I knocked off 4 tenths with my port and polished stock heads
But I added the Explorer intake at the same time.
with my "sucky" stock heads I outrun people with Trickflow and afr heads every weekend.
I have had a positive experience, but I dont know if everyone does.
If I were you I would buy some GT-40's I have over 450.00 bucks in my stock heads. You can buy GT-40 heads for that much.
JMO
Later,