Cross Bike Muffler Modification
First, remove the mufflers (obviously). Look into the INLET end and you’ll see 3 tubes sticking up that flow into the muffler’s inner chamber. Between each of these tubes drill a 3/8” hole using a drill bit extension and a 3/8” drill bit. You can go up to a ½” if you wish. BUT, most importantly, DO NOT drill thru the center baffle. Drill the holes as close to the outside wall as possible.
The muffler diameter is 4 inches. Get a drill bit, either a 3/16ths or a ¼”, and mark the depth to drill at 3 ½”. You want to drill thru the inner tube but not out the other side.Then starting at the rear of the muffler and working your way forward, drill holes STRAIGHT THROUGH about an inch apart. As I recall the plug/baffle is about 15 inches from the front so don’t go beyond that. I put 12 holes in mine (you get 2 holes in the inner tube for every hole you drill thru the outside) that were a ¼” in size.
Now all you have to do is plug the holes drilled thru the side. I paid a local Machine shop $20 bucks to mig weld them. I’m sure J.B.Weld would work or use a short pan-head sheelmetal screw – maybe both.
These ended up sounding almost identical to the Stg 1 pipes. I think it might leave a little more tq. under 3k as well. Sounds much deeper than just drilling out the plug too.