Bin Man:
Q&A: How Does Ethanol Affect Fuel Economy
Very simplistic explanation.
Cylinder pressures play a larger part in the efficiency equation than energy density of the fuel and you can’t run efficient cylinder pressures on 95 octane fuel let alone 87 octane.
It’s the octane rating of E10 which is the bigger problem let alone the type of 87 octane muck that he’s referring to.
The ignition timing has to be backed off to the point where it cancels out any cylinder pressure advantages.If drivers then try to use a lot more throttle to compensate for the resulting lost acceleration throughout the range that could easily create 2 or 3 x worse mpg figures in the real world.
My Zafira isn’t even a turbo engine but it suffers very noticeable pinking on regular unleaded and that was even before E10 was introduced.I long ago swapped it to V Power etc.
The government are obviously deliberately setting it up to fail when 5% more ethanol somehow results in at least 4 points off the octane rating over E5 super unleaded.When the 10% should be added to the 99 octane super unleaded base fuel used for E5 thereby raising it to over 100 octane.