Over all i like this i just put then in my 2007 Hayabusa. It improve my throttle response and i can feel a bit more power on my bike. Now i wanted this Velocity stack becouse Factory pro says it will add a nice growl to your intake. well no new sound it sounds the same as it did before I added the stacks. I emailed Factory pro about this. They said try a higher RPM to get the sound im looking for. I then re emailed them and said I pushed my bike to 9000 RPMs but no change. There reply was " Try a higher RPM and a higher gear like at a drag race." So they were no help. If you want a little more HP on your bike then buy this like 5 to 8 more HP. If you want the sound that Factory pro said you will get out of thes velocity stacks then save you money. Over all I like them and will keep them. p.s. my bike is a 07 Hayabusa stock with a K&N filter before the velocity stacks.