Does the Q4 have a baffle inside it or is it a straight perforated tube through the center? I have a GYTR pipe on my WRR and after pulling the end cap and removing the spark arrester I noticed a small piece of perforated plate welded into the center of the core about half way down at a 45 degree angle. It's still louder then I'd like so am thinking of putting a DRD quiet core insert in it.
http://www.dubachracing.com/cart/index.php?main_page=product_info&cPath=1&products_id=40
The GYTR pipe is made by Dubrach racing for Yamaha so it should fit...???
Greg