Since the published pump octane is the average of two different octane tests, just because the pump say a number you cannot be sure how each tankful will react.
Motor octane numbers are 2-3 times more expensive than research octane to increase.
"Sensitivity – The difference in octane numbers between RON and MON. A high sensitivity fuel would have an MON much lower than it’s RON. This is a general indicator of the sensitivity of the fuel to changes in severity of the engine operating conditions. Standard US pump fuel usually has a sensitivity of 10, so a 92 octane US unleaded pump fuel will usually have an RON of 97 but an MON of only 87.
"In the motor protocol (ASTM D2700-92), the input air temp is maintained at 38C, the ignition timing varies with compression ratio between 14 and 26 degrees BTDC, and the motor is run at 900 RPM. In the research protocol (ASTM D2699-92) the input air temperature varies between 20C and 52C (depending on barometric pressure), timing is fixed at 13 degrees BTDC, and the motor is run at 600RPM.
The motor method, developed in the 1920s, was the first octane rating method devised. After its introduction, many more methods were introduced. During the 1940s through the 1960s one of those methods, the research method, was found to more closely correlate with the fuels and vehicles then available. However, in the early 1970s automobiles running on high-speed roads, such as the German Autobahn, started destroying themselves from high-speed knock. It was found that the difference in ratings between the research and motor method, known as the fuel's sensitivity was important as well. The greater the fuel's sensitivity, the worse it performed from a knock point of view in demanding, real-world, applications.
A MON of 87 may be insufficient for extra ignition advance depending on air inlet temperature.
http://www.crcao.com/reports/r...3.pdfh ... /r...6.pdf