Xylene versus toluene for octane improvement?

[ATCO]

I've used 40% Xylene mix with Shell V-Power.

Chose Xylene because it has better RON/MON rating compared to Tol.

Bearing in mind the stuff is not very pleasent to breathe in, it actually works very well as an octane booster/anti-knock. In fact it eliminated knock altogether even when running quite high boost of 2Bar which I would not have risked on SUL alone.

It will not work in low temperatures, anti-knock to the point it won't burn at all! You can compensate by allowing the engine to warm up thoroughly before driving, aided, if you have one, by 'common' heating at the swirl pot. It is not a winter fuel though.

It also is an aggressive substance, so be aware the fuel pump seals might not like it, or your fuel lines.