The other change in 1970 was the switch to the "dog-leg" heads. These heads flow 20% better on the exhaust side than the 1966-1969 rectangular port heads and are thus the best for performance. There are two reasons for the flow increase: (1) the area of the port is larger, due to the dog leg and (2) the shape of the port floor was changed from a concave to a convex curve. The concave floor tended to bend the exhaust flow upwards which caused turbulence when the flow was forced to go down into the exhaust manifolds. By switching to a convex floor the curvature of the flow starts in the head and proceeds much more smoothly into the exhaust manifold resulting in less turbulence and better flow.