You will receive no measureable benefit from running 100 Octane race gas in your NA G35 motor.

As the gentlemen noted above the need for the higher octane gasoline will be found primarily in high compression engines, higher than the stock G35. And that means race built motors with very high static compression pistons, and forced induction motors.

Those types of motors develop higher cylinder temperatures from the bigger bang they are generating through the addition of more air and fuel into the cylinder with each cycle, and more power. However, while the parts may be built to take the greater physical forces, and temperatures, it is possible to have the cylinder wall temperatures get so hot that the air/fuel mixture becomes prone to self igniting without the benefit of the spark from the plugs, which of course is timed to occur when the cylinder is located at top dead center ("tdc") in the cycle. If that occurs, then the explosion at ignition point is working to push the cylinder down.....when it still has to go up to continue working with the other five cylinders....and that is a super violent confrontation that leads to the engine literally tearing itself to pieces.

This "pre-ignition" or "early detonation" is addressable in a couple of ways. One is by paying careful attention to the air-fuel mixture in the tuning process, to be certain that the mix is richened by increasing the fuel amount. The leaner the mix the earlier it can preignite. Lean mix is good for clean burn and big bang...but go too far and you get into trouble. Another is to reduce the amount of boost slightly to bring down the generation of heat. Retarding spark a degree or two is not necessarily going to help you here, because you are experiencing a "self generated" ignition from the cylinder temp....the spark never got a chance to fire off that particular explosion. You can add a little bit of safety by setting your spark back for that zone in tuning for the "best" or most powerful set up, but usually the problem is trying to push too much boost for the mix you have at that particular rpm range for that particular fuel mixture.

The problem gets dicier when you consider the very material impact that air temp, altitude, humidity etc can have on combustion in your motor. All of these change the density of the aircharge that is being sucked into and then compressed with the gasoline. Add to that the risk of getting a "bad" tank of gas that delivers a lower octane than what you are tuned for, or you are so engrossed in your cellphone conversation that you accidentally pump in a tank of regular octane fuel instead of premium....and you can readily see that you need to leave some wiggle room from safety.

This is not as clean and precise a world as a laboratory. In the "field" of the real world there is a lot of variability and you have to set yourself up to be well below the razor's edge.....just in case. Using 100 octane on our cars is advisable if you are running turbo and say more than .8 bar...certainly at .9 bar and above...of boost. (it does depend on your particular set up,so these are not numbers you can just apply to every unit...study up on what your car is actually doing, and remember that different turbos are producing different power at different rpms). At .7 bar you can be happy at premium grade octane levels on the JWT 530BB TT, even California's oxygenated 91. This is not a terrible sacrifice. With a built motor and .7 bar you will be running around 400-425 rwhp on that TT. For the street you will not need more than that!! At .9 bar my car is running roughly 479 rwhp and 566 rw lbft of torque, which is right in the zone I want for track days, and of course it is filled with race gas then.

Just remember to double check your boost setting before you put any more fuel in it. There is a temptation because of all the fun and zoom and grins, after a day at the track and a half tank left of rocket juice, to leave the boost on high settings to milk the use of the fuel even on the street. After all, it cost you lots of money at $6 a gallon or more. The problem with that mentality is you run the risk of forgetting when you return to "brain dead" daily driver distractions and fill up. Then you don't waste the three dollar price premium on seven or eight gallons of fuel...but a $12,000 motor rebuild. Then you feel very smart. If you are very much self disciplined and never make such mistakes....good for you. Being old and infirm I make changing the boost down to street levels one of my checklist items as I prepare to leave the track, and then check boost level again (if I remember) every time I refuel. The boost controller is secured in the glove box where it cannot be accidentally touched by anyone.