Hi guys when running high octane fuels like e85 or 98ron will u get less km,s out of a tank than e10 and could it be explained why.

Should be much the same really.

In my head I always think that i'd get further from higher octane fuel as the engine has more available energy to burn and therefore wouldn't have to work as hard to move the vehicle. But in reality the carburettor/injectors are still supplying the same volume of fuel regardless of octane.

I'm sure google would have an answer for you.

octane is the index to resist knock. alcohol fuel and gasoline have different air to fuel ratio need. you need more fuel if using alcohol to get same output as gasoline fuel.

gasoline stoich AFR is 14.7:1 while E10 AFR is around 14.12:1. that means, for gasoline, you need 14.7 part of air to burn 1 part of fuel. but you need 14.12 part of air to burn 1 part of e10. that means, for the same amount of air, more e10 needed than gasoline.

yeah but Stoichiometric ratio is only one element to fuel economy.
Smart ECU will lean the engine out during cruise, which will increase fuel economy. What this does is increase the engine running temperature, which in turn promotes knock.
So theoretically a higher Octane fuel with has a lower Stoichiometric ratio (and coincidently lower relative energy output such as ethanol compared to petrol) can produce better economy figures because the engine can run leaner and hotter without pre-ignition.

Not saying that is a given, just it is possible given the right circumstances and equipment.

you can only run so lean until misfire or have to open up the throttle more because of power loss just to move the car.

i'd be interested to see which fuel can actually produce more MPG.

Premium street petrol is proven to get better fuel economy than E10. All it takes to get better economy is a slight timing adjustment, which you can do with any old distributor. E85 will require even more fuel for the same power output, and requires rejetting the carburetor.

Now if you are supercharging or turbocharging, then E85 has some advantages over RON98, so the story is totally different.

If you want power throw economy out the window.90l of e85 would barely see me 280km

The calorific value of the fuels are different that's why you use more e85 v 98 even though it is has a higher octane,
Exactly what Datrotor said ^^^^^^^!