If you have a 100% cylinder fill at sea level, you will have 14.7 psi in
the cylinder. If you multiply that by your compression ratio, you can come
up with what your cranking cylinder pressure should be if this were a
perfect world, which it ain't. Figure 80% of that for an engine in good
condition. If you are at high altitude, figure 70%.
Example: 14.7 psi x 8.2 = 120.54. Multiply that 10 fold for combustion
pressure. If that figure exceeds the anti knock index for the fuel you are
using, combustion irregularities may occur.

Dirty little secret is that often you dont get what you pay for. Its common to substitute lower octane and 90% will not know the difference.
But the 10 % who actually need the octane will.
The state checks volume but not octane levels at least here
Its also common to have independant stations buying non branded gas- So what you were getting wasnt nessesarily ammoco because it was an ammoco station.
Had a relative who was an ammco distibtor in FL for many years

Not long ago we had a local station get busted. The owner would order mid grade and have the driver drop most of it into the premium grade tank. This is more common than one might suspect.
Matt

In the late 1980s, automakers became concerned with fuel additives as more advanced fuel injection technology became widely used in new cars. The injectors often became clogged, and the problem was found to be inadequate levels of detergent additives in some gasoline. The automakers began to recommend specific brands of gas with adequate content to their customers. But some fuel marketers were still not using detergents, and in a move supported by the auto industry, the federal government mandated specific levels of additives. The U.S. Environmental Protection Agency (EPA) introduced the minimum gasoline detergent standard[14] in 1995.

However, the new regulations had unintended consequences. The new EPA standards required lower levels of detergent additives than were then being used by a few major fuel marketers. When the new regulations came in, most gasoline marketers who had previously provided higher levels of detergents reduced the level of detergents in their gasolines to meet the new standard.[15] The EPA detergent additive levels were designed to meet emissions standards but not engine longevity standards. Automakers said they were seeing persistent problems such as clogged fuel injectors, and contaminated combustion chambers, resulting in higher emissions and lower fuel economy.[16]

By 2002, the automakers said their repair records suggested that the EPA standard for detergents wasn't high enough, but the EPA was not responsive when they asked them to increase the standards. These concerns were heightened by plans to introduce a new generation of vehicles that would meet the EPA's "Tier Two" environmental standards for reduced emissions. These vehicles require higher levels of detergents to avoid reduced performance.[15] Cars with direct injection technology (GDI) have been especially prone to carbon buildup, and car makers recommend fuels with higher detergent levels to combat the problem.[17] At first GDI was mainly available in high-end autos, but it is now being used in mid-range cars and economy cars, such as the Hyundai Sonata, Ford Focus and Hyundai Accent.[18][19][20]

In 2004 representatives of BMW, General Motors, Honda, and Toyota got together to specify what makes a good fuel. Using recommendations from the Worldwide Fuel Charter, a global committee of automakers and engine manufacturers, they established a proprietary standard for a class of gasoline called "TOP TIER" Detergent Gasoline The new standard required increased levels of detergents, and restricted metallic content. Volkswagen/Audi joined the group of automakers in 2007. Gas brands can participate and get a TOP TIER license if they meet certain standards, which includes performance tests for intake valve and combustion chamber deposits, fuel injector fouling, and intake valve sticking. Additive manufacturers pay for the testing, the cost of which varies from year to year, while gasoline companies pay an annual fee based on the number of stations it operates to participate in the program.[21]

In addition to higher detergent levels, Top Tier standards also require that gasolines be free of metallic additives, which can be harmful to the emissions control systems in cars.