The gain in octane is up to you. If you tell them you want it to go from 95 to 98 then they'll make a suitable solution up for you. Just be careful with the stuff though, only use it in a well ventilated area as it causes cancer, it melts everything, so try not to spill any (I did once and half my shoe was left melted to the ground.) and never go over 1 litre per every 10 of fuel, put to much in and it will do more harm than good. But do it properly and you'll love it.