Tuned Pipes

[WGN FVR]

I was wondering if there are any rules reguarding tuned pipes and racing? I know that ROAR has rules for nitro racing. There are certain pipes that are "legal" and others that are not. If anyone could enlighten me on this I would greatly appreciate it

 

[Bigger the Better]

This is a guess from past readings but yes there are rules and it has to due with exit noise I believe.