There are variations of Duratec cylinder heads: early heads which have a low port design and later heads which have a high port design.
The shot above where you can see the valve guides protruding into the port and the casting of the head raised up around them is the high port version. Effectively the ports are scoped out further around either side of the guide producing the high port design. The shot underneath is the low port version and you can see that the guides in the ports are much shallower, so you can only see the tips of the valve guides. There is insufficient material to be able to modify it to the same shape. The port would break into the water jacket if this modification was attempted.
All the Duratec head performance figures are based on the 2008-on Focus head (high port design). The high port castings numbers which are know to us are RF3S4G and RF6S4E (there may be other numbers but we don’t know what they are, please refer to the photos above). See picture below for where the numbers are printed on the 2008-on Focus high port head.
Earlier heads are likely to produce 10-15bhp less. The maximum performance figures shown are based on using our components; we cannot confirm what your gains would be with non-SBD components. The results should be similar for the 2.0L & 2.3L Duratec, just produced at different rpm. Please refer to our kits for more information.