Muffler mod on Echo cs 2511t - Need advise

I want to modify my Echo cs 2511t. Mainly just opening up the muffler but I want to know more than just drilling random holes.
How do you know what size hole to make without over doing it?
Is there a ratio or rule of thumb to follow such as, the new hole should be 50% as big as the original factory made hole?

Thank you in advance

 

If you search for the Exhaust Port megathread, I'm actually breaching that topic right now. If you're only doing the exit on a 2511t muff just copy what Duke / pre-made ones are using (please resist the urge to drill-through the baffle-wall that is behind the exit hole, doing so short-circuits the entire muffler)

If your muffler has a catylitic converter you'll need to look into removing that for optimal flow. On all 2511's you can greatly increase the smoothness of that 90deg entrance into the muffler but wouldn't advise this if you've never done any port work it's too easy to get metal into cylinder doing this..

On mine I left the stock exit pretty much un-touched, instead I made a new exit-hole on the left side of the front-face of the muffler, I did it here so I could access the (3) holes in the baffle wall that the gas passes-through to get from the rear portion to the front, am planning to seal that exit up and simply enlarge the OEM more (once I find a good way to fully seal it, I don't weld :/ )

 

How I did mine

 

The quick and dirty way is to drill a 1/2” hole in the center of the muffler area that the plastic muffler shroud doesn’t cover. Basically where @thinair’s pipe sticks out. You definitely DO want to drill through the internal baffle. The baffle is much thicker and harder than the outer shell of the muffler.

It’s certainly better to add a larger outlet deflector with a large hole under it, but it’s 10 times the work. @Red97 sells a nice cut-to-fit deflector for 2511t if you want to go that route.

In both cases, it’s easy to aim the outlet slightly off and melt the plastic muffler cover.