the K series uses i-VTEC(intelligent Variable valve Timing and lift Electronic Control, I didn't say Honda was good at making up acronyms), a more advanced version of the VTEC used an the B series. This results in more power and better fuel economy. Essentially, VTEC changes the timing and diration of the lift on your intake and exhaust valves based on engine speed (rotations per minute) to maximize fuel economy and give enhanced performance. the Intelligent VTEC system allows the system to have more control through the OBD, which makes use of the O2 sensor to determine what is optimal throughout the powerband. basically, the K20 is smarter and has more options (virtually unlimited, vs. the 2-stage operation of the B-series) and it is also capable of opening up a more direct channel of air flow in the intake manifold to allow for maximum air flow at high RPM's.