one thing i noticed about a a few of grp plugs was that they took a few times to work correctly, u would have to fire the engine up a few times before it would start acting correctly like the plug had to be broken in or something, i had a few that lasted a long time and i had a few that would just never work good, could just grab another grp plug and put it in and it would run good then just put the other one back in and it would do the same thing, if you allready have the os plugs it would be crazy to buy the grp ones, i did find the ninja grp 5's for around 8 dollars a piece when they are on sale, but i just would use the os plugs