The 1.6 litres engine in 416 is developed from the 1.4 K series by enlarging the internal bore of the cylinder block. Since the external block dimensions has not changed, other components can be carried over without modification. Of course, you cannot expect class-leading power and smoothness from such a small budget design.
420 uses a T series engine with 2 litres and 136hp. It has better performance, of course, but the engine is not refiner than the 416. This car costs as much as a Ford Mondeo. Therefore 416 remains to be the value choice.Source -