I was wondering how people normally do a complex core design.

Task: a Y-Branched 90degree reducer path for a flow meter.

My situation is this:

I saw a photo on goggle and the design is exactly what I’m looking for.(but my one is like 1000times smaller).

I've done my design  of the outer pattern of the casting, and having trouble to drawn up the core.

The aim is to design is core is Y-Branched 90degree reducer path and run with flow simulation and work out the best geometry to minimise the turbulence.

So far I've achieved is to us Ellipse sketch and sweep feature to make the top half, loft feature to produce the bottom half, then fillet feature the joint and use the flex feature to bend 90 degree.

Nut couldn't get the mold parting done properly

Also I'm sure there is a better way to drawn up the geometry as shown on the attached photo.

Please advise of there is any tips for complex core design, and how would you draw up this geometry.

I hope I am explaining this clear enough.

Update10/07/12:

I've tried to have manual parting surface this morning  and still stucked wih tool split feature.

Part file has been added ot the attachement.