How did you get all the plastic dust and shavings out of the manifold? Air compressor? Shop vac?

I'm doing something similar and I noticed there are a lot of places where the little particles can hide and get sucked into the engine later. As you know, the the entire inside of the manifold is open and has little nooks and crannies everywhere.

water pressure has done a very good job cleaning everything
you can also minimize the dust/particles going in by putting some towel in each runner

Ah! I didn't think about water.

These manifolds are quite sloppy in their construction. Lips left over from the molding and sharp edges in the runners shouldn't be there.

Megan, thanks for all the good info in these threads.

How plausible do you think it would be to split the stock VHR manifold open for modification?

I'm very interested in modifying the internal geometry of the manifold, if I could just get it open to work on it. It looks like one solid piece of cast plastic, I don't understand how they could manufacture it that way... haha.

Thanks!

They may have molded a top/bottom half and sonic welded it together, or maybe even glued it together.

Probably sonic welded. It looks completely solid to me, not glued.