[ukmicky (OP)]

I usually put high octane fuel in my car as it runs better. However a litre of high octane unleaded petrol costs more which increases the petrol cost per litre.

But as high octane has more punch per litre does that mean i can travel further on a litre of high octane reducing the cost per mile effectively making it as cost effective as low octane.
Confused  [] i hope so []

_{Mod edit - Formatted the subject as a question - please do this to help keep the forum tidy and easy to navigate - thanks!}

[turnipsock]

Yes.

I've been using Optimax and Ultimate for a while and wouldn't use anything else now. I often wonder what people think when they see me filling up, but a glance at the milage might make them think, 182,000 miles.

I used to work at the refinery at Grangemouth in the IT dept and had the chance to speak to the guy in the tanker terminal and he told me all about the process. Even though all the various fuel companies fill their tankers at the same refinery, each company has it's own gantry and they each have different additives and tweaks. Tesco and Asda don't add anything to the fuel and it will wreck an engine pretty quickly.

The good fuels have various additives that make your engine run cleaner.

As Micky says, the car will run better.

[lightarrow]

I usually put high octane fuel in my car as it runs better. However a litre of high octane unleaded petrol costs more which increases the petrol cost per litre.

But as high octane has more punch per litre does that mean i can travel further on a litre of high octane reducing the cost per mile effectively making it as cost effective as low octane.
Confused  [] i hope so []

You should measure how many miles your car does with 100£ of high octane fuel and with 100£ of normal fuel, then you will choose the fuel with higher mileage...

[turnipsock]

The problem with putting in one fuel then the other is that you know what fuel is in the car so you can drive in a different manner and affect the results.

You could get somebody else to fill up the car for you, and not tell you which fuel is in the tank, but you can feel the difference and then drive more econamicaly (sp?)

http://uk.youtube.com/watch?v=cxghVlSGwEQ

This would be a good test if it was not for the Ultimate car slipstreaming for a long way.

[Pumblechook]

I think I read or heard it on telly that high octane is a waste of time for ordinary engines. 

US and European Octane numbers are worked out differently.   

[lyner]

High octane delays the combustion and allows higher compression ratios. If you use higher octane fuel than your engine is designed for then there is a danger (in extreme cases) of burning exhaust valves if significant combustion is still happening as the gases exit the cylinder.
With modern engine management systems, this may not be a problem.

[Pumblechook]

Some do claim that high octane fuel improves their MPG but some claim that putting a magnet on the fule line also improves MPG which is nonsense. 

There are websites full of schemes to boost MPG and tests have shown that most don't work at all.  Some show a slight improvement. Many show a worse MPG.  Some can damage the engine.  Some are dangerous. 

The advice on motoring sites is to alter your driving style to save on fuel. 

[graham.d]

The engines in some cars can adapt to different octane ratings. A BMW530i runs better on higher octane fuel and gives an increase in fuel consumption about in line with the difference in the fuel price. The same goes for Mercedes S280 and I expect that this is true of many modern cars.

[lyner]

The oxygen sensor in the exhaust will help the engine management computer make sure that as much of the fuel as possible is burned. That's a good way of optimising efficiency. In the days of carburetors that wasn't possible.

Pumblechook is right when he says that driving style makes more difference than most things. Drop your top speed to something nearer legal for a start. It has very little effect on average speed on many journeys. And avoid rushing up someone's backside and then braking hard.

I think graham.d means "reduction in fuel consumption" , I think?

[Don_1]

I try to stick to around 55 - 60mph on motorways, that does give me better milage. Also it pays to go up through the gears fast, with gentle acceleration.

Many times I have pulled away from lights and am in 3rd or 4th gear when a twit passes me in 2nd with the engine screaming. A few seconds later their brake lights come on as they brake heavily at the next set of lights, then off again like a bat out of hell, engine screaming and tyres screeching.

[lyner]

Yeah. We're old farts but we save money!

[wannabe]

Octane number reflects burning characteristics (flame point, flame front travel etc.) related to compression ratio. The manufacturer will specify the most efficient octane number and using that will result in the optimum gas mileage.
Price will determine cost per mile and lower cost gas, even at the penalty of slightly worse gas mileage, often is more economical to use.
Gas lower in octane then the compression ratio requires will result in "knock", noticeable as a pinging noise, as if some loose nails were rattling about inside the engine, usually not very loud but audible if one listens carefully and becoming louder under increasing load (as in going uphill or under acceleration). This is caused by changes in the burning characteristics of the flame front spreading from the ignition point at the spark plug and actually is a series of minor explosions rather then a smooth burn! And that is what can cause damage such as pinhole burn through of the piston.
Lesson: use the lowest octane gas NOT causing "knock" or "ping"