Before the belly stinger, was it just a hole in the end of the cone? From what I've found, the resistance of gas flow through the stinger is what controls the pressure bleed off rate in the pipe, and therefore is very important. Some restriction is neccesary, but too much will choke the engine. The ideal amount is another variable that can be dialed in to make the pipe preform the best.
When I started, I used some 1/4 OD copper tubing that was far too restrictive. It was very quiet however. That was before the header was at a somewhat optimal length though, and it may be worth revisiting.
I ended up with a 12" piece of 3/8" black iron pipe, the stuff used for plumbing natural gas. It was the most appropriate thing I could find at the big box store, haha.
Later I welded the end shut and drilled four holes in the side of the tube. No difference, even in sound. This setup is pretty loud.
Keep in mind that the tube is only inside the chamber about 1". I figured due to the relatively large diameter it may disrupt the wave if I stuck it in all the way to the belly. Would likely be quieter though.
Currently my engine is all taken apart, I decided to man up and finish balancing the crank before revving the thing to the moon. It amazes me how tough the steel in the crank is, while the rest of the engine is soda cans. Took me a while to grind through it, with a cobalt bit to boot! Think I sharpened the bit after every couple minutes of drilling. JB weld is drying in the holes left behind. I filled in a couple more holes as well, I'm curious how raising the CCR will affect the engine. From what I've read, there could be no low end whatsoever left, but that's ok, jb weld isn't hardened steel. I'll grind some of it out if it's killed the torque.
Logan