"JGalban via AviationKB.com" wrote

That's what I figured. Turbocharged engines are a different kettle of
fish.
The main reason is the higher temperatures in the induction system lowers
the
detonation margin considerably.

Not just the temp, but the pressures involved.

In a turbo, not producing boost, a low compression ratio is fine with low
octane gas. When the boost is putting all of that extra air and gas into
the combustion chamber, it is still compressing at the same ratio. You end
up with the normal internal pressure, plus the extra pressure the turbo
boost shoved in there. Then detonation becomes a big problem, without the
extra octane.

But you knew all of that, already. g
--
Jim in NC