More info on the difference between Zetec and DOHC I4 16v. The I4 has a big, heavy block and is very strong whereas the zetec block was based on the cvh block. The I4 has bigger valves than the Zetec, +1.5mm(33.5mm) on inlets and +2mm(30mm) on exhausts and the ports are a lot bigger in the I4 so naturally it will produce more power.