Ive been doing research about the Fiesta ST since it was released in Europe.
So having a 4-2-CC-1 header system as opposed to running a more usual 4-2-1 system will result in better flow? I think not. It has been shown many times in the UK that the exhuast system is a rather large restriction, take a Look at milltek who got a 21Hp gain from a k&N plus exhuast. A 14% gain is very healthy for N/A tuning and this across the board not only up top as you would will a cam.
Im not saying getting new cams won't give you a power boost as it will. But letting the engine breath better will give the best result and will allow you to better match the cam to your needs. If you get a cam first and then get an exhuaust you run the risk of later finding out that youd rather a more agressive cam and have to fork out even more cash.
The
ECU will adjust to the new condition but it will be a very rough and will run rich and may even just into limp home mode.
Lets also have a look at the the Cosworth tuning kits for the 2.3L (Which is very much the same engine). Tuning kit 1 Is a new Cold Air intake and Intake manifold and tune, Tuning kit 2 is a New exhuast manifold, larger throttle body and new cams. If there was more to gain with just a cam Cosworth would have done it to Tuning Kit 1. Going by that it would seem that the intake is the main thing to improve on the duratec (2.3L atleast).