318 Head on a 340 Question

The 318 and 340 are the same engine in terms of airflow. At least for most of the low and mid rpm ranges. There is .130 more bore, so the valves would have less shrouding. Otherwise, identical. Cammed and built similar, the 318 respondsto the same stuff. I think you will notice your throttle response is way better, and the 318 heads will make more torque below 3000. I think by 4500 or so the ports will become a restriction.