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MG MGF Technical - Petrol - is there a difference?

Does anyone have any real information on the relative benefits of different brands of petrol? Seeing as this is potentially my main input to the performance and longevity of my car I do sometimes wonder if I could do any better.

Several times I have heard it said that unbranded supermarket petrol is in some way 'inferior'. Can anyone substantiate this and tell me why?

Failing any better information I will continue to use the cheapest (least expensive).

Peter.
Peter

Some of the cheaper fuels do not have the cleansing agents of the more expensive named brands.

Personally I find the car seems to run sweetest on Shell and it certainly did not like the Sainburys' fuel.

And on another point I find in France it likes the Super unleaded and is a little hesitant on French Standard unleaded.

Ted
Ted Newman


When should you/not use the more expensive Super Unleaded?

Does it make any difference?
Does it do any damage?

-matt
M66 MAT
matt

With supermarket petrol stations it is possible to get decent petrol, but you can't guarantee it.

The problem is that many supermarkets are spot buyers. To keep down the price they keep an eye on the market and buy up whatever is cheapest. I assume they do have some standards though. The oil companies have a reputation to think about, so they usually get it right.

Having said that, the only 95RON (normal unleaded)petrol that my F pinks with is BP here in Holland, so I always use 98RON (super unleaded) if I end up in a BP station. This only appears to be a problem in Holland, I hear the BP stuff in the UK is ok.
Tony Smith

In Australia we are told to run the "F" ONLY on 98RON (Normal unleaded is fine for the times you can't find 98RON and really need petrol)

98RON burns cleaner then 95RON (thus the perfomce difference) On the open highway you really can tell the difference.

"F" Engine issues in Australia (from what I hear and can work out) are alot less then the UK...

And the main diffences between these two places are:
~Avg Tempture (AUS 10-35 / UK -10-25) ?
~Petrol (RON98 /RON95 )

Matthew Minion
MJM811 VVC99
Matthew Minion

Of the supermarket petrols, Asda is supplied by BP and Tesco is supplied by ESSO, or at least it was last year, as there was a large article in the Times about petrol prices. It didn't not mention Sainsburys, but i have had no problems with it. It also stated that the petrol supplied to ASDA was the same as that to BP stations.

Regards

JD
John

Matt asked:

>>When should you/not use the more expensive Super Unleaded?

Does it make any difference?
Does it do any damage?<<

A higher octane fuel (97RON vs. 95RON) is more resistant to detonation (also known as pinking). Detonation is bad - at high rpm & load you won't hear it and it will eat holes in pistons in no time at all.

Using a fuel which is more resistant to detonation allows the engine to be configured to use more ignition advance which can yield more power in some places in the rpm band. This configuration is stored in the 'map' in the ECU. Once it's installed it's fixed, the ECU does not know which type of fuel you are using, hence it can't automatically take advantage of the fact that you've decided to stick in some Super Unleaded.

Stock MGF's are mapped for regular unleaded, hence there is no advantage to be gained by using Super. I note that some people report an advantage - I would be interested to know *why* there is an apparent advantage.

Higher octane petrols actually have a slightly lower calorific value (less energy per unit) than lower octane petrols, although not enough to be significant. "High octane" does not mean "high energy", although it's a common misconception.

Using Super will only harm your wallet. It's not a bad idea to use it if you're going to run the engine hard in hot conditions (e.g. on a track) since detonation is more likely to occur under these conditions, hence you're buying a bit of extra protection with Super.

On the subject of petrol brands, many of the big names fill their tankers from the same storage depots - the difference is in the additives which are put in afterwards.

Mike
Mike Bees

I've noticed that the price difference between LRP and unleaded has reduced since the budget.

Is it possible/feasible/wise to use LRP instead of unleaded?

Sorry if this turns out to be a daft question - been a busy week and I cant think straight!!

Paul
P9 VLS
Paul

Many cars nowadays automaticaly adjust depending on the fuel. The F is set fixed for a low octain.

If you have your car "Chipped" this could be another reason to use RON98 (is it 97 in the UK?).

In Germany the have RON92 as well....
Tony Smith

Preety soon i´ll chip my car! The "tunner" has already warned (i already knew) about the restriction of using only 98ron, otherwise it will make auto detonation (pinking) opening holes in pistons: Sounds boring! :o(
Bruno V.

Don't use LRP with a cat.

In fact I don't like LRP anyway if people are reporting differences between the differen main brand unleaded fuels I can say without fear that there is a comparitive gulf (no pun intended) between LRP brands.

The old MG Metro that is back with me as a runabout was always sensitive to fuel variation and the throttle response and performance was markedly affected with different brands. This is still the case and now with LRP it runs like a bag of cr-p. A simple change to BP unleaded showed a marked improvement and smooth idle within 500 metres of the petrol station, this continues.

I have in the past done some different tests on fuel types and effects simply because the effects on the MG Metro (10.5 to 1 compression incidentaly) These started in 1988 when unleaded first came out and wife inadvertanly filled the old EFi with 95RON unleaded. The throttle response was sharper and low speed pick up seemed better. Fuel consumption was worse.

I carried this over to the M16 16 valve twin cam engine when I fitted this in 1990 and noted that there was no difference between leaded and unleaded. Fuel consuption varied by just 1mpg which was too small a difference to be of any significance.

Following the change to the Maestro Turbo in 1992 I repeated the same series of fuel tests using now the three fuel types available. 95 and 98 RON unleaded and 97 RON leaded The differences mimiced the earlier test with the EFi. (same basic O series 8 valve engine) The basically lacklustre off boost response was sharper with unleaded fuels, but the difference in fuel consumption was very significant. 26mpg was the average for leaded, 24.5mpg for super unleaded and 22mpg for unleaded.

Once again when I changed the engine for the T16 Turbo unit I repeated the tests but with just unleaded fuels. (I retained the lambda sensor and didn't want to clog it with lead for the purpose of a 'interest only' test. There was no difference in the respoinse or fuel consumption returns with either fuel.

In all the tests I covered many thousands of miles and the results were clearly down to the fuel types as the consumption changed in line with a change of fuel type.
I also have done some comparitive tests using different brands and found some variations here too.

The clear conclusions I drew from this is that the modern pent chamber twin cam 16 valve design of engine is far less sensitive to fuel type. Other engine designs, especially those with poor inlet tract and combustion chamber desings which do not promote good squish or mixing of air and fuel, are the more sensitive.

In respect of the differences found with different brands now I feel that the engine management control has reached a point of accuracy where a specific rate of burn is anticipated through the combustion chamber from the point of ignition. If achieved at the optimum then the engine performs very well. With other fuels the burn rate and temperatures achieved differ and thus the resulting 'work' transferred to the piston varies which in turn is felt by the driver.

Rog
Roger Parker

I just put an Icon chip in mine today and for the 100+ miles I've done since it seems to run fine on Tesco ordinary unleaded with not even a hint of dodgy detonation sort of noises. The chip was programmed by MotoBuild taking into account the 4 pipe exhaust, Piper Cross air filter and anti-cat that they also supplied and fitted.

As an aside, the above mods definitely make a useful difference to performance (and noise <grin>) and my insurance company only wanted UKP30 extra. :)

Cheers,

Mark.
Mark

From my own experience, many moons ago, as an attendant in a filling station, there is no such thing as Esso petrol or Shell petrol or Tesco petrol. I shall elaborate.

Imagine a fuel tanker delivering to its own forecourt network in a rural area. Once it has emptied it's load it starts the journey home, however, by the time it is ½ way there, the residue of the previous load that was dispersed over the surface area of the inside of the tanker has collected at the bottom of the tank. This residue amounts to quite a considerable quantity - enough to warrant another stop at a filling station. Now the specifics of this example may change, but whilst i was working at my local Q8 filling station, 1 in 5 tankers that delivered was dropping off a relitively small quantity of fuel & came from another fuel company. These residues mix with the Q8 fuel in the underground storage tank - creating a hybrid fuel.

Thus, no tankfull of petrol from this garage was ever 100% Q8 manufactured & i suspect that it is the same elsewhere.

On a slightly different point, i was thinking about the long term build up of crap in the bottom of a car petrol tank the other day & how you shouldn't run the tank dry cos all this crap is then dragged through the engine when i made the association with the underground storage tanks at filling stations. Surely, depending on when the tanks were last filled, the quality of the petrol will vary. Also, these tanks have a far greater capacity & lifespan than the one on your average car/truck/lorry therefore the ammount of crap that must build up in the bottom of these underground tanks must be emmense - cause for worry? Does anyone know how effective a filling station storage tank filtration system is?

If i'm gonna be paying an absolutley extortionate amount for fuel i want to know that i am getting consistantly good quality petrol.

Food for thought...

SF
Scarlet Fever

My experience on two occasions where a fill up led to problems equated to a massive amount of a snad like residue (corrosion grains) which required a tanke removal clean and flush through of the fuel system. The second was one where a quantity of water was drawn in with the fuel which required the same treatment.

The other comment I would make is from living 176 metres from an underground fuel pipeline that travels from a refinery on the East Coast to the Kingsbury oil terminal. This is that where several 'brands' are distributed from a single depot the fuel comes in on a common line. Only when it is loaded into specific tankers will some different additives perhaps be added.

If you take my earlier comments re Esso fuels allowing my engines to run better in my area, it is interesting to note that ESSO have a separate distribution depot some miles from Kingsbury in Erdington (B'ham) and the fuel pipeline (or at least one) comes in from the South West. (I lose the path of the line in Worcestershire) It may be that different results may relate to the different crackers at the different refineries???

Rog
Roger Parker

Well it seems to be clear that there will be no winner in the best generic fuel category, so what about the additives? I guess is in this area then that they are trying to differentiate themselves. Can anyone tell the difference?
Peter Ambrose

Relating somewhat to Andrew / Scarlet's comments:
A few years ago I remember being told that you can't be sure whose petrol you're buying when you drive onto the forecourt particularly in more rural areas. For example, in Western Scotland (I think), all petrol stations get their petrol from a BP refinery, though the lorries that deliver the fuel are branded for the various petrol stations.

I suppose the fuel could have additives such as detergents added according to Esso or whoever's requirements at the refinery?

Any ideas if this sounds correct?

Jim
N125DVX
Alchemy/Austin/BMW/Honda/Rover/MG F 1.8i
(So what's in a brand?)
Jim

What about seasonal factors? Most fuels are changed slightly to cope with different temperatures....
Allegedly.

N837 OGF
Hugh

There are seasonal, or certainly there used to be, to take into account the variations in ambient temps. Winter specs would offer some advantages.

Rog
Roger Parker

Hi all,

My wife took the car to work last sunday and when she got home told me that there wasn't much fuel left.
Got the car out this morning for a run and found that in fact there was no fuel at all!. The guage didn't register a drop. Anyway, i managed to make it to the petrol filling station and they only had 95ron unleaded. That'll do i thought, but on the journey which followed, i found that this fuel is nowhere near as good as super unleaded. The car was still quick but nowhere near as responsive as usual. My next fill will be super unleaded or nothing.

Nick
Nick

This thread was discussed between 23/03/2000 and 02/04/2000

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