For me 4th seems weak up high. Mid range feels great. Not sure if its a lack of flow in the head, or a lack of fuel because the mods
I also contacted Akrapovic directly and received this reply:Just a FYI, got this back from parts unlimited
"Hello Thank you for contacting Parts Unlimited
We do not offer any exhaust from Akrapovic for this model motorcycle yet.
Thank you again
Parts Unlimited tech support"