I have discovered this fantastic forum and I have already learned a lot from it. I hope I can do a humble contribution with my messages.
I am the proud owner of an XK120 FHC from 1952 (679882), since this summer.
Even if the car is matching numbers (engine is W5572-8), my current cylinder head is earlier than my car (W3423-7). (This head actually belonging to 679050, information found on from XKdata.com). Unfortunately this head is so old that I cannot put straight 3/8 cam lift on it.
I bought the famous book from Des Hammill that I have just started reading.
My understanding is that a XJ6 3.4 S3 would be the most powerful cylinder head to use.
My questions to you:
Does the XJ6 3.4 S3 also has the big valves (like the XJ6 4.2 S3, but apparently this one wouldn’t work as the cylinder spacing is different)?
Is the inlet manifold also straight port even if it has only 2 carbs originally? Would it then be the best manifold to fit with my twin HS8 carbs? (I have already bought these carbs)
What would be the loss of performance compared to a Triple set of HS8 with a triple carb manifold? (Ideally I don’t want to fit a triple carb set in my XK120 bonnet as I think it’s too crowed and it is needed to cut inside the wing, but maybe I am wrong).
I hope that the modifications needed on the XJ6 S3 head are feasible without too much trouble. My understanding is: Closing the 2 cooling holes - Adapting the old cam covers to keep the old look - Adapting the mechanical drive tachometer to keep my old tachometer - Adapting the cooling system/cooling hoses to keep my original thermostat/thermostat hose/radiator/temperature probe.
Many thanks in advance for your wise answers.