I've had PMs asking about drilling the stock muffler, so here it is again,
Simply 8 1/4" holes evenly spaced,.... drilled on a 1 5/8 dia circle.
Be careful when drilling thru, as some have reported breaking bits
while striking material on the backside.
The holes in mine are 5/16 now,......can't say it is much louder than 1/4" holes.