I know another member on this forum is developing an intake manifold for the Z33, but here is one from a Japanese tuner.
Not much information. Just saids that simply bolting this on will increase a suprising amount of HP.
Click

 

what a tease! id like to hear some more about this!
franklinz

 

Seriously, when is the intake manifold coming out?

 

There's really not much info on it.
Here's the link to their Z33 section.

 

That has been posted before. All it is is the spacer, to raise the plenum up a bit. This isn't a full plenum. Doug's increases air flow primarily to the front cylinders, which are starved for air much more than the back.

Not sure if this will be as effective as Doug's.