You don't need any more or larger holes in the muffler outlet.
I gutted the mufflers of two of mine, one I took out the cat and the plate the cat
is welded onto, this had the effect of needing a little too much fuel to keep the saw
from running too high in the revs, so that saw needs to be let sit until it is as hot as
a sitting saw gets, so when cutting it reaches a temperature high enough to burn clean.
i use it for cutting logs into rings in the yard, that way its flat out most of the time and does
a good job.
Its identical twin, I just cut the spot welds holding the cat off and left the plate the cat was
welded too in place, there is a hole in this plate which restricts the muffler, which keeps up
back pressure, that saw is easier to tune, no need to have a tad too much fuel going in
to her to keep the engine from reaching too high an rpm, I use that saw for cutting down trees
and limbing, as running it at differing rpm and allowing it to idle while lifting bushes and walking around
the tree does not result in any un-burnt fuel dripping out the muffler, there is none to do this as the saw stays
at a safe high rpm without having to over fuel it.
Now if your also porting the saw, then that tad of extra fuel required to keep the saw from over revving
if you remove the complete plate and cat, will not be a problem as your porting will allow more air to get
into the engine which will burn that slight smidge of fuel.
The saw with the plate and cat removed is also a good bit noisier, and may draw some unwanted comments.
