel boundary layer accumulated in the upstream portion of the plenum and finish of the manifold would appear to have some effect. Have you ever flow tested a plenum design like the Z32? I would be interested in the B4 and after results.
