Mk1 and Mk2 will not fit. These heads are single ports, siamesed internally.
It's the Mk3, Mk4, and 1500 that interchange. These are dual port heads. The
manifolds are quite different in appearance. The Mk3 thru 1500 has two runners
at
each end, for a total of four ports. The Mk1 and Mk2 have a single runner at
each
end, looking like a Mini manifold, I think.
There are at least two different 1500 ZS manifolds that I am aware of. One has
very small passages, the other has larger passages, of the same size as the
passages in the head. I can say that the later 1500 (my 1980 for example) has
the
small runner manifold. Presumably, at some earlier time, the larger passage
manifold was used. This difference can easily be seen at a swap meet by the
blackened ring around the passage on the manifold face. The difference is at
least a quarter inch in diameter reduction. There has been discussion in the
Spitfire group about the performance restriction of this manifold as opposed to
the larger passage ZS manifold, with rather inconclusive determination. No one
has been really willing to spend the time swapping them on and off a single
engine. There are also variations in the drilling of the manifold for various
emissions equipment, but the basic casting shape appears to be the same.
The ZS bolt pattern is different then the SU's. You would have to drill and
tap a
ZS manifold to adapt an SU to it. Or at least drill it and use bolts instead of
studs. It could be done, and I think it has been done. Be aware though, the ZS
manifold design is very poor. It promotes a great deal of fuel drop out, is
highly restrictive to air flow by its abrupt 90 degree turns, and causes
inherent
inbalance between the cylinders by the firing order of the engine (the latter is
also a problem with the SU manifold design).
Be cautious about how much money you spend on a HS2 manifold and carb set. I
got
mine for around $40, so it was money well spent. But spending several hundred
would be foolish, because at that sort of figure, the non-US HS4 manifold and
carb
set can be obtained. Last year I ran into Quantum at Carlisle, and they were
selling the HS4 manifold and carbs for something like $150. You wanted to paw
through the piles of them because some were trash, but very good ones were to be
had this way. So spend wisely.
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