Most basic engines typically dont use the higher octane. High compression or high performace engines with knock sensors will.
Running on lower quality fuel the EMS will retard the spark - retarding performance.
Also - Petrol quality varies greatly from place to place. Octane 'evaporates' with storage - this is a *fact*. Low turn over sites when tested were THREE to FOUR octane lower than the in -town sites with high turnover, and they were one to two octane below (R/M)*2.
For best quality race fuel, ask the distributer when they will be delivering petrol to your area on the day before your race... Tell them its for racing - they understand. Then go to the garage, and ask which is their lowest level high octane tank and what time delivery for that tank is. Then arrive with the delivery truck. Then you will get the high octane fuel you have paid for!
( and my fuel was tested by the scruteneers at Littlehampton immediately after the race, and it was legal!
) It was also very very fresh, less than 36 hours old!
Some things to remember:
Some petrol has a higher calorific value than other petrol of identical octane. This will give more power in every instance. It may be better to run a lower octane petrol of higher calorific value if you are not going to benefit from high octane.
Some high revving cars will not benefit from high octane
Tuning your petrol to suit your car/engine *will* give you more power than just choosing one supplier. For example, filling 20 litres of TEXACO 92 and 10 litres of TESCO 99 will give you 94 octane, but with a higher calorific value than most standard 94 octane pump fuels!