The octane rating, which down here is usually 91, 95, or 98, does not equate to the amount of energy in the fuel, it's how much compression the fuel can take before it goes bang -
http://en.wikipedia.org/wiki/Octane_rating
Apparently the 95 here burns better than any of the 98s, so I run 95, and seem to get tens of kilometres further on a tank of 95 compared to running 98. Given that 95 is heaps cheaper than 98, and gets me further, I do my utmost to feed her that. I can't find the bookmarks that I thought I'd saved, but I have researched the topic before and some places did find more calories (or whatever) in 95, but again individual fuel suppliers can differ. Certainly in the case of petrol "more expensive" does not always mean "better", and it's worth trying 95 if you usually run 98, and vice versa. If I recall correctly the handbook suggests minimum 95 rating, so try a few tanks of 95 and report back? Just don't put any of those horrid E prefixed high-Ethanol fuels in, these old fuel systems are not designed for it.
Running 95 I frequently find that my 10 year old rap can leave dukes that are larger and younger looking rather sad, really pisses them off!
![Twisted Evil :evil:](./images/smilies/devil.gif)
Road racing's where it's at - going round in circles all day is for hamsters.