AH! The valve placement in the chamber. I have a few projects going on at the same time and when I was thinking of over head cam heads I was picturing the head for my 2002. In that head the valvs are accross from each other which helps scavenging during valve overlap. Now that I think of on of the junker heads laying around at my friends shop (the one with the silver 142 with a B23 in it) the valvs are not across the head but in a row like the B20 head. I'm going out on a limb here and say that given a set valve lift, and because of the port shape and angle to the valve, any B21 or B23 head would flow better than any stock B20 head I have ever seen. Don't all jump on me at once for blasphemying, those are just my guesses from what I know about performance engines and what I have looked at concerning these motors.:)

john

PS you can see what I went with in my 145