Guzzle puzzle

ON THE face of it, you should be getting about 5 per cent better fuel consumption with the Optimax. That is provided everything else is the same. The higher density of the Optimax means you are putting greater energy into the engine, and that should mean you are getting greater energy out. You should be able to drive with a lighter throttle for the same performance. I would suggest you recheck the engine tune, and perhaps go back to regular unleaded for a tank or two before trying the Optimax again.