Actually, Rob, on this one you are incorrect. There is not a "thing" called vacuum, in otherwords some invisible magic fluid, anymore that there is a thing called dark (lack of light) or something in a glass that replaces half full to "fillup" and "be" half empty.
The fact is that the pistons PUSH the air out of the cylinder during exhaust, and when the intake stroke is happening, atmospheric pressure from outside is pushing air into the empty, evacuated cylinder.
We talk about "suction" but in reality there is no such thing. What there REALLY is, is the atmospheric air pressure pushing into a void, an evacuated space.
But the more important point is that a reasonably "big" manifold such as a street 340/360 works well on small port 318 heads for a good solid performance "bolt on" jump.
These little guys DO also need a bit more cam, and of course exhaust as stated.
It's really too bad that "Ma" didn't make these engines more easily interchangeable, AKA 360 heads on a teen.
