there is a long thread over at the YZ forum about "the loudest pipe", mostly about land usage. i have been doing some exhaust changes, trying to find a quiet off road setup. my setup - stock headpipe and a 17" fmf ti-4 with a quiet core insert. i have tried the 14" ti-4 with the quiet core but the pipe feels restricted, with the 17", the quiet core doesnt restrict the flow so much. the endcap is the same on both pipes but the 17" runs so much better. the only reason i can see is that the 17" has more volume, and that lets the exhaust expand in the pipe before coming out the endcap, giving a less restricted feel. having said that, the 14"/quiet core setup is quieter and more restricted than the 17" setup. with the pipe companies trying to make quiet pipes, why dont they experiment with more pipe volume? maybe this is the way to get rid of some noise while making the bike feel less restricted?