In reply to a message from PeterCrespin sent Mon 20 Aug 2007:
It depends on how you’re doing it, and there are a couple of
options here. Last time I had a set of pistons made, it was $1400
for pistons with ceramic coating, rings, and wrist pins. In other
words, a complete setup.
Now for rods, you can purchase custom rods, or you could go out and
buy some 6’’ Chevy rods. You can find forged H-beam variants of
these, probably under $500. When you get your custom pistons made,
have them use a Chevy wrist pin (which won’t add to the cost since
they’re custom pistons anyway - if anything it’ll decrease the
cost). Only catch here is that you then have to grind the crank to
make the rods fit (2.1’’ Chevy rod journal vs. 2.3’’ Jaguar rod
journal). If you offset grind the crank, you get some extra
displacement out of the deal (just make sure to factor this into
your wrist pin position of the pistons). While you’re at it, you
can always have the liners bored out, Roger Bywater told me they’re
safe up to 94mm. Suddenly, you’ve got a larger V12, and the total
cost is probably more along the lines of $3000-3500, depending on
who you go to for all of this work.
In my case for my upcoming engine build, I think I am just going to
leave the rods and crank alone and stock, and just put in custom
pistons, leaving the bore stock. Since I’ll be boosting the thing I
want to keep as much strength in the materials as possible, and
plus it saves me that cost of doing all those extra little
things. 
From a power perspective, there’s nothing wrong with a stock set of
V12 rods. They’re quite strong. The issue comes in terms of weight,
as they are also very heavy. I would even say you don’t really need
forged pistons unless you’re running some really high power levels
and/or adding boost. Forged pistons have some disadvantages,
specifically that the pistons have a different coefficient of
thermal expansion than the rest of the engine, so they run higher
clearances when cold. This means your motor will rattle a bit when
it’s cold, and you’ll really want to let the pistons warm up some
before you drive the thing hard. I remember hearing Bradley Smith’s
car start up when it was cold. First off, hearing his car start up
was quite impressive in and of itself because of all the gizmos and
such that it had on it, but when it started up you definitely could
hear the forged pistons rattle a bit until they got warm.–
-Ted – '92 XJS V12 5-speed
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