Plans suggest you put a rubber seal around the cowling inlet and the FAB snorkel housing. You must allow some space between so the engine movement doesn't jam the FAB housing into the fiberglass cowling, maybe 1/2 to 3/4" space.
1st challenge is creating a seal for the in rushing air to not leak in under the engine defeating cooling airflow.
2nd challenge is to make the seal easy so as not hinder lower cowl installation & removal - especially for an 'A' model.
Fiberglass work involves shaping the cowl inlet to a similar shape as the FAB front opening. There are many different ways to attach the seal material to either the FAB or Cowl, or both as I have done on some 'A' models I did (top seal half attached to the FAB, bottom overlapping seal half on the cowl, not perfect but worked for the most part, especially on 'A' models).
The best air inlet/seal I did was with a removable front inlet. I used mould release in the area pictured in the above post, laid up a few layers of fiberglass inside (popped it out after curing)to create a flange, than cut the inlet off the lower cowl (removable, to be held on with 3 screws), the fiberglass inlay was than trimmed to form a flange, glued into the lower cowl, & drilled for nutplates to create the removable cowl inlet flange. Than the inlet rear edge was shaped with fiberglass for mounting the rubber seal to conform with the FAB housing. This mod made lower cowling installation after maintenance MUCH easier, as well creating the best inlet seal I've accomplished ever.
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Ralph
Now retired - my builder assist shop now closed, 
Last edited by Ralph Inkster : 08-24-2023 at 04:02 PM.
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