See my (old) post
in the CodeMasters forum. No, I think there is no in-game adjustable FOV.
The FOV is in the cameras.xml file for each car. Briefly, you convert the file to text, edit it and optionally convert it back to binary. You need the utility binxml
(from racedepartment.com/EGO engine Wiki) to convert the file.
The website "gridjoint" which hosted the original binxml utility no longer exists. Other GRID websites may still have the original binxml versions. I have a copy of the original archive which I can make available if necessary. I haven't tried the version from the EGO engine Wiki yet. I think the MS-BINXML format for SQL Server is NOT the same format as used by DiRT3.
In DiRT2 it was not necessary to convert the file back to binary, the game was able to read the xml as text. That may not be true for DiRT3, haven't tried it.
The standard FOV for the headcam appears to be 55 for the few cars I've looked at.
Example: <Parameter name="fov" type="scalar" value="55.0000" />
MAKE COPIES of any cameras.xml files before you mess with them!