400hp 318

Personally I like the 302 casting heads with 1.88-1.60 valves or magnum heads on a 318. With bigger valves you will lose your port velocity. A 318 will make more power than a lot of people think, and you can do it fairly inexpensively. I built one for a 73 Dart that I had and it ran very strong. The key is definately flow, that goes for any motor. I have found out that just hogging out a port on 318 heads will actually lose power, compared with stock ports. So you need to know a little about what you are doing.