MPG

[Major Rant]

trying desperately to remember why a higher petrol RON rating for a motorbike was a waste of time and the relationship to engine knock,,,,

    Its because the sportsbike engine is designed to run with a 12:1 compression ratio and if you try and run it with a "stochiometric mix" (ie just enough fuel so that ALL the oxygen gets consumed) then the 'ignition temperature' is below the 'compression temperature' and the charge will ignite before the spark happens and your engine will run badly and eventually destroy itself.  Adding fuel to the mix makes the charge more reluctant to ignite - hence the spark happens first and the charge goes 'bang' at the right time but the extra fuel gets thrown away down the exhaust pipe. (Which is why a Honda 90 does 120MPG but a Fazer does 45MPG)  Some car engines (maybe 'most' by now) have knock-detectors that adjust the mix and frig about with the ignition-timing depending on what grade of gasoline you are using.  (all of the above is based on 10yr old knowledge when bikes had carbs, cheap cars had crude ECUs and posh cars had proper engine management systems. Its probably changed by now .) (By the way ... The new Ford 3 cylinder 1 litre engine is a wonder to behold ... check it out!  http://www.ford.co.uk/FordFleet/NewsAndR...ost-Engine)