New Petrol from Shell, claims to increase MPG!

[Beer Jammer]

Over here in the UK, Shell are running an ad that claims they are replacing the usual unleaded petrol for their new Fuelsave Unleaded that can allow you to save the equivelant of 1 litre of fuel per tank full. So, the average UK fuel tank is 60 litres, this is an increase in economy of 1.6% in very rough calculations.
More info: Shell Fuelsave

Now, I know a reasonable amount on internal combustion, and the way I see it is that this fuel improves the smooth running of your engine by using an additive, allowing the engine to produce less friction. This means it takes slightly less energy to turn the wheels, hence less throttle needed and a saving of fuel. So you will see a saving if your driving style stays the same and you dont go around full throttle most of the time

Right, so that should mean that you get more power to the wheels at full throttle with the new fuel than before. That surely must be a great news to all If the MPG saving is 1.6%, that should mean 1.6% power increase. Not great, but as the new fuel is the same price, and you need it anyway, thats a free 1.6% increase.