dude i may not agree with you calling the Ninja 28 unrefined.. but regardless you will love that motor... especialy if you like high RPM HP.. the Ninja 28 is an absolute top end screamer... makes a C6 look tame on top is a understatement.... I would think a 18 th bell would be fine.. for truggy we use a 14th bell with the Ninja 28 for track racing.....when you drive this motor you'd swear it was a giant .21, as the powerband is like a .21 but with 40% more power across the board.....it also has an amazing sound to it ....