Stinger Starting At Belly Area
I hooked up a microphone to my computer and got these readings so you can visually see the difference
Click here for my video where you can here how quiet it is with the exhaust exiting from a hole in the belly.
Without losing power you can reduce output noise by 50% just by using a belly stinger. I incorporate it into all pipes I make. The more concentrated the sound wave, the louder it is when it exits into free air. That's why we should allow its weakest stage to enter the stinger. This gives just a little boost in the return wave strength (the later part of it).
LONGER STINGER CALCULATION for bigger diameter is on my "various calculators" Excel spreadsheet available for free from www.dragonfly75.com/moto/various.html It's at the top right corner of the spreadsheet.
Here are peoples comments when I posted this info on a forum:
EJ: "friends in the know with dynos tell me a belly stinger that is properly the right length makes more hp than a standard outlet"
CA: "This exact mod is described in gordon jennings book. From what I recall, he observed no difference in HP, but a noticeable quieting of the exhaust sound."
PS: "Olaf Aaen pipes are made like this, I had a pz 480 and a Indy 650 with Aaen pipes, and they did not sound loud, but they had a deep mean sound. And also ran great."
CB: "I have tested this on a dyno. Our race class in the ACU is limited to 105db, I was running borderline 105/106. Moving the point of entry to the tailpipe to the belly resulted in a 1.5db reduction with no changes to performance."
And here's my design for a racing silencer to make it even more quiet:
Be aware that the belly stinger design traps oil in it and so the pipe needs to be removed every few months and gasoline poured into it to swish around and then pour out. Either that or just drill a small pinhole on the pipes underside at the lowest point for the oil to drip out. Due to oil there I doubt the pinhole will relieve the pipe back pressure.