So I iwas really bored and decided to do some research into aftermarket exhaust. So I only got as far as the M4 line wich as far as I can see is one of two aftermarket systems that I can find for the Hawk.(That is new and I can actually order) The other one being D&D which is all over ebay but it appears that they are no longer being made since their web site does not list them.
I found this info on the M4 site where they show a Dyno chart for their pipe and the stock setup on an NT650.
Box Stock H/P=59.3 TQ=38.1
M4 Full System H/P=60.8 TQ=39.9
That is an increase of H/P=1.5 or 2.5% gain
Increase of TQ= 1.8 or 4.7% gain
Now I do not know if they just bolted their system onto the Hawk and did not touch the carbs or if they did do any carb adjustment???? That i do not know and that could be good or bad depending on what they did for the test. It would be good since if they just bolted on their pipes and stayed with the stock Hawk carb settings their might be room for more gains in power and it shows that their pipes produce more power than stcok but it is bad if they did adjust the stock setup to produce as much power as possible on the dyno becasuse the number do not reflect the reason to spend $500 plus on an exhaust system.
The torque curve looks good for the Hawk between 3500 and 6000rpm with the M4 exhaust and that is where most of us use the bike but the overall numbers in my view do not justify the cost. Yes, I do not have to buy them.
As I said I was really bored????????????