A few notes: I think the PI heads (2V) are BIG for a 4.6 and
the flow is not that high for the "apparent" port size. IMO (and
verified by a big-time shop I talk with) the older 96-98 2V heads
are better suited (fully ported) for a 4.6 than the new bigger PI's.
When a Blower is added, the new PI's are really sweeeet
For 4.6 using PI heads I'd be rather conservative
on the porting, they have huge ports (lower velocity) and are really a
5.4 head, it's a universal application head for both engines.
You want porting that has the smaller ports, unless you are going
with a high-boost SC application, positive-displacement blowers
can use the bigger stuff while centrifugals work best with heads
that are ported more closely to NA specs.
A friend of mine is an R&D manager in a big shop and they were
getting better results with 96-98 2v heads (ported) over the
PI stuff, way better matched as far as port volumes go, I think
it was RWHP they were testing and it exceeded 400 BHP
relatively mild camming (~224*) and older 96-98 heads. But
their porting guy is first rate, and their shop is rather advanced.
In short, if you have a 96-98 GT and want more NA power, don't get the
new PI heads, get yours ported! It will be cheaper and easier, and another
hot ticket is use the PI cams, they are cheap and make great torque.