[Healeys] High Octane Gas

[Harlan Polk]

Fred,
Adding to Kees' and Bob's comments.
Don't advance the ignition timing so far that the fully developed burn
maximum combustion pressure point is advanced too close to top dead center.
If so the pressure will beat up the piston top rather than push the
crankshaft throw down. Reciprocating engines are pretty consistently
optimized when maximum combustion pressure occurs at about 15 degrees after
top dead center-it's a matter of the crank throw moving to be offset enough
to generate leverage (torque). With high octane (hard to ignite and slow to
burn) gasoline with stock dynamic compression (stock static compression and
stock intake valve opening and exhaust valve closing) it may be possible to
advance the ignition timing beyond the maximum torque point without creating
pre-ignition.
Excess advance also increases the early combustion pressure that the piston
has to work against to come up top dead center.
A dynamometer with knock sensor is the best way to find optimum timing for
your engine. The challenge with 110 octane gas used in a stock engine
designed for 92 octane gas is that the engine's character is out of balance.
If you significantly increase octane, you would be well served by balancing
the engine's character to take advantage of the gas's characteristics, which
would include resetting:
* the static compression ratio,
* the intake and exhaust flow affecting the dynamic compression ratio,
* the burn time influenced by combustion chamber surface to volume ratio,
its turbulence, its spark plug position, and
* many other factors. 
Of course intake and exhaust systems including carburation should match
these characteristics, as should cooling and block and head stud strengths,
etc. 
Balancing all these elements, along with optimum component selection, and
first-rate build practices is what creates an optimized engine. An engine
with well-balanced characteristics feels right, functions right, and tends
to have a flatter torque curve--smiles ensue.
Can you see some power improvement with higher octane gas and more ignition
advance? Likely, yes. But you would gain much more if the engine were
sensitively built with the high octane gas in mind.
I concur with Kees' comments regarding ignition timing.
I concur with Bob's comments regarding cost and benefits.
The cost/benefit ratio may not be adequate for you using 110 gas in a stock
engine. However, it might be fun to try on occasion. A quality engine
rebuild with mild cam upgrades and a good three-angle valve job as Jonas
suggested would likely bring you more smiles and a reasonable cost, more
responsive engine for everyday driving.
Hap