The Xylene and Toulene "concoctions" were done by a guy who works in the chemical department for one of the Major
oil companies. ie he is in the business. I don't remember where I read it but I think it was on the Buick Turbo web site where the original "recipe" came from. He basically stated that the
oil companies use the above compounds along with MTBE to increase the octane when they need to. Of course they also add other chemicals for cleansing and lubrication.
Remember, virtually all new cars and trucks have the fuel pump (plastic) suspended inside the fuel tank. So the
oil companies have to take into cosideration that fact along with the fact that the modern fuel pump is very small and has to pump a lot of pressure for the Fuel injection. The pump on my Grand National will see 36 psi PLUS what ever boost I'm running. So if its 24 lbs of boost the pump is putting out 60 psi at a very high flow rate. ie its working very hard. And it needs to do this (on a stock motor) for over 100,000 miles. So lubricants and other additives have to be added.
However, for my Cobra that runs 9psi fuel pressure, has an external fuel pump, and will probably see 3k miles per year its a different game.
Bottom line is if your running more than 9:1 compression you need to do "something". You can run race gas. Works great, is expensive and inconvenient for most of us. You can waste your money on over the counter products that will pick you up 3 or 4 "Tenths" of an octane for 4 bucks or so. You can do some mixing like I do. Or you can run alcohol injection like I run on the Grand National. That system is excellent and anyone interested can email me for the system and it is very high quality and proven by a LOT of Buick guys.
That's about the jist of it except to say that if your running any kind of blower/turbo you had better think about fuel as the pistons don't like detonation when on boost. Been there/ done that
Regards,