I've found that by converting to E85 I can save a lot of money and get to get to use pump petrol. E85 isn't that all that easy to buy in the UK yet, but all I had to do was buy a second set of main and idle jets drill them out to 140% of the size and re-time the engine two more degrees BTDC. No more octane booster. Over in the States I read E85 is easier to get , I read some engine builder was getting 10hp per whole digit over stock and better fuel economy too.