Hi all,
Some boring stuff for you all.
I read somewhere recently that 18V heads had '39cc' combustion chambers
whereas 18G heads had somewhere between 42.5 and 43.5cc heads (according to
Bentley)..
Is that 18V figure baloney? Has anyone out there physically cc'ed an 18V
head? If so would you share the info? I calculate that the 18G HC motor had
a GCR of roughly 8.81.1 (based on 43.5cc heads) and therefore this 18V HC
motor with 39cc chambers would have a GCR of 9.47.1 - thats if the only
change was the combustion chamber size. I've never seen the 39cc in a
Bentley book before but maybe I missed it. The source of this info is
reliable but the calculations don't figure. The same article said the 18V
had a GCR of 9.0.1, this again doesn't calc unless a) there are other
changes - like deeper dished pistons from the normal 6.25cc HC items or b)
that 39cc is plain wrong.. My calcs say a 1cc reduction in combustion
chamber size equates to roughly a .13 rise in GCR in a std MGB HC motor. A
difference of 3 1/2 - 4 1/2 cc's doesn't calc to 9.0.1.
I also read (probably from a list member) that the MGB's rough idle (and I
guess operation) is partially due to the inequality of the combustion
chamber size across all four chambers so I guess balancing these chambers
will help greatly. Comments from anyone who's tried this? :)
C'mon humour my pedantics. <VBG> :))
Cheers,
Neil.
--
Neil Cotty - Sydney, Australia
1970 MG B GT / 1959 MG A 1600 Mk1
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