Various sources claim that Inlet manifold C.4953 was introduced from engine number W.1251 (February 1950). There are sincere doubts whether this date is correct. I collected some information on this Inlet manifold and wrote it down (see below). I would appreciate comments on the conclusion. Also owners of an (original?) 1950/1951 built XK 120 that have the predecessor Inlet manifold C.2377 fitted, are invited to comment, mentioning the built date (month) of their car.
(Unfortunately I still cannot upload files or photos; tried everything but no success so far).
Jaguar XK 120 Inlet manifold C.4953 for 1 ¾ ” SU H6 carburettors
Inlet Manifold C.4953 had been developed for the October 1950 introduced Mark VII Saloon. A vacuum port at the bottom rear end of the manifold was required for the brake booster of the Mark VII, as were two upper tapped bosses to support the Mk VII Air Cleaner. The same Inlet manifold was also used on the XK 120 that so far used Inlet manifold C.2377. For application of Inlet manifold C.4953 on the XK 120, however, all these holes were not required and therefor plugged with Brass Plug C.799 or a chromed 3/8" bolt.
Jaguar had two supply sources for Inlet Manifold C.4953: William Mills Ltd of Wednesbury and West Yorkshire Foundries of Leeds. They can be easily recognised having different casting marks.
Inlet Manifold C.4953 made by West Yorkshire Foundries Ltd is marked D 180 .
This version has only two brass plugs: one at the lower rear (vacuum port) and one below the rear carburettor (water channel). Some very early versions may have no vacuum ports, not for the (Mk VII) brake servo, nor for the Trico windshield washer.
Inlet Manifold C.4953 made by William Mills Ltd is marked WM 2724 .
This version has 4 brass plugs: one at the lower rear end (vacuum port), two below the rear carburettor and one below the front carburettor. It also has the vacuum connection for the Trico windshield washers.
West Yorkshire Foundries also manufactured the earlier Inlet manifold C.2377 as used on the XK 120 and apparently kept the casting number D 180 when the above modifications in the tool were made and the Jaguar code number was changed in C.4953. This was possible as the overall design of the manifold had not changed and they only had to add the two bottom ports and the top bosses for the Air Cleaner.
We assume that the West Yorkshire Foundries manufactured Inlet manifold was initially intended for the Mk VII as the Mk VII SPC refers to the use of two Brass Plugs C.799. The XK 120 SPC refers to four Brass Plugs C.799 which clearly refers to the William Mills manufactured version. But the Manifolds are fully interchangeable.
Inlet manifold C.4953 was used on the Mk VII with A prefix engines and up to B.2916 over a period from early 1951 (start production) till 1952.
The introduction of manifold C.4953 on the XK 120 is often referred to as “from engine number W.1251” (February 1950). The XK 120 SPC refers to the use of certain Studs after engine number W.1250, but there is no clear relation between these studs and the new Manifold C.4953. These new studs relate to the introduction of the new Water Outlet Elbow, not the Inlet manifold itself.
As the new Manifold was first used during the start of the Mk VII production in early 1951, it would not be logical to assume that it became available for the XK 120 by February 1950 (one year earlier).
Hence, we assume that Manifold C.4953 was introduced on the XK 120 in early 1951.