Enya .09 Tongue Muffler Question

[Chancey Chorney]

Hi there. So I had made a tin tongue muffler for an old reverse sided exhaust Enya .09. Anyways, the main question is how many holes does one put on a tongue muffler, and size as well? As this is going to be on a platter type plane, is there anything wrong with drilling my holes on the topside facing away from the plane? Thank you.