carbs from a 1968-71 XJ6,
From the tag, yes, slightly later than 69 I think because the ASC feed lines are not curved tubing like mine, but straight with banjo fittings.
the cams are four bolt so I assume they are the later XJ6
I think so. They might match the head, my 69 seems to have just missed the introduction of the new cams, I have the old design.
and the block has a plate in the back of the water jacket so again I am assuming later XJ6,
The block is ribbed. The earlier blocks weren’t ribbed and didn’t say British Leyland either.
the valve clearances vary between 7 and 15 thou, I did read that you can run tighter clearances on the later cams and get better overlap / lift, was thinking of trying 8 -9thou, has anyone heard of running this sort of gap?
I don’t think it’s a good idea, someone explained that the valve stays seated for a shorter period due to the ramps with the parabolic cams - and it won’t do much good anyways, at least what I think. Do you have the big valves… not sure. This being a 3.4 I don’t know anything really. I’d set them to 12-14 and forget about them.
The 3.4s never had injection, but some HIF carbs or so. Someone probably put the good carbs and inlet on the engine as it was. One clue is the lift brackets on the heads, and the ignition wiring cable mount, I think they were introduced later? Did someone paint the head?
Both correct assumptions: anything it’d buy in performance would likely eventuate at high rpms, not a place you want to live w/o serious blueprintings and mods.
This is somewhat related to what Ed Iskenderian once said, when someone asked, “What cam should I put in my car so that I get the best all-round performance on the street?”
Ed didn’t miss a beat: “The one the factory put in it.” Same for clearances.
Ed knew a thing or two about camshafts…
The ports in the head look quite large, I had to take quite a bit out of the earlier manifold that it came with to match the ports, 3-4mm in places, the manifold ports were generally offset to the head,
Does anyone have series3 parts books? just wondering if the 3.4 and 4.2 had the same head / valves, tried looking on the SNG site but they don’t offer many series3 parts.