Over the last couple of months i have been conducting an experiment ito whether it was worthwhile for me to use 99 RON petrol and whether it would get me any better MPG like people claim it does.

So for just over 1700 miles of my commute which consists of A and B roads and i'm probably averageing a 40mph average speed but anything upto 80+mph on the B roads, i had these results:

Tank 1:
99 RON
46.21 Litres
329 Miles
32.37 MPG

Tank 2:
99 RON
44.80 Litres
329 Miles
33.39 MPG

Tank 3:
99 RON
48.43 Litres
339 Miles
31.82 MPG

Tank 4:
99 RON
48.43 Litres
350 Miles
32.87 MPG

Tank 5:
99 RON
53.00 Litres
387.5 Miles
33.24 MPG

Tank 6:
95 RON
47.03 Litres
352 Miles
34.03 MPG

Tank 7:
95 RON
46.91 Litres
353 Miles
34.21 MPG

Tank 8:
95 RON
44.41 Litres
331 Miles
33.88 MPG

Tank 9:
95 RON
44.50 Litres
330 Miles
33.71 MPG

Tank 10:
95 RON
44.80 Litres
329 Miles
33.39 MPG

So hopefully this should now answer peoples questions as to whether 99 RON petrol improves the MPG on a standard coop.

It does not improve your MPG at all.

Obviously if you are using a car which has been mapped for 99 RON fuel your results will be different. But for a completely standard 20vt you wont notice any difference other than a slightly lighter wallet.

That's good to know. Did you notice any difference in performance between 95 and 99?

I can honestly say that i didnt.

Then it's clear that the standard setup doesnt adapt itself in any way to take advantage of the higher quality fuel. On modified cars it's a different story though.

This is a bit irrelevant, but I also had no joy with Tesco 99 in my Alfa, but I'm finding the 97 RON from Sainsbury's does make a difference that easily justifies the extra 3p it costs per litre. I'm getting about 10% better economy with it.

I have it in the Coupe as well but the short trips I make and a tendency to get carried away with the right foot mean that I'll never have a set of meaningful figures.

Can you now test this with Shell?

I would like to see the definitive answer on Shell V Power!!!...............the amount of times this V power subject has reared its head on the many forums i have been on over the years, I have lost count!

I have used it in many E36 M3's....can't say it ever felt any different..

..placebo effect with added benefits to the Shell oil company....no doubt many will differ !

Do a search for Begbies post that has engines broken down and shows how much cleaner the engine is on the higher ron, as its not just the ron, but also the cleaning additives that are added... and for me its worth it for that alone..

Also, and not saying that your test isn't correct Truff, but the likes of BP, Shell, etc would not get away with "adds 15% to your MPG" or whatever their claim without having proof to back it up, or they would have to end it in "probably"

I thought Optimax made quite a difference to the performance but that was 10 years ago.

V-Power didn't seem to make much if any difference to economy when I filled up with a tank of it recently.

Tesco 99 actually performs worse than 95 in my scooby! It costs me about 30 miles per tankfull of the expensive stuff over the same 180 mile commute.....in the Fiat (20v Vis) it seems to make no difference at all!

Jon, try the trusty old ECU reset in the Scoob then you'll notice the difference big time

Bog Standard 95 RON for me every time - no complaints.

This is really all about the clean engine effect than better mpg. Running a higher ron does indeed keep your engine much cleaner & if its tuned properly, does give that little more ump, in some cases.

Maybe you could try the same in the Coupe, allow it to re-learn?

same format as the Coupe reset wal?? touch neg and pos??

I tried the test with the ECU reset (several times) after recent problems with my coupe...still didn't make a difference

Same here

95 RON fuel for me too.

And me. Wouldn't touch the supermarkets own petrol wtih a bargepole though. Shell or texaco for me - has the proper detergents in there. Every week almost in Honest John's section in the telegraph motoring mag there's an instance of a reader changing from Supermarket fuel to Shell/Texaco and their problem vanishes. found some info here

Same "Downunder". Have experienced it with our old Croma that was the wife's daily drive (now a Grande Punto) and a number of reports from some mechanics that I know.

The same applies to supermarket "home brand" oil, have heard reports were this has not done its job properly resulting in excessive wear.

The same old story, "you get what you pay for".

I always use Tesco 99 as its the closest petrol to me, Shell is about 10 miles away.

But... just been reading a few things about people having cold start issues it.
At the moment I have cold start issues (a few months now) always starts but often not very happy about it.

Going to try changing to BP ultimate to see if there is any difference.

Does it make much difference when the car is mapped as to which grade of petrol you have in the tank ?
I remeber Leighton asking me what I was using ,RON 95 OR 99.

I think it does matter which octane the car was mapped on. I use Vpower but when i fill up with 95, there is quite a noticeable difference! It'll just lack power somewhat..

Doh! and there was me thinking this thread would put an end to the 'Which fuel should i use' discussion.

As for Shell, there is a garage reasonably near me and there is also a BP up the road but i have no plans to continue my study with these fuels...

unless you care to cover the cost

Fuel octane is very important, ESPECIALLY if your car has be mapped accordingly.

The difference between 95 & 97 octane is significant, the difference between 95 & 99 octane is frankly night & day. The more power you have, the greater the requirement to use a high octane fuel regardless. For standard cars, 95 octane is fine for all occasions. However, if the car has been mapped then it must use the correct fuel for which it was tuned. For this reason I always ask what fuel is in the tank, and also advise that this fuel always be used, unless in emergency. By this I mean fill up with £5-10 of 95 if you are running on fumes, but do not go on boost or thrash the car around until you can fill up with the correct fuel. What happens if you don't, well the car will invariably start to detonate, which leads the ECU to retard the timing loosing power quickly.

The 20vt ECU is adaptive in that it can detect knock (or even the onset of knock) very accurately. The result is retarded timing to protect the engine, but there is a limit. It cannot, however, advance the timing to take advantage of high octane fuel, there is zero performance benefit unless the car has been mapped. If your car has been mapped for 99 octane and you then use 95 octane, as soon as you go on boost the engine will start to knock, unequivocally.

Recently I have noticed a small trend that the fuel requirements are perhaps not passed onto the new owners when cars are changing hands. This is very important information and I would advise listing it in any 'for sale' advert.

In terms of mpg, if all things stay equal i.e. tyres, drag, mechanics etc, then maximum economy can be achieved with the following for petrol engines:

1. Introduce a lean burn i.e. lean of stoich, when cruising.
2. Increase torque so gearing (rpm) is maximised.

Option two is the most common way of increasing mpg, it is for this reason why diesels are so frugal, and the way to make them more frugal is to increase torque significantly by injecting more fuel.

More torque = less frequent gear changes, less throttle and reduced rpms = increase MPG

In a remapped 911 turbo you REALLY notice the difference even between 97 and 99 RON. BP or Shell for me every time to liberate all the horses and keep things clean. Annoying thing is that the nearest Shell garage to Chelmsford is 13 miles away in Rayleigh and the local BP garages only sell the 97 version of Ultimate. My area sucks for decent fuel.

That will work (certainly on the classic shape) but there is another (quicker)way to do it under the drivers footwell using a shorting strap. Problem is Jon I can't remember where now as it's been a few years, have a look on Scoobynet and I'm sure it will be there.
Make sure you run the 95 in your tank down to nothing and top up with rocket juice before resetting, then enjoy the serious increase in power/torque. It really is noticeable and almost worth the extra cost.

Tried my vis as well with no joy

Flea, you mapped my Coupe on 95RON. I take it that it's perfectly safe to run on V-Power? I take it that running a car on a lower octane than it was mapped to is what's dangerous.

Yeah you can stick higher octane in if it was mapped on 95, just not the otherway round.

My car still has the BMW sticker in the corner of the clocks stating that it needs 98RON or higher. When there was a V-Power shortage I was caught short and had to run a tank of normal Shell 95. The difference was night and day, not necessarily in performance, but in how sweet it ran, idled and picked up.

V-Power every time for me.