Joe,
RE:"Regardless of how it is achieved, (Domed pistons or Shaved
head), 12:1
compression will always require the same octane rated fuel to prevent
pinging. "
Sorry, Joe, for once I disagree with you. Combustion chamber shape
plays
a tremendous role in how well a given compression ratio stands up to a
given octane
fuel. Flame propagation varies quite a bit with shape and "squish area"
which is part
of the reason you can buy a modern high-performance motorcycle with 11:1 CR
or more
and run it on pump gas with no problems.
In the case of the Spitfire, I think (but cannot prove) that it
would be far
better to get dished pistons (from the 7.5:1 cars) and shave the head to
achieve a given
CR than to install the flat-top pistons and shave the head less. I'm
familiar with your 250
psi compression horror story, but I ran my old MG Midget 1500 (Spit engine)
with a
radically shaved head and no problems on premium unleaded except dieseling
after shutoff.
Best Regards,
Tom Marincic
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