Dave,
As you have discovered by your research, this is not a simple question.
Even what is specified for an engine does not always match its true
octane requirement because there are so many variables, including wear,
engine deposits and driving style. Another complication is that the
octane tests used by most oil companies are not done in test engines
anymore, but are predicted from chromatographic or mass spectrographic
results or are done with inline analyzers that use a related measurement
that is correlated to octane.
Then you have the basic Research method and Motor method that are two
variations of the way a test engine is set up. The posted octane is an
average of the two, at least in the US. In some engines, particularly
older ones like a TR3, the Motor method has more relevance than in
modern fuel injected engines.
When I worked for an oil company setting up gasoline blend formulae, we
always had customer complaints that their car would not run well on the
octane grade specified for it. Fleet testing shows that there is
significant variation among the same production engines, although that
is not as significant now as it was when TR3's were built. That is one
advantage of emission testing. On road testing is the only real method
that works, and it is best to do your own. I assume you get no knocking
or valve pinging on premium gasoline in the Toronto area. If that is
true all year, try the next grade lower. Hard acceleration, uphill on a
warm day is the acid test, particularly low on the torque curve.
After all this gibberish, the short answer is find something that works
and stay with it. The occasional ping is tolerable, but if consistent
can be damaging. I seem to do fine on 87 regular, but must back off the
throttle under some circumstances because I get a ping. I am planning
an engine rebuild on my 1960, so I am a little cavalier about it.
Glenn C
1959 TR3A TS31684L [in total frame up restoration]
1960 TR3A TS64803L [driving, but needs work]
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