Are K&N filthers really that great, if so is it necessary that I remove my airbox and re-jet without adding a pipe. I have a blaster and was thinking about doing a few mods before I ride.

 

I would go with a Uni-Filter.

 

You probably would need to rejet your main jet due to the increased air flow that the K&N would give you. Probably one size fatter would be sufficient for just a filter. It certainly is not necessary to remove the air box. In my opinion, which may be debated, the increase in airflow by doing so is not worth the risk of encountering mud or water when you ride, and with no air box you can guess where the water or mud would go. I'd suggest one size fatter on the main, leave other jet circuits at stock settings. Do a test ride on top end for performance & read your plug for proper mix.