Originally posted by L8 Apexing Aussie:
Cheapest and best:
Go to a paint supply store and buy a gallon can of Toluene or Xylene, tip that stuff in and then fill up with Premium. Trust me it works. I used to use that stuff on my Turbo Eclipse. It allowed me to run 20psi on stock internals with NO detonation.
The can shoulkd cost anywhere between $7-$10 and you'll end up with a RON# of around 98-100
A can of "Octane booster" will maybe get you to 94! 
and costs the same!Agreed.
The cans of Octane Boost promise to raise your octane by xx "points" - they mean tenths of a RON. Not worth the $$$ IMO. Buy some Xylene or Toluene. I've used it and it works with no bad effects. It's what the refineries use to make the different grades of octane (among other ingredients). My local Home Depot stopped carrying Xylene but Lowe's still has it.
Read my big post in
this thread for the exact math. IIRC, it takes me 2.5 gallons in a tank of 93 to get a RON of 98 (which is quite high anyway). If you can follow the algebra you can determine exactly what octane you will end up with.
