> Scott made some comments on the ancestry of the BMC B type engine.I
> believe that attributing the inspiration of this design to the inline Chevy
> six is a bit far fetched.
I stand by Lindsay Porter's very well researched book, "Leyland B Series
History and Technical Data," Haynes, 1990 or so. If I get time to post
any information over the weekend (I'll be working on a book proposal for
Comdex tomorrow and off to research an article in Napa on Sunday), I'll
try to type in some of the pertinent passages, plus ISBN and other
references.
> Take for example the design of the cylinder head.
> The combustion chamber design in the BMC has the peculiar heart shape,
> certainly not found in the Chevrolet.
No, that was a Sir Harry Weslake bit of genius. Sir Harry really made
some solid improvements in flow, detonation resistance, and other charac-
teristics of the head.
> The explanation may be much simpler.
Actually, it's much more complex... :-)
> When BMC was formed,
> Austin merged with Nuffield ( Morris,MG,Wolseley). If one looks at the ohv
> Wolseley engines of 1939-1940, it is apparent they have many
> features that were later carried into the BMC B-type;possibly these
> engines were designed by the same team.
I'll try to make a point over the weekend to highlight the history.
The B and A Series engines were not exactly plagiarized from the
Stovebolt, but they were descended from engines that had been largely
adapted from engineering lessons learned while licensing the venerable
Chevy truck motor. The head was largely new in many particulars, notably
the combustion chamber shape (as you point out) and the port configuration
(as I mentioned in the original posting). And it's quite remarkable, in
many ways, that the MGB was able to generate the kind of specific output
figures it can with what amounts to a late Forties head on a mid-Thirties
block.
> Lastly it is intriguing to speculate what caused the demise of the vertical
> (downdraft) SU carb found in quite a few British cars of the late thirties,
> including the Wolseley mentioned above, the Lagonda V-12 and
> others.The standard argument, that the piston wore excessively on the lower
> side seems not very convincing.
My own reading, supplemented by a fascinating Fifties-vintage booklet
called "The Sports Car Engine" by someone using the pseudonym "Calculus,"
indicates that it's because of the superior breathing that a side-draught
or semi-downdraught (what the S in HS 4 stands for) carburettor provides
on an engine with ports on the side of the head. Flathead engines often
have ports on the top of the block, and a downdraught carburettor would
be a natural for that, as it requires no serious changes in flow direction
on the way into the motor. As engine technology in the Thirties changed
from torquey, low-compression (4:1 or 5:1) engines with low RPM and low
intake velocity requirements to something approaching a modern compression
ratios and RPM levels, the intake volume and velocity permitted by a
side-draught carb on a side-ported cylinder head proved superior. This
would have little bearing on a V-engined car, such as the Lagonda; but
by the late Thirties, the Depression was the biggest enemy of bespoke
luxury cars such as the Lagonda. If I recall, that nameplate lapsed
for several years between the beginning of WWII and the resumption of
the Lagonda as part of David Brown's influx of cash and creativity into
Aston Martin.
That, of course, is assuming that engineering reasons are valid for
product manufacturing decisions, much less for product purchasing
decisions. And if you believe *that*, I've got a very rare Datsun I'd
like to sell you... :-)
--Scott Fisher
|