Ok I now get what you are taking about, we were still not on the same page till now. When I was talking 125two strokes, I was comparing the cost of running a 250 four strokes to the 125 two strokes, not 450 four strokes. So if I understand you correctly you are running 450 not 250 four strokes? If that is the case then yes the cost would be lower than a 250f, because the motor is not being run as nearly as hard. So your not running against 125 strokes then? Again my ignorance of this sport is showing, but I have been following the European series which seem to be dominated by KZ and have herd little on 4 strokes except for a Swiss made 250 four stroke that was super expensive.
My 450 I ran in SM did require head work at the end of the season that was around the $500 plus a piston $450, not much considering the abuse but it was purpose built, Falicon Super crank, yo yo dyne clutch, 13.5/1 piston, bla bla bla head work. But by the end of the second season it was a lot more expensive. So again if you are running on the same tracks as the 125 karts yes the 450 motors will last longer, but when they do go, and they will go, it’s going to be more money than a 2 stroke.
What are the difference with the new KZ that make it that much better than the K9c? I have checked the port timing, combustion chamber, Squish, even the piston I haven’t seen anything I would consider ground breaking the one thing I did see was the intake track and reed cage but really that would be minimal. Am I missing something?