Converting a 320 cowl for a 360, How I did it, this is a cut & splice saga... sorry no pics...
I found I had to increase the cowl depth by 1", & widen it to accommodate the larger FAB360 air box. Along the way I drilled temporary holes in the lower cowl for screws or clecos as needed, easily filled in later.
- cut a plywood panel to the shape of the lower firewall - so it fits inside the lower cowl & preserves the side to side & vertical dimensions of the existing lower cowl.
- use a dremel tool to grind the inside fiberglass layer and honeycomb back where needed. Caution, don't grind into or disturb the outside layer. You can than use a micro slurry to re-seal the honey comb edge and create a sloped transition from inside & outside fiberglass surfaces. Follow up with a couple layers of glass over that and strengthen the outside layer.
- screw your plywood form to the lower cowl to stabilize it.
- use an oscillating cutting tool or similar to cut the side wall of the scoop/exit port off the bottom of the cowl.
- use a series of aluminum strips to space the scoop away from the lower cowl (in my case, 1") & attach with a couple clecos per strip.
- once you have the required vertical height you want, tape some light poly plastic sheeting to the inside of the cowl, forming a pocket along the gap you created.
- prop up the cowl on it's side.
- mix up some 2 part urethane foam and pore it along the gap, just enough so it expands thru the gap & you can sand it down to the required shape. Repeat foaming & shaping on the other side.
- lay up 2 layers of glass over the gap joining the scoop back to the lower cowl. All around.
- next day, remove the plastic, chip out the urethane foam, & remove the aluminum strips & clecos.
- lay 2 additional glass layers to the inside surface of the cowling for more strength.
- you've basically done the scoop depth modification, now to widen the scoop for the FAB360 housing.
- cut the whole scoop off the lower cowl, about 1" outboard of the scoop all the way around.
- split the scoop in half front to back.
- using more aluminum strips, cleco the two halves back together to the required width using more aluminum strips.
- again tape a plastic pouch inside of scoop, again follow the foam, sanding, glassing as above to join the two halves of the scoop.
- use scoop to trace new cut out on lower cowl.
- repeat again the clecoing, glassing steps to make the cowling one piece again.
Sounds like a drawn out process but realistically can be done in 2 days with cure times. Smoothing out and getting ready for paint afterwords is just another joy working with fiberglass...
If you are just mounting a new scoop to the lower cowling, I vote for mounting it to the outside (this prevents internal flange areas that might later infringe on exhaust/alternator/or other interferences), glue it in place with a epoxy/flox mixture, after it is cured, grind the square edge off from around the scoop & feather it smooth with micro/epoxy slurry layers.
Inside the cowl, seal any exposed honeycomb with a micro slurry, followed up with a couple layers of light glass.
or
You can follow some steps of the cut & splice process above for flush.