So here are several factors.......The magnum head, stock, is more of a performance head on a 318 as oppose to a 360. The 3.91 bore is not pulling as much into the cylinder so the ports act larger. This allows more RPM on a 318. Also, the valve size per cylinder diameter is acting as a performance valve in the 318 as a 1.92. If you ever drove or owned 5.2 and a 5.9 in the same vehicle (I have), the part throttle response is better with the 5.9 BUT wide open throttle the 5.2 really pulls just as strong as the 5.9. Seat of the pants, really no difference at all. That is because the heads and cam are acting more of a performance part per C.I.