V8 engine exhaust collector

This is an old model which failed to render in BlenderInternal. But now as I test in a newer version, it renders. I gave this a try after my model yesterday stopped rendering in BlenderInternal. I fail to find an error log or message. I think I already added an animation where a collector rotates around the exhausts and collects the pulse to feed them into a turbine. May have been only a plan in my head. I have done preliminary tests to change the modeling of the top cylinder surface. Blender boolean does not care if meshes have holes, as long as the other mesh does not touch them. Using this I had planned to model the region around the valves as a body of rotation, add some triangles to give it an onion shape and somehow use array mirror to do an almost mirror to prevent edge cases for boolean union, triangulate, decimate.collapse, decimate.flatness. Then subtract this from a flat plane.