Fox My stock 91 GT performs better on 87 gas

MrPerfect2 said:

When you say “ better grades of premium gas have fuel additives “ are you saying the 87 gas has no cleaning additives in them ? I also heard the generic companies just buy gas from the major refinery companies - I also heard that all gas starts as 87 and they add the octane additive to cause it to be less volatile and bring octane ratings to 93 . Another aspect is that all octane grades share the same hose at the pump , meaning if guy who bought 87 before you then you get about a good bit of the 87 that is sitting in hose . Btw , I am not really that OCD about this topic , just simply chatting on subject - who really know what’s in those mystery underground tanks at the pump , lol .

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Plenty of people do and you can too depending on how interested you are on the topic.

All gas at the pumps in the US contain burning and performance and cleaning additives. Pump fuel with a rating of 89 or higher has essentially the same additive package as 87 with even more additives to increase octane and an altered detergent package more suitable to higher compression burning.

It is a misnomer that lower octane gas ignites easier than higher octane gas. That is only true of ignition by compression and not true of ignition by spark.

The "flash point" of unleaded doesn't change very much because of the additive package although you can find exceptions; Mostly in winter additive packages in colder climates.

Non DOT rated gas is different altogether including things like Sunoco race gas.

Gas all comes from the same refineries really. There aren't that many people making this stuff given the cost of such an operation. Depending on the middleman, certain additives get added to the fuel such as detergents. These are added across the board to all octane levels at a certain brand and the only difference is the octane level.

There are also many other variables that come into play when determining what octane level to run. The general rule is to run as low of an octane as you can run without experiencing detonation. Higher octane allows you to be a little more "aggressive" with compression ratio, boost, or tune because the fuel actually resists burning, but that resistance can also cost power, which is made up by the advanced boost, timing, or CR. It's a chicken and the egg really.

I've always wanted to see a dyno of a N/A car tuned conservatively to run on 87 octane, and then flush it and run 93 octane. My guess if the car with 87 octane would make slightly more power.