['ol Pinion head]

Following is a response on the Net, question posed on quota.com

Ryan Carlyle, BSChe, engineer at an oil company
Answered 9 years ago.....
Originally Answered: What happens when tolulene is added to the gasoline in a car?

"Tolulene is one of the higher-value molecules already in use in many gasoline
Blends. The main benefit is that it's an octane booster that does not dilute the
energy content of gasoline like ethanol does. It's a C7 aromatic molecule, which
means it contains a lot of energy and vaporizes easily, but not so easily that it's an
air pollutant like lighter benzene (C6 aromatic) and butane (C4) molecules,
which percolate out of unleaded gas tanks and contribute to smog.

The tricky thing about adding aromatics is that the total quantity in your fuel
shouldn't exceed about 30%, which is the sum of all the benzene, toluene, and
xylene put together. Many regular gasoline blends already contain significant
amounts of aromatics -- up to 30% -- so there's no simple way to tell how much
more you can safely add. as it happens, the higher quality gasoline blends (which
supposedly includes Shell and Chevron gas but don't quote me on that) already
contain a lot of toluene and xylene. Adding toluene is more likely to improve low-
octane gan than high-octane gas.

A rule of thumb floating around the Internet is that you can safely add 10% toluene
to your gas without causing nine issues. So that would increase your 93 octane
gas to (93 * .9) + (114 * .1) = 95.1 octane...."

Not including his last paragraph as he just warns about buying higher octane fuel that's not needed...

Noted 3 paragraphs above it clearly states, how does one know how much of the these aromatics are in the particular (EPA region required) blend of unleaded 93 octane fuel? I ran into this threshold 30 years ago with xylene content octane boosters (tall can of Super104). I'm sure Commiefornia has multiple different regional required blends of each octane fuel to meet EPA attainment (AZ had the most, at least 7-8 years ago). Thus the blends will differ to a degree across the state & even in the same region.

Mixing example wise, one would need to take 1.8 gallons of toluene & add it to 18 gals of 93 octane unlead to raise the pump octane to the above 95.1 pump octane on near 20 gals of fuel. To me it makes little sense to pay through the nose for 18 gals of 93 octane pump gas then add $20-40 expense of tolulene. Building a cast iron headed street engine for slightly lower compression makes one H of a lot more sense.