View Full Version : Super unleaded - higher octane fuel - I don't understand!

Andy Rylance
6th Mar 2008, 11:31
Ok someone please help!

I drive a ten year old 1.6 engine size car and do long motorway journeys regularly. Would I benefit from any of this super unleaded stuff? I keep reading articles that say "if you drive at a higher rev rating, you may benefit." So say I do about 75mph on the motorway on long journeys is there benefit to this? I don't quite understand what a higher octane rating might do for me.


6th Mar 2008, 11:48
I drive a car that has what is locally called a "Generation Three engine" and 98 octane is recommended but it is not recommended more than about once a month for the straight forward, lower powered engines.
Hope this helps.

6th Mar 2008, 11:53
If you don't experience any pinging, you don't need it. Follow what your manual recommends for your car. Any higher octane than recommended/specified for your car is a waste of money.

The higher the octane, the less likelihood of the fuel/air mixture igniting BEFORE it is intended to (pinging). If you have a high compression engine and it is very hot a low octane gas will ignite from heat/pressure before the spark goes and your engine will ping.

You would probably benefit more with a few doses of injector cleaner when you gas up.

6th Mar 2008, 11:56
Unless it is recommended for your car it is a waste of money.

If it is recommended for your car, your engine will run more efficiently - quicker and more economically. In my experience if you have a car that the book recommends super unleaded, you can get about 10% better MPG,by using it so it just about pays for itself. So if it's recommended you aren't saving money by using the cheap stuff. Your MPG reduces and you lose a bit of power.

6th Mar 2008, 12:08
You might benefit more by trying some Acetone in your fuel.

Add a 100ml bottle to around 10 gallons, but make sure you get Acetone BP (100%) and don't use nail polish remover!

If it works for you, you can get it cheaper from sources other than the chemist.

Andy Rylance
6th Mar 2008, 12:35
Blimey ask a question and get lots of answers in seconds - sod wikipedia you lot are far more useful because I don't get chemical equations to a simple question!

Acetone? ¿Que?

6th Mar 2008, 13:46
Acetone? ¿Que?

Di-methyl Ketone ;)

Might shift some free water (if any) in your tank, but will not add anything to your fuel quality in that concentration.:= If you put enough in, it'll **** up your fuel's lubricity too, would be better to add Isopropyl Alcohol to shift any water.

To anwer your original question, super unleaded will only be of benefit if your car's engine management system is designed to cope with the stuff.

As other have said, check the manual. If thats not clear, do a trial run on super and check your consumption - a simple calculation should then indicate whether its of any financial benefit.

6th Mar 2008, 14:42
There's Mariner9's viewpoint and there's others.

Lots of debate about better mpg and smoother running but I'm not about to add to it. Google it to read lots of discussion but remember those who advocate using it are not making anything out of it if you do,

6th Mar 2008, 16:34
Your car might benefit from higher octane. Most petrol engines give best power where the ignition advance setting is just outside the point where pinking takes place. If the engine management system can recognise a better quality fuel, (knock sensor equipped) it may allow a more advanced ignition setting (my Beemer can tell the difference). This can result in a better performance.

On older cars I have owned (got one now) there can be a marked difference. I manually adjust the ignition advance setting to compensate for quality of fuel used.

Best way is to try it for a couple of tanks full and see what happens.

(Edited to add the word "just", which should have been there in the first place to make more sense)

6th Mar 2008, 16:37
my Beemer can tell the difference

Beemer is a motorcycle made by BMW, Bimmer is a car

6th Mar 2008, 20:04
Beemer is a motorcycle made by BMW, Bimmer is a car

Thanks for that information, I always feel honoured when someone in authority helps out. Any helpful info on fuel grades to go with that superior knowledge, though?

P.S. My mother in law had a car called "Bummer". It wasn't even made in Germany. ;)

PKPF, If you want scientific information ( :ugh:) you really need to put your hand in your wallet, put your own car on a rolling road and get some figures using both normal and super unleaded fuel. Some cars might be better, some might not; even two supposedly identical cars can give quite different results.

Mini fan
6th Mar 2008, 21:52
Shy Torque is pretty much right. Without a knock sensor your engine can't advance the curve to take advantage of the higher octane fuel unless you manually adjust it.

However, if you just stick 98+ in without changing anything you may experience a smoother ride due to the fact the fuel ignites easier. Some say that's just a placebo effect but I definitely notice a difference.

6th Mar 2008, 22:30

Any helpful info on fuel grades to go with that superior knowledge, though?

If you look back you'll see that I did offer useful info, in general terms, as well as suggesting that reading the manual is the most accurate source of the information. I check my Bimmer manual, put together by the same people who designed the car, and go from there.

BTW it is pinging, not "pinking" unless you are thinking of this:


6th Mar 2008, 23:02
BTW - it is 'pinking' in the UK:

verb [I] (US ping)
When a car engine pinks, it makes a high knocking sound because the fuel is not burning correctly.

(from Cambridge Advanced Learner's Dictionary (http://dictionary.cambridge.org/cald/))

6th Mar 2008, 23:12
Beemer is a motorcycle made by BMW, Bimmer is a car
Brilliant, from the pedant, we get ping. Ooh, lovely ping ping.

BTW it is pinging, not "pinking" unless you are thinking of this:

It's pinking ! Arse !

Got this from Wiki:

Knocking (also called detonation or spark knock, pinking in UK English or pinging in US English

There is no such thing as US English. There is English, and there is that Bastard language spoken by twatting Americans !


6th Mar 2008, 23:32
OK Shy, first of all, I apologize for the jab. I honestly didn't know you guys call it "pinking". Just didn't sound right.

Safety, if you are going to quote from Wiki, then either you accept their definition or not. You cannot quote "pinking in UK English or pinging in US English ", then accept the pinking/pinging part but not accept UK English/US English.

7th Mar 2008, 00:33
Pre electronic management systems on engines (MGB and the like) the fuel octane required depended on the compression-ratio and the ignition timing. If your cylinder-head had been shaved (or high-compression pistons fitted) then you needed higher octane fuel and an appropriate ignition timing setting.
When first generation electronic engine management systems were introduced some had a changeover plug to accommodate (usually lower) octane fuels for use when travelling in territories where 'inferior' fuel was standard. Some had settings for higher octane fuels, particularly vehicles that were 'sporty'.
Later generation electronic engine management systems employ sensors to detect 'knock' and adjust engine timing (both ignition and injection) to keep things within certain parameters. You need to know the extent of this compensation (WRT fuel octane ranges). You might be 'lucky' and have settings that will automatically embrace all available fuels, or you might have a system that cannot adjust for super unleaded, in which case you will not harm your engine, merely your pocket.
So, as others have suggested, RTFM . . .
(or contact the manufacturer - being careful to quote the precise model designation from the vehicle identification plate (which might be reproduced in the handbook - but don't rely on it, as the manual might be the wrong one for your model) ).

Using fuel of a lesser octane rating than that which is stipulated by the manufacturer will ultimately harm the engine if you indulge in sustained full throttle use (either under load climbing hills or towing a trailer or high speed travel).

Some engines actually do need higher octane fuel, such as race engines with very high compression and some turbocharged engines, such as the import version of the Nissan Skyline. Also, a few vehicles, such as the new BMW K1200R motorbike, can sense knock and adjust their engine tuning to take advantage of higher grade fuels. Another user commented that the 2004 BMW 330 also does this, according to the driver's handbook it makes 231 BHP on 98 octane and 221 BHP on 95. This ability is apparently widespread amongst German performance cars using Bosch / Siemens electronic engine controls.

7th Mar 2008, 00:38
And again Dush. In the UK we use Beemer to mean a BMW. It's only twattish "R&B" and (c)rap ""stars"" who seem to prefer the other version!

And the octane will make very little difference to where in the cycle the spark plugs are fired, as it's to do with the ability of the fuel/air mixture not to ignite under high pressure/temperature environments, nowt to do with how well it burns or anything like that!

As for any benefits or otherwise of using it in a particular engine, I would suggest consulting the manufacturers handbook, or if you are looking for personal experience then find a website dedicated to the vehicle you drive.

What? You expected some scientific mumbo jumbo from me? I'm just here for the fight!

Right, (rolls up sleeves) Dush, outside, NOW!!!

7th Mar 2008, 01:18
You know, Matt, I haven't been called Dush since high school. It brings back memories. Thanks for that.

This is from Canada, as in NOT USA:

Bimmer vs. Beamer (http://notebook.webaroo.com/external?w=57&webaroourl=http%3A%2F%2Fwww.bmwccbc.org%2Fmisc%2Ftech-and-trivia%2Fbimmer.html&webarootitle=BMW+Car+Club+of+BC+-+bimmer+vs+beemer+perspective)

Enthusiasts vs others
Bimmer - proper accepted slang for BMW cars. Most people don't know this.
Beamer/Beemer - proper accepted slang for BMW motorcycles. You will hear this term used incorrectly by many people.
Bummer - When you get a speeding ticket.
Bitter - Another German car. Very rare; hand built.

So just why is a BMW car called a 'bimmer' not a 'beemer' or 'beamer'?

The answer in part lies in knowing some BMW history and what came first.

All real BMW enthusiasts know that BMW got a big start on two wheels, what many call the real BMWs.

In those days, BMW motorcycles were quite active in racing, and one of their competitors at the track was often the BSA bikes.

Well as things would have it, a track slang developed, and the BMWs were usually referred to as 'beemers' and the BSAs were referred to as 'beesers'.

So, of course for any true enthusiast, there is no way that a BMW car could be called a 'beemer', so they were called 'bimmers'.

Unfortunately, in the US and Canada, and perhaps other countries, there was a time (kind of still is) where for various reasons, a BMW owner was considered an upwardly mobile person, and of course due to the fun in driving their BMWs most all of them had big grins on their faces.

Hence it is little surprise that the non enthusiast types out there incorrectly labeled BMW cars and their owners as 'beamers' or 'beemers'.

7th Mar 2008, 01:24
Dush, what a complete load of unmitigated clap trap!

I am well aware of the history of BMW. Though not a fan personally I can appreciate the engineering.

But trust me on this, in the UK the usual usage is a beemer. Bimmer is only ever heard on rap tracks!

And Canada, that's the USA's poorer little brother isn't it?

7th Mar 2008, 01:34
OK, suit yourself if you like it, use it. I drive a Bimmer.

As for And Canada, that's the USA's poorer little brother isn't it? better not let the folk North of the 49th hear you. The smug Canadians, while at a loss for words to define themselves, are always quick to point out that they are not Americans. They think that they are immune from Al Qaeda when they put the big Canadian flag on their backpacks and travel the world.:sad:

Andy Rylance
7th Mar 2008, 09:04
Bimmer's - well I learn something new everyday.

Maybe I will donate by old car to Top Gear for them to test the fuel theory. But they will end up playing car football with it and bring it back to me in a bag. Probably not. :)

But cheers for the tips all - the old warning "If it works, don't **** with it" is coming to the top of my small brain at the moment. :p

Out Of Trim
7th Mar 2008, 13:00
Dushan - I think the word pinking does sound very like the sound you hear from the noise of pre-ignition. To my ears anyway; I'm not sure were the American use of pinging to describe the sound stems from.

Anyway, In my experience; I do notice a difference in how my VW runs on the the higher octane fuels. It does seem to improve acceleration and increase power output. However, I can't say I've noticed much of an increase in MPG - probably due to me exploiting the extra performance instead!

I do not use it regularly though, with the weekly increase in fuel costs now, It is just too expensive to justify for every day motoring. :{

BP say this about their Ultimate Super-Unleaded fuels:-

BP's Fuel Options

BP Ultimate Unleaded has a research octane level of 97. Standard unleaded petrol has a research octane level of 95. This, on average, gives increased power in certain vehicles.

According to BP, BP Ultimate can give, on average, a 7% improvement in power, a 5% improvement in acceleration and a 6% improvement in fuel economy, in comparison to Unleaded Regular 95 petrol.

In comparison to regular diesel, BP Ultimate Diesel can improve a vehicle's power by up to 10%.

BP have now introduced BP Ultimate 102 unleaded - a precision engineered, high performance fuel to some of their forecourts. This fuel is offered specially for private motor sport enthusiasts and has a high octane number of 102. This means it burns more completely so highly tuned engines perform at their best.

Have to try this 102 stuff sometime - when I'm feeling flush! ;)

only £2.42 a litre :(

7th Mar 2008, 13:13
Well, I've owned BMW cars for nearly ten years now and I think I should be allowed to call mine what I like, in accordance with UK lingospeak, especially as the question came from someone based in London. I had access to one of the first BMW R100RSs in 1977, so I've also ridden their bikes.

I've been building and tuning my own engines since 1971, so I have also read a bit on the subject of fuel grades and compression ratios and I know a bit about pinking/pinging. My little road/trials car engine has a compression ratio of well over 12:1 - it's a topic fairly close to my heart, as it happens.

In my book, pinging is an American term for the noise produced by detonation, in UK it's when you send a request via a computer on a network, demanding a reply from another computer.

Seems to me that some folk with little practical in depth knowledge like to think that saying "read the manual" makes them sound like an expert; but that's in their ears only. :8

Despite what a manufacturer puts in the manual, they only sure way to get the optimum performance from an individual engine is to get it set up properly on a rolling road. A manufacturer will give "safe" advice that will ensure reasonable performance without giving rise to warranty claims.

After all this discussion about differences in "universal" use of the english language, I'm feeling a bit tired, so I'm taking off the whistle and flute and going up the old apples and pears for a Bo Peep. Perhaps some nice American lady would care to knock me up later? ;)

By the way, it's Beesa, not Beeser. First rode those in 1967 and the 1964 250C15 Star I later tuned to hold its own with most 650s of that era is still around, according to the UK DVLA.

Tyre kicker
7th Mar 2008, 14:36
here's a good write up with rolling road run's to see if it really makes a difference.
This is where i take my car to get serviced


7th Mar 2008, 14:53
Well, I've owned BMW cars for nearly ten years now and I think I should be allowed to call mine what I like

I'll see your "nearly ten" and raise you 27 years of driving Bimmers.

As for sounding knowledgeable about reading the manual, you bet I am going to trust the people who designed my $120,000 machine. Besides, there is no harm in using higher octane than prescribed and I said that in my first post. It is just a waste of money. There is, however, harm in using lower as the engine will pin*. It is probably wise to use a bit higher octane these days since they are putting all this enviro crap in the gas (petrol) and who knows what it actually does to the real numbers. It may be theoretically 98, but with ethanol and crapanol in it who knows. Maybe that's why some people are reporting better performance. My problem is usually stepping too hard on the gas and giving the passengers whiplash. In my Mazda Miata it is a bit different, but I have yet to seriously look at timing and tuning it. I use highest octane available in both, which is Sunoco Ultra 94, and before we start another spat, here is a bit about how it is measured here and there, from Wiki:

Measurement methods
The most common type of octane rating worldwide is the Research Octane Number (RON). RON is determined by running the fuel in a test engine with a variable compression ratio under controlled conditions, and comparing these results with those for mixtures of isooctane and n-heptane.

There is another type of octane rating, called Motor Octane Number (MON) or the aviation lean octane rating, which is a better measure of how the fuel behaves when under load. MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, a higher engine speed, and variable ignition timing to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern gasoline will be about 8 to 10 points lower than the RON. Normally fuel specifications require both a minimum RON and a minimum MON.

In most countries (including all of Europe and Australia) the "headline" octane that would be shown on the pump is the RON, but in the United States, Canada and some other countries the headline number is the average of the RON and the MON, sometimes called the Anti-Knock Index (AKI), Road Octane Number (RdON), Pump Octane Number (PON), or (R+M)/2. Because of the 8 to 10 point difference noted above, this means that the octane in the United States will be about 4 to 5 points lower than the same fuel elsewhere: 87 octane fuel, the "regular" gasoline in the US and Canada, would be 91-92 in Europe. However most European pumps deliver 95 (RON) as "regular", equivalent to 90-91 US (R+M)/2, and even deliver 98 (RON) or 100 (RON).

The octane rating may also be a "trade name", with the actual figure being higher than the nominal rating.[citation needed]

It is possible for a fuel to have a RON greater than 100, because isooctane is not the most knock-resistant substance available. Racing fuels, straight ethanol, AvGas and liquified petroleum gas (LPG) typically have octane ratings of 110 or significantly higher - ethanol's RON is 129 (MON 102, AKI 116) reference[1]. Typical "octane booster" additives include tetra-ethyl lead and toluene. Tetra-ethyl lead is easily decomposed to its component radicals, which react with the radicals from the fuel and oxygen that would start the combustion, thereby delaying ignition. This is why leaded gasoline has a higher octane rating than unleaded.

* "k" in UK, "g" in NA.

7th Mar 2008, 14:58
The best way to benefit from super unleaded is to get your turbo engined car remapped. Typically you can expect an extra 30BHP But you really do then need to run super.
For example a remap from Rica has taken my trusty Swedish brick up from 210 to 245, with if anything a slight improvement in MPG (assuming of course normal driving) and a big increase in torque lets you mix it with the low rev TDi boys. If you have a newish turbo - petrol of diesel a remap is great value for money. Very respectable push for very little ankle twitching.

7th Mar 2008, 21:19
There is, however, harm in using lower as the engine will pin*.

It might pink (or it might not), but putting in lower octane fuel wasn't ever suggested, not even in the original question.

Yes, I agree that BMW do an excellent job of setting up their engines; that's one of the reasons I prefer them to others. It's likely there isn't as much to be gained by "playing" with the mapping on the later ones because Beem/Bimm/Bumms did it already. But the thread originator's car isn't made by BMW.

Thanks for taking the time to post the info on octane numbers.

One of my college course projects was based on lab experiments using an ASTM engine; it's a fascinating subject.

7th Mar 2008, 23:38
The use of super unleaded depends on whether the car is designed to run on that RON of fuel. Hence why jap turbo cars in japan make their claimed bhp/torque outputs and run on the 100 RON fuel they were set up for. Same reason why jap imports in the UK need octane boosters or to run on the best brands of super to avoid engine damage and normally produce a slightly lower power output in rolling roads. This also explains why jap cars designed for the US market make far less HP then the Europe/Jap equiv's as they are set up to run on your lowest quality grade of fuel available in the US (which has a pretty low RON level. Think it was around 92 when I was last there?)

That's why model's like the Lancer Evo FQ range and certain other jap cars would never be sold in the US or feature lower spec engines, as they would run far too lean on the fuel available over there.

8th Mar 2008, 00:32
Da do RON Ron?

Lon More
8th Mar 2008, 00:46
I thought Beamers were tv projectors?

Of course in S. London BWWs are rererred to as "Black Man's Wheels" as aout 90% seem to be owned by that section of the poplation. Most of them have also not heard of driving licences or insurance either.:ooh:

In my youth it wasn't high performance unless it used 101. I've still got a drum of octane booster somewhere in the back of the garage from my old Lotus Elan Sll

8th Mar 2008, 05:07
When I had an MGB, using super unleaded (I had a modified head) stopped that annoying pinking.

8th Mar 2008, 19:30
(I had a modified head) stopped that annoying pinking.

Do you mean earplugs? ;)

Andy Rylance
27th Mar 2008, 10:43
Ok after experiments and research I find the following:

Shell UK unleaded is 95 RON, whereas a lot of supermarket unleaded is 90 RON. If there is a supermarket near you then Shell price nearly always matches it.

95 RON gives a much better fuel performance for my old car, and better performance overall.

Shell also told me that their research department also shows that if you constantly fill your car up to full instead of running around with half a tank and letting it go empty and filling it back to a half you are looking at up to a 3% cost in fuel performance due to the excess weight. So that would be 3p in every £1 filled up which over time could bite.

I am now going to look at BP :8

Windy Militant
27th Mar 2008, 16:54
Right can somebody set me right on this then. As a lad I was told that pinking was caused by running the wrong type of plugs, which got too hot igniting the mixture prematurely causing said "pink, pink" noise.
However compressive detonation or dieseling caused by low octane fuel was described as knocking as it made a heavier "tink" or "tunk" kind of noise usually followed by the top of the piston disintegrating.
So which is which :confused:

27th Mar 2008, 17:31
Octane ratings are measured in a test engine by determining the compression ratio at which detonation commences under a given set of operating conditions. They are rather unsatisfactory measurements as they are hard to repeat accurately. That being said, they measure immunity to detonation which is an unsatisfactory end to the combustion process in which the fuel-air mixture ignites at 1 or more points in addition to the one initiated by the spark plug. Detonation is identified on autopsy by destruction of the piston edges. Pre-ignition is identified on autopsy by melting and/or perforation of the piston crown. Motor gasoline composition has changed over the last 20 years or so and is still changing, however back then higher octane gasolines usually had a slightly lower calorific value than low octane. They also burnt slower and were harder to ignite. As an interesting sidelight the very high revving (18-22000 RPM) Honda racing motorcycle engines of the 60s needed low octane fuel as the combustion process would not be complete were high octane fuel to be used.

After an excellent landing you can use the airplane again!

27th Mar 2008, 17:53
"if you constantly fill your car up to full instead of running around with half a tank"

You are also running on less fresh fuel.

27th Mar 2008, 18:46
Good grief! I've no wish to double the number of my visits to filling stations voluntarily. I'm prepared to sacrifice a small saving for the benefit of 600 miles range and two to three weeks between fill-ups.
I suggest driving style has a much greater affect on mpg.

blue monday
27th Mar 2008, 21:09
5TH Gear tested shell Optimax 98 Ron (now superseded by V Power 99 Ron), Supermarket unleaded (95 Ron) and branded unleaded in three cars - Clio, Golf GTI, Impreza WRX STI, it the clio the optimax made no differance in the GTI very little differnce and in the WRX STi there was somwhere around a 14 Bhp increase with Optimax.

27th Mar 2008, 22:14
at a risk of thread drift:eek: I am curious as to what do you drive that gives you 600 miles per tank. Either you have a huge tank or a tiny car, but even tiny cars have even smaller tanks. I thought that most cars are expected to do 300 - 400 miles per tank.

28th Mar 2008, 00:32
Windy, your overheated / glowing sparkplugs cause pre-ignition, not detonation, but pre-ignition might (or might not) lead to detonation. Pre-igniton is when the mixture fires off before the spark occurs.

It's similar when the engine ignition is switched off but the engine keeps running at a low, uneven idle (early Landrovers were prone to this). It can also be caused by a piece of hard, glowing carbon stuck in the combustion chamber. To prevent this, some carburettors had an idle jet cut-off solenoid which is de-activated when the ignition is turned off.

Detonation is when the fuel / air mixture is ignited normally but the gases ahead of the flame front spontaneously explode, rather than burn smoothly. Tetra-ethyl lead formed a dust "buffer" which helped prevent this (but poisoned kids' brains as a side effect).

Either phenomenon causes a pinking noise.

28th Mar 2008, 01:40
Putting higher octane fuel into ur average every day car will probs have little effect on performance unless its mapped to take advantage of this type of fuel. However, I think Shell V-Power for example also has adatives which for example help keep ur fuels system and injectors clean. Its probs worth filling up with it occasionally.

28th Mar 2008, 02:09
Haven't read all posts, but would like to correct at least one misconception re: "pinkging". Many people assume "High Octane gasolines" burn faster than the lower octane and cheaper grade. They may be connecting cost with power, or "volatility" even "Flash Point". "Premium" fuels ignite more slowly than regular grades, allowing high compression ratios and advanced ignition timing to provide more power for a longer period as the piston descends.

28th Mar 2008, 08:14
BP have now introduced BP Ultimate 102 unleaded - a precision engineered, high performance fuel to some of their forecourts. This fuel is offered specially for private motor sport enthusiasts and has a high octane number of 102. This means it burns more completely so highly tuned engines perform at their best.

During the good old days before the phrase "oil crisis" was in common use anywhere, one had a yellow hardtop-convertible Corvette with a V8 327 (or maybe a 350.. time fogs the brain) cubic inch engine. Owning it was a voyage of discovery, having purchased the machine under the press of schedule and not in any way out of love for Corvettes, per se, but only because a Chevrolet dealership was the auto business within nearest walking distance from home on the morning my cranky old Jag sedan ate its transmission while backing out the drive. Bought it off the lot, shiny and slightly used, after a quarter-mile test drive. The whole transaction took about half an hour, IIRC. And an hour after that I was in the air, on a 2-week trip.

One might compare the circumstances to a late-night spontaneous Las Vegas marriage with someone recently unfamiliar. "Interesting", "Sorta
fun", and "Surprising" might have been the descriptors. The earliest discoveries were a) The 'convertible hardtop' was an object the size of a double doorway and rather heavy as well. b) The vehicle would go 90 miles per hour in first gear (of 3). From that same gear it would spin very dramatically by 90-plus degrees if one accelerated moderately from a stop when even a tiny bit of oil or water happened to come under the rear tires.
c) The only fuel that really made the beast happy was Shell 105 octane. All other fuels led to considerable pinking, some signs of detonation (maybe while doing 90 in first) and a strong tendency for the engine to continue running sans electrical ignition for minutes, on pre-ignition and plain stubbornness.

Adding to this a climate with long spans of summer temps over 100F, the options narrowed greatly when Shell stopped making the 105 octane fuel. From that point forward, pinking became as familiar to one's ears as the oboes must be to a symphony conductor. Running in the pink was unavoidable, at times, but one learned to use the pinking noise to tune the cruise options - similar to the 'tune for maximum smoke' approach used in some corners of the radio world. Massively overbuilt GM engine kept on chugging through that all, burning a litre of fuel through the 4-barrel carb for every 2 or three miles at highway speeds.

And the oddest thing was, crazy people, many of them, used to accost one along the road, in parking lots, etc., asking "do you want to sell that car?" If they only had known what a handful it was; but one could not easily dissuade them. That would have been rather like trying to keep teenagers from colliding with their destiny. Reality tends to provide too much information for the tastes of the inwardly motivated!

28th Mar 2008, 08:35
Here is a very informative article, the meat of which was written by John Rowland, who I first met nearly forty years ago, when he used to stop at the end of our road, to oil the exposed valve gear on his Morgan 3 wheeler (with a V twin air cooled engine). John is a real expert when it comes to oils and fuels, I remade our aquaintance not too long back and I was very pleased to hear he still has the same old Morgans!


For many years my grandmother was the accounts secretary at Silkolene Oils, where Stanley Hooker did his research on high octane aviation fuels during WW2. Sadly, the Silkolene oil refinery is no more, houses have recently been built on the historic site.

28th Mar 2008, 09:16
Aah, yes - American tourists.

28th Mar 2008, 09:59
To restore the lead content eliminating "pinking" and poor performance in petroleum spirit just add 250 ml of Aeroshell Fluid 41 or in military terms OM15 hydraulic fluid to a full tank. Might not be environment friendly but certainly works. Great for vehicles like the TR6, Etype, MGC, Alpine/Tiger any vehicle that in previous times used 101 octane fuel. Why worry about buying petrol make your own with blanket wash and OM15 great for petrol generators.:ok::ok:

28th Mar 2008, 11:26
Is Aeroshell Fluid 41 available in the UK ? I have a Lotus Elan Twin Cam 1972 .
On factory tining it likes 105 octane . it now runs with the timing backed off on super unleaded . The head was rebuilt to handle unleaded .
I also have a Subaru WRX which likes Super unleaded . I wouldnt say I get better economy though

Loose rivets
28th Mar 2008, 12:19
Had a mini once that needed 5 star fuel. Would not run on four star. 13.5 : 1 Compression ratio and 50 mpg at 50mph Valve job every 5k.

They don't make cars like that anymore.:8

28th Mar 2008, 13:49

Aeroshell Fluid 41, Esso Invarol FJ13, BP Aero Hydraulic 1F, Brayco Micronic 756 or AMG-10 (Russian) OM-15 (Nato Mil) any of these products work, not sure on availability in the UK. DO NOT USE IN A MODERN CAT NO LEAD VEHICLE) When adding hydraulic oil to petrol the lead content increases up to 500% and the RON value changes. :ok:

28th Mar 2008, 17:14

Are you saying the "Non-zinc anti-wear agent" in Aeroshell 41 is actually a compound of lead, similar to TEL?

28th Mar 2008, 17:35
shy torque

I use a supply of AMG-10 (Russian Mil) and the product contains pb anti-wear compounds, not that I have the facilities to analyse the product. Without a doubt it works. I understand the nearest product to AMG-10 is OM15.

28th Mar 2008, 20:30
Thanks for the info - it might be a useful additive for my "traditional" technology car's engine for an upcoming track event.

Event regulations prohibit me from refuelling from a container in pits or paddock (we must only use fuel dispensed from the pump at the track; I've no guarantee of the quality). It appears that I definitely can't use a gallon of AVGAS in the tank to improve the fuel, as I had originally hoped to do.

I think I'd be allowed to use 250ml of "upper cylinder lubricant" though. :cool:

Say again s l o w l y
28th Mar 2008, 21:29
ON the bike I always used V-Power (99 Octane) as it seems to make a difference, but that is a very high compression engine running at up to 13,500 rpm.

In my BM (not Bimmer, I hate that phrase, Beemer is acceptable) I do notice a small difference with V-Power, but I can't really work out why. My M52 engine
doesn't advance or retard the timing, so how it runs better I simply don't know.

Could it be a more controlled fuel, so there are less "impurities" in it? Does it have different additives in it? Not sure, though I doubt "normal" 95 RON is exactly filthy stuff.

Thorneymotorsports website makes interesting reading.

29th Mar 2008, 00:33
A higher revving engine is less likely to suffer from detonation than a slow one. It's all to do with flame front speeds and high peak cylinder pressure (bad) working against, with high piston speeds working for (good). The high compression is more of a factor, though.

That's why a slow revving aircraft engine is likely to have a problem. Big cylinder sizes, low speed pistons, high torque requirements.

My bike (Honda CB750) and both cars (one an E46 323i) all run better on V-Power. An M52 engine is knock sensor equipped, so on a lower octane fuel it might not run so well; mine does about 5% better mpg on these better fuels, as well as feeling more responsive.

My little fun car engine has really quite high cylinder compression pressures, 225 psi cold, which is probably close to the safe limits for a spark ignition engine. It relies only on the thickness of the head gasket (1.25 mm)to prevent the pistons hitting the cylinder head. I'm presently looking for a thicker head gasket for it!