> Scott Gardner [SMTP:gardner7@pilot.infi.net] wrote:
>
> I have a 1965 cylinder head with the large combustion chambers
> on my 1972 18V engine. As a result, my compression numbers are
> in the cellar. This also causes me new problems when I'm looking
> at pistons, because if I order the pistons for a 1972 engine,
> they're expecting the smaller combustion chambers, so I get a low
> compression ratio. If I order the older pistons that will work
> with the head, I have the wrong connecting rods. Since I just got
> the engine rebuilt in November, I'd like to fix my CR woes without
> buying new pistons or rods at all.
Understood ... I assume that the engine is fitted with the 'federal
market' spec 18V LC (8.0:1)
pistons and that you want to increase the CR to 8.8:1 ... 9.0:1 IMHO,
you will not be able to
remove enough from the head to compensate for both the increased
combustion chamber of
the pre-18v head and the the dish of the 18V LC pistons. IOW, to 'fix
your CR woes' you will
have to fit some combination of new pistons, rods, and/or head.
> Is it possible to shave enough material off of the old large-chamber
> heads to reduce the chamber size to that of a newer head?
ROM ... removal of .010" reduces the combustion chamber by 1cc. So,
removal of 'approximately'
.040" will reduce the 43cc chamber capacity of the pre-18V head to the
39cc capacity of the 18V
head.
> If I can do this, I can just order the newer 18V pistons, and the
> compression ratios will be as advertised in the catalog. If not, can
> I use the older rods and pistons with the old head in a 18V engine?
> I know I can order custom pistons from Venolia, but would prefer
> using a standard part.
Yes ... you can fit either a set of 'the older rods and pistons' or a
set of 'custom pistons from
Venolia'. A set of Venolia 'forged pistons' are approximately the same
cost as a new set of pre-18V
stock 'cast pistons' and used rods.
So ... you have several options ... remove approximately .040" from the
existing pre-18V head
and fit a new set of 'home market' spec 18V HC pistons ... or .. fit a
new 18V head and a set of
'home market' 18V HC pistons ... or ... fit a new set of pre-18V pistons
and a used set of pre-18V
rods ... or fitting a custom set of pistons.
Just my 2 cents worth ... hope this helps.
Safety Fast! ... larry.g.unger@lmco.com
'61 MGA 1600 MkII
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