Bigger valves, better overall head design, stronger components, iVTEC, and MORE DISPLACEMENT! (insane laughter insues)

Remember, the weakest of all the K series engines (K20A3) is 160hp, and it only gets better from there.

The K-series is a 100% improvement over previous Honda designs. The B16A is a great engine, but remember, the design is 16 years old (it was introduced in '88 as an '89 model in the Civic and CRX SiR) so Honda has had plenty of time to improve over it. SCC had a great article a while back about the advantages of the K.

Cheers!