I've geared mine (12x1) at 6.2-6.6,Actron brushes,24deg timing,Reedy copper springs bent to 180deg.Motor is very hot after heat but it's fast!! Kr is very fast with good batteries.
For 12th scale: Use less timing and lighter springs.
Iíve found that the sweet sport for timing seems to be around 18-20degrees on a 10x2 Kr can motor. Anymore than that and the increase in heat/loss of runtime is out of proportion to the speed gained. Thatís for 1/10th roadcourse pan car (that would be "Pro10" for you guys outside of the U.S.) on a 200íx100í foot track though.