Who is kidding who here. Petrol nearly invariably comes from the nearest refinery and it doesn't matter whose name is on the pump. Does anyone seriously think that Shell sends petrol from the Midlands to Grangemouth when there is a BP refinery on the doorstep?
Yes, they may put some additives in the tank and you may remember a few years ago when a much advertised additive by Shell had to be withdrawn because it was damaging engines,mainly Vauxhalls.
As for the nonsense that a modern engine ticks over at 600rpm on one petrol and 750rpm on another, it is just that nonsense! The tick over speed is determined by the ECU, running even on ONE cylinder an engine will tick over at the normal rpm if somewhat eratically.
One motor magazine did some tests on various fuels recently. It essentially showed variations in performance, sometimes with the SAME fuel on different days and some variation with particular engines. Indeed an engine with a compression ratio that does not require a high octane fuel will generally deliver a higher mpg on the cheaper fuel. Why? because higher octane fuels have generally more fractions of more volatile constituents which also tend to have a lower calorific value(CV). Lower CV means less heat and more fuel to do the same work. When did you last see a company advertising its fuel with a high CV. I guess never and I can guess why!
One conclusion of the tests was that it was worth getting fuel from a busy forecourt be it supermaket or garage, to get fresh clean fuel.
My car has 176k miles with supermarket fuel in the UK, France and Switzerland. Still on original injectors and fuel pump, head never removed, oil and filter every 6k and fuel consumption as it was at 10k miles.
Last edited by Ramian; 04-02-06 at 09:36.