The D15Z1 head was a very bad decision for the previous owner to use. The 'Z1 head is has a VTEC-E system which is very different then the normal VTEC. If it is not being activated, which the PM6 ECU will not do by itself, you are only running on 12 of your 16 valves. The other four are opening just enough to prevent fuel pooling on the top of the valve. The 'Z1 head also has EGR passages cast into it, I have no idea what he did with that.

I would strongly suggest that you to put a normal D16A6 head back on that engine or do some serious rewiring to get that one to work right.