There not much you can do other then exhaust mods, can do maybe a airbox mod to get more induction sound.
You could cut open the exhaust and remove/cut away the snake/S bend in the exhaust and reweld in direct pipe.
Otherwise slip on.
2016 - Kawasaki - ZX-6R 636 (ABS)
Rear Wheel 130HP / ~97kw & 53ft-Ib / ~71nm
Mods: Two Brothers S1R Slip-on Exhaust, Decored OEM headers, LED lighting conversion (Headlights, Markers, Indicators), TST Industries Taillight light and TST Industries Fender Eliminator
Woolich Racing ECU Tune w/ Race Tools: Quickshifter, Launch Control & Pit Limiter
Planned Mods: Braided Brake Lines
2016 - Kawasaki - Z125 Pro
Mods: Yoshimura RS-2 Exhaust, Airbox delete with Short Ram Intake with Pod filter and LED Headlight and Markers Conversion