Why are 318's low HP and torque?

Well I got a pair of J heads from my buddy already ported and rebuilt for free so what can I say? 302's are not as easy for me to find in my area. I'm building with what I have right now so It took me in a new direction. If you think that j heads are bad then I'll keep looking but for now this is what I have to work with.

You're saying that you'd rather go with stock 318 heads than j heads?