The Mitsubishi engineers initially choose a high octane fuel strictly to meet the parameters of a mathematically derived theoretical stochiometric mixture. When this was shown to be empirically correct, they used their hard-won knowledge to create this amazing vehicle. With the 999cc IL3, these superb engineers dared to push the conventional design envelope beyond what was previously known to work. The 451 was a revolution.
"To reduce friction, the tension of the piston rings
was made 60 % lower than that of conventional piston
rings. To permit the low-tension piston rings to be
used, steps including minimization of the cylinder-head
bolts’ tightening force and deep location of the
bolt threads were taken to minimize bore deformation.
Reduction of the contact surface area of the piston skirts
was also implemented to cut friction. Each piston has a
30 % smaller contact surface area and is 25 % lighter
than a conventional piston with the same bore diameter."
"For combustion enhancement, cooling of the cylinder
head was optimized to permit a high compression
All this advanced technology necessitated a meticulously calibrated and injected fuel/air mixture that would burn evenly and progressively from the initial spark ignition near Top Dead Center, smoothly and as coolly as possible, down to the very bottom of the piston stroke, gaining maximum efficiency out of every drop of premium gasoline and protecting these magnificently-engineered combustion chamber parts from debilitating shock and improperly focused heat. That's what high-octane premium does. Low octane regular blows up all at once, placing more stress on these vital parts and creating higher, out-of-spec, damaging temperatures at critical junctures such as the tiny valve seats.
Thanks to SCoA member "Ptero" for providing this.