318 Port match heads to Performer RPM Intake

PRH said

bigger than the heads........ and after being corrected has actually resulted in a loss of power.

Click to expand...

Absolutely.
The flow capacity of the stock 318 heads is a major mismatch to the manifold. Signal to the manifold will be very lazy in the bottom end, killing torque.
I would be sceptical even with ported 318 heads..