1.311" (33.3mm) dia x 3.57 long intake valve.
Our race valves are produced in EN214N steel and require Manganese/Silicon bronze alloy valve guides. use the later narrow, single collet groove and current valve head shapes.
As it is possible, even common, to swap one head for another on 1275 engines, it is quite easy to become confused,Be aware that if the head has been worked on previously, it may have oversize valves; it may have undersize if seats have been installed.
Unless you are 100% sure what is in your cylinder head, it is a good idea to remove a valve for accurate measurement. There are two lengths used (nominally 3.52" & 3.57") three different collet types, (wide, narrow, and three-groove) and many different head diameters!
All variations of the 12G940, and the latest CAM head castings all use the 3.57" long valves.