Sound proofing my out board engine.?

Glue flat stuff in and fill the gaps with great stuff. Don't plug any vent holes. Form the great stuff while it's expanding with a putty knife sprayed with silicon.

The inner of the cowl gets very hot... expanding foam of any kind is flamable,,,, go to johnson outboard dealer and buy the treated foam from there.... to be honest the noise reduction you will get it minimal... if even noticeable becasue of the way in which boat motors are built... one inch of foam will basically do nothing.....

Most of the old motors didnt have foam in the cowls ...

I though the foam was there to protec the motor when you lift the cowl off..

The spray foam wont take the heat , get the correct rubber foam as it last longer an is fuel resident.

talk to your local upholstery shop or high end car audio store either of them have what you need and would either fix it for you for a fee or sell you the stuff to do it yourself. If you want them to do and save a little money prep the area by removing all the old heat/sound barrier and remove the cowl from the boat

do not use great stuff on your engine......if it happens to catch fire it puts off a toxic fume that can cause serious damage to you or your passengers. Just glue in some flat foam that you can get at almost any marine shop for sound proofing.

don't do the foam. very dangerous stuff in that environment. check the local hardware store for some thin insulation that is fire-retardant. there are several types.