I've never found an octane booster that worked to raise the rating more than a few tenths of a point.
I can't say I have direct experience with Torco, but all of the additives have the same basic components.

My best advice - go mix a few gallons of 100 octane fuel into your normal 91 octane fill-up. It'll do a lot more to raise overall octane you than any additive I've run across

BTW the Gas Station on 680 & Andrade road in Sunol carries 100+ Oct at the pump
http://maps.google.com/maps/place?hl...76496029664100

 

Toulene. Most can get it for about $7-$10 per gallon in 5 gallon cans, and it has an effective octane of 114. 1 gallon per 11 gallons of pump 91 gets me 93 octane. It is already an additive in gas, and race cars been running high concentrations of it for YEARS. I believe the old turbo'ed F1 cars used to run upward of 85% Toulene, but my studies of the topic are a year or more old so I may be off a little bit on the percentage.

This information is available everywhere, but here ya go: http://www.elektro.com/~audi/audi/toluene.html

Of course I am now a firm believe in "run the proper octane fuel you want to run." Meaning if I want 100 octane, I will buy it and put it in the tank. If I want more power on 91, then as Mike says "you need a bigger turbo mate!"