[dataway]

I started out doing the intake using "Lofts". I create an outline of the intake port at the flange, create another outline of the hole where it would enter the plenum and the program generates a "shape" that connects the two, then I add a "rail" which is the path the shape would take ... like a turn into the plenum.

I found that approach problematic and way too complex. So I started from a top view of the intake and drew an outline of what each runner looks like from the top surface, then extruded that downward the right depth. That gives me an approximate solid shape. I then carve that shape further by creating solids that I then "subtract" from the first solid. The outlines use a combination of arcs, and spline fits and individual radiuses to achieve the basic profile of a runner.
After the shape is real close to what I want I use Fillet and Chamfer commands to round the 3d edges (like the runner corners) or places like where the runners join the flange to simulate the casting process better.
Since I'm using CAD tools for this I have very limited ability for automatic smoothing. If I was using software like 3ds Max, a modeling and animation program, there would be many options for automatic smoothing.
The method I am using is very much ... what you see is what you get. Lots of compromises between what looks the best, and what will actually print. I'm starting to learn that something just need to be printed in two pieces to get the proper detail. Like the distributor ... no way I can print both the cap, and the shaft as one piece and have them turn out correctly.

I might revisit the cylinder heads and print them each in two seperate pieces to get the details I want on both the front of the head, and the exhaust side of the head. This is a problem that injection molding doesn't have in most cases, it can print in equal detail on any side.

The intake needs some work yet, should finish it off tonight and try a print. And I'm finding I need more clearance between the air cleaner base and the radiator hose in front, and dist. cap in back .... so I need to go down to the shop with a tape measure and look for any gross errors I might have made.