This valve timing diagram was found in a collection of papers of John Cooper, who owned a 1929 FWD ("TV100") and later became a prominent motoring journalist. 


It is not known to which cars this cam might have been fitted.  There is no mention of a special cam in the Parts List for the FC type cars that ran in the 1928 Ulster TT.  However, this is a genuine Alvis drawing - the style is unmistakable.