I have been running a new Sirio CL7B STI.. very powerful motor, feels more like a 28 then a 21 as far as torque is concerned, but it still has a great .21 feeling top end........... I just started running the motor so I have no idea of long term reliability..but by all accounts so far this is one kick ass engine...... I believe its the most powerful offroad .21 yet...or at least according to its dyno results...1.8 HP and 70 oz/in on the X-Dyno