John, that's a good point, because I always had the impression, like
you, that the Merlin out-shone the Allison. Both of them are legends,
and I thought it might be interesting to bring out some of the facts now
that it is so easy to find what appear to be solid facts in some sites
on the Internet.
Anybody that's interested can easily look both of them up on the
Unlimited Excitement or the Aircraft Engine Historical Society sites, or
just searching on Rolls-Royce Merlin, Packard Merlin, or Allison V-1710.
Rolls-Royce has a huge website including their Heritage stuff, of which
they are rightfully very proud.
My impression so far is that the Allison and Rolls-Royce Merlin V-12
engines were very much on a par in quality and performance. Both have
the six inch stroke but the Merlin has a few less cubes due to a smaller
bore. They are so much alike that Allison fork-and-blade conrods can be
used in Merlins, since some Merlin people think they are better. The
main difference is that the Merlins have their four-valves with the
stems parallel to each other, and the Allison four-valves have the
intakes and exhausts at 45 degrees as previously mentioned. The Merlin
is wet-sump and the Allison dry-sump oiling. Otherwise, from what I saw
in a short review, the whole engine construction is very similar. Bill
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