It's my understanding that it won't help or hurt the engine to use gasoline of a higher octane than that recommended by the auto mfr. The detergents used in gasoline is what helps keep the engine clean, and gas companies use the same type/amount of detergents in all octane levels. Using a higher octane fuel than mfr recommendation will not help keep your engine cleaner.

RainMeister
'04 G35C 6MT, diamond graphite, premium, nav, aero

 

The octane rating in gas basically indicates it's ability to not ignite under compression. Octane plays a part in all engines, some more than others. Since the G's engine is equipped with variable ignition and valve timing, the computer will always compensate for variances in air fuel density and fuel quality such as octane.

My guess is that the engineers designed and built the motor chiefly to run on 90/1/3/ octane. However, the engine management system will "compenstae" if a lower grade of fuels (89) is used...probably by retarding the timing. Retarding the timing will most likely occur if the engine management system detects a ping or preignition. This is a paramount prinicpal when using compression adding equipment or technology such as Nitrous or Super/turbocharging.

Going the other way, the engine and managment system has an ideal full advance timing set along with air fuel mixtures that result in it's advertised power rating. By giving the engine fuel that is harder to burn under moderate compression, and without the engine adjusting to compensate (advancing the timing greater than designed or manipulating valve timing) you will not see any gain...in most cases as stated....you may see decreased performance.

Typically 100 or 114 octance race gas is used in high compression engines where the combination of cam and piston compression along with timing require it to run correctly. It can also make a difference when running power adders that are basically compression creators such as a supercharger/turbo or Nitrous.

 

Octane mixing is not a linear equation.
I read years ago in either Hot Rod or Car Craft that if you mixed 1 gallon of 100 octane with 9 gallons of 89 octane you will get 95 octane. Now, you have to consider the time was 1982 or '83 and if you level down to 87 octane we're probably talking 93.5-94 octane after mixing.
They called it the "poor man's race fuel".


JD
2003.5 Coupe, Blk/Blk

 

If I remember my high school auto shop course correctly (been a few decades) octane ratings relate to the temperature at which the fuel/air mixture will detonate. Higher octane fuel detonates at higher temperatures. Even absent spark plugs, compression of fuel/air in a cylinder greatly raises its temperature, so too low octane fuel under too high compression will detonate too early (before the piston reaches the top and the spark plug fires), which is called "pre-ignition" or pinging. That's why higher compression engines require higher octane fuel.

Taken to an extreme, a warmed up engine with low enough octane fuel will keep running after its ignition is cut off simply on the engine's residual heat and compression of the fuel. This often occurs in old engines with buildup of deposits in the compression chamber that reduce the chamber's volume, which effectively increases compression. Shut the key off and...it keeps running. It's commonly called "dieseling"

Diesel engines rely on (relatively) ultra-high compression ratios (about double that of gas engines) to operate normally. That's why spark plugs aren't used in them (they do have "glow plugs", but only to raise the combustion chamber's temperature when they're started cold), and fuel has to be cut off for them to stop running.

 

All information I've read on the subject says that mixing octanes is linear, a straight average of what's mixed. The 2nd graph on this page illustrates the fact. You'll have to whip out the calculator to compare but it works out.

 

Go to an airport and buy 100LL for $2.25/Gal.

If your new cars are pinging with anything from 89 or better, I assume something else is wrong.