Bill...
....see JLC's excellent article on this but, note
an error. Today's pump octanes are given
as PON (Pump Octane Number) rather than
yesterday's given RON (Research Octane
Number).
ADD (not subtract) 2-3 to shown PON for (ballpark figure) RON.
Fr'instance....87PON = (approx) 89-90RON,
89PON = (approx) 91-92RON and so on.
I go conservative and add only "2" 'cause
the difference between modern unleadeds
and the prior leadeds is more than just
lead which, BTW, is a definite compliment
to today's engine and (electronic) engine
"management" technology.
BTW, recommended RON for the original
8.3-1 948 motor was, as far as I know,
94RON, at least 96RON for the later high
compression (9.0-1?) motor, with 98RON
or higher recommended.
Now these are factory numbers so I would
expect them to be conservative, accordingly.
as you can bet they didn't want scads of warranty claims in this respect! :)
Now you can vary from the mfg's recommended timing spec. by a couple of
degrees to run lower or higher octane but
there will be compromises in performance,
fuel economy and/or coolant temperatures
(bearing in mind the cooling system is
somewhat "marginal" to begin with due to
space restrictions).
A lot of this depends upon one's driving style. If you generally "load" the
engine in a "spirited" manner, use the highest pump octane available of course.
The foregoing having been said, today's
octanes are garbage in terms of our older
engines which have no "fuel management"
systems. I'm a real smooooth driver and a"lightfoot" 99.99% of the time but I
would never use anything but hi-test in my beloved street-legal go kart. If
nothing else, the extra .10 per gallon is worth the
peace of mind, IMHO.
Cap'n Bob
Basic Frog
It's amazing how well today's engines run
on today's "garbage octanes". Job well
done by the automotive industry, IMHO.
Cap'n Bob
Basic Frog
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