Be carefull with flowing these heads. If done wrong it can work counterproductive, I would recommend this should be done by a B20 specialist.
Here are some informative sites regarding maintanance&tuning the B20 engines. On the 1800philes site are a lot off very good links, lots to read!
http://www.vclassics.com/archive/index.html
http://www.1800philes.com/