Water Dissolvable Mold Core Material
Pre(r)amble - Probably get some snide remarks for this one, but it worked. Hurricane is on the way and the office is a ghost town so here goes.
Background - Very specific to some Rocket air box/inlets but I assume most readers don't go there. The inlet to airbox path is not aerodynamically smooth if left un-modified. Order of assembly makes fairing this in a bit difficult. Likewise, The geometry doesn't allow foam use without some type of adhesion, something I wanted to avoid and preferred not leaving the foam installed which would require venting of eth enclosed area(s). I posted here regarding foam product suggestions but got more warnings than anything; always appreciated.
Searched for water dissolvable mold core products. Found nothing practical. I experimented with cheap-a$$, readily available, zero harm drywall joint compound (mud). Was able to "hydroblast" it out of a one inch pipe using an engine cleaner/sipon gun. I applied it to the fair in the scoop flow-path. Not completed done but 45 minutes of compressor time has got it 75% removed. Gonna soak the insides before the next blast. The internal mold passages are very thin.
(-) = It shrinks. It cracks. Thick fills take a long time to dry
(+) = Super cheap. Available anywhere. Sands easily. Smooths easily with water, sponge, wet finger, etc. Environmentally nil; and most importantly for this application, Water Dissolvable.
Thanks to Toobuilder and later WireJock for the packing tape/mold release suggestion. Works like a charm.
Not saying this is the best technique or possibly couldn't have been done another way. It could be a very useful arrow in your fabrication quiver. As others here state, YMMV.
Some pix attached = unfinished/aerodynamically challenged, roughed in, and core removal.
Fiberglass. One more thing I don't like and suck at!