JX .21 hands down
awesome drivable bottom end power, use a JP3 or 2060 and you have a lethal combination, this set up van be ran on small indoor tracks or bid fast flowing track's, it has OS tuning and reliablilty, and 5 ports and ceramic coated crank, runtimes with the mentioned pipes are 10 min plus, the motor is just wicked fast when you want it to be, and smooth when you want it.