ORIGINAL: Gringo Flyer
IMO a 16X8 is way to big for a ST90. I think even a 15X6 is pushing it.
I run a 14X6 MA on mine and get 10300 as well on 5%
I would try maybe a 15X4 or 14X8 but nothing bigger
I recently upgraded to a Jett muffler and saw a boost to 10,800 on a 14X6MA
With a 13X6 APC I am getting around 11,200
I was really hoping to get a bigger boost with an $80 investment in a muffler.
Still running 5%