Common Question this one. And there is a wide variety of opinions on it. Any way, legislation has demanded that the oil companies take the lead out of petrol because the heavy metal pollutants it causes in exhaust fumes MAY increase the risk of poor mental development in one in a thousand children. Instead, the authorities insist we use 'unleaded' fuels, which to compensate for a lack of lead, use an increased concentration of Benzene derivatives, which are carcinogenic to every-one. Hence the big rubber rings around the filler nozzles at the petrol stations! Is it my imagination or is there something wrong in the logic there?
Any way, that's the story, and we are stuck with it. So before talking about what you can do about it, lets have a quick look at what the lead was in petrol for in the first place.
Now, you have all heard of 'Two Star' and 'Four Star' petrol that we had before unleaded, and now we have 95RON 'Regular', and 97RON 'Premium', but apart from the lead, what is the difference?
OK, well, RON stands for Rated Octane Number, and is a measure of a thing called 'knock resistance'. Still pretty meaningless, I know, but bear with me.
Knock, is the phenomena of pre-ignition, and occurs when the charge self ignites through heat and compression in the engine, without the spark plugs lighting it. Diesel engines actually depend on it, because they don't have spark plugs, and it is why they sound like there's about a thousand dwarves inside the engine block with sledge hammers, all trying to get out - but in a petrol engine, it isn't healthy.
Knock, Pre-Ignition, Detonation, by whatever name you know it is a very bad thing indeed. What happens is that the charge in the cylinder explodes early, rather than burning when it should. So the first thing that it does is try and push the piston back down the cylinder before its passed top dead centre, so it tries to turn the crankshaft backwards. The next thing it does is get things rather very hot. Hot enough to melt things. Usually exhaust valves and piston crowns.
Now when a manufacturer develops and engine, they spend a lot of time worrying about the compression ratio, and the carburetion, or mixture strength, and the ignition timing, so as to avoid detonation and get the most power and economy they can from an engine.
The actual fuel they will optimise the engine for will be either 'two star' or 'four star'. Two star petrol is the old fashioned leaded equivalent to 'regular' unleaded, with an octane rating around 95. Four star petrol is the old leaded equivalent of 'premium' unleaded, with an octane rating of 97. Well, that's not strictly true. 'Proper' four star had an octane rating between 97 and 100. So 'Premium' is only just on the lower limit for comparing to four star, but it's close enough for most.
If you are interested the 'octane rating' is a percentage derived from some pretty high powered maths and things called 'dimensionless groups - but I wont get into that. But the way it works is that they test a sample of a control fuel, off the top of my head, its 'Iso-' something or other - I cant remember - Iso-Benzate, maybe? Any way, the control fuel has a fixed calorific value and knock resistance, so they assign it a 100RON index. Everything else is compared to it, and those that do better get higher octane ratings, and those that don't do as well get lower ones.
Now, it's a bit of historical legacy, and the old 'ministry of supply' but there used to be a big gap in both price and availability of higher octane fuels. And back in the 1960's you could actually buy 'one star' petrol that attracted almost no duty for use in things like generators and lawn mowers. But obviously, these didn't exactly have high performance engines. Rated by power rather than capacity, they could use a slightly bigger engine and a low compression ratio in order that they could make the required power on lower grade, cheaper fuel.
Cars, on the other hand, needed something with a little more pep, and most manufacturers standardised on two star petrol. It carried a slightly higher rate of duty, but was good enough to allow a reasonable compression ratio and so a reasonable power from a typical sized engine. And that is still true today, with most manufacturers designing cars to use unleaded 'regular' fuel.
For higher performance engines, to get more power out of the same engine size, you need to get a bigger bang, which means a higher cylinder pressure, so more likely hood of 'knock', so you need a higher octane fuel. Consequently, most big saloon cars and sports cars, where economy wasn't so much an issue, were often optimised to run on the more expensive four star.
Any way, the point is that the higher octane rating allows a higher compression ratio and or a higher state of tune, so more power.
Before I go on, I'd just like to point out that it is a common misconception that higher octane fuel is more 'powerful'. Actually, the calorific value, or the amount of energy contained within a sample volume of two star isn't much different to that of a similar sample of four star. Using four star or 'premium' over two star or 'regular' in the same engine won't make one jot of difference to the power the engine makes.
To illustrate the point, in the 'olden days' racing engines were often tuned to run on methanol, which allowed a much higher compression ratio, often in the order of 15:1, where normal production engines would often be using little more than perhaps 8:1. This helped them make a lot more power, but, while methanol has an octane rating well over 100, maybe about 108RON, it actually has a much lower calorific value. The extra power came not from the octane rating, but from the extra cylinder pressure generated by the high compression ratio.
On the other hand, nitrobenzene is often used in 'top fuel' dragsters. This fuel actually has a very low knock resistance. Incredibly low in fact, but then the stuff is technically an explosive not a fuel. Give it a bit too much heat or compression and it will do untold damage, but it has a very high calorific value, and can make a little engine make a lot of power - provided nothing goes bang first!
So, back to the plot; Lead. The lead, as I've said essentially increases the fuel's knock resistance and raises its octane rating, which is good, because it allows for a higher state of tune and there fore more efficient engines. But, it also has some other effects, and they are mainly to do with lubrication.
Inside the combustion chamber, you do have moving parts. The piston and the piston sealing rings can get a bit of lubrication from underneath, where oil is sprayed around near the crank-shaft. Above the cylinder, where the valve springs and rockers and everything are, again, oil can be pumped up and allowed to splash around keeping everything well lubricated.
Which leaves the valve stems and the valve heads to be lubricated. The valve stem, rattling up and down in the guide at whatever speed, isn't going to last very long unless it has something to reduce the friction. Likewise, the valve head isn't going to last very long hammering into the valve seat every revolution.
But if you let any oil get down there to keep them wet, well - its going to be burned off pretty quickly as soon as you ignite the petrol and air in the cylinder isn't it?
Lead is a help here. It can withstand the heat, and wont burn off like oil will. It gets in through the petrol and sort of condenses out in small particles like dew on the valve stem and seal, and builds up a protective layer of lubricant. With each cycle a little is worn away, and a little more added, but overall you tend to develop a pretty even layer of lead that replenishes itself with use.
Or at least until you have to switch to unleaded fuel.
Now, at least the octane rating hasn't been changed, so we shouldn't have to worry too much about 'knock', other than perhaps to adjust the ignition timing a bit.
But, what is a worry, is that the new petrol will start to wash the lead from the valve stem and seat, removing its lubrication. Ultimately this will lead to worn or pitted valve seats, which ironically can cause detonation, or excessive wear in the valve guides leading to high oil consumption and emissions.
So, what can be done?
Well, the first thing is to put the lead back in the petrol. Note that I said that the lead lubricant is gradually eroded over time. This is called the 'lead memory effect' and can last a long time before all the lead is washed away and accelerated wear occurs.
Until recently, while leaded two star was being phased out, it was quite common to recommend people merely to have the ignition adjusted so that the engine would run on unleaded OK, then to just use one tank of leaded fuel for every two or three of unleaded. This meant that the engine still saw some lead getting deposited, from time to time, so that it shouldn't wear away, or at least not so quickly.
This is now almost impractical, given that almost no petrol stations are stocking leaded two star or lead replacement fuels. Which means that the next solution would be to use a 'booster' or 'leaded fuel additive'
I shall quickly mention these are proprietary bottles of concentrated chemicals that are added to the fuel tank each time you fill up and are burned with the fuel. Some are merely lead substitutes and used as directed to treat regular unleaded, will give you an acceptable substitute for old fashioned two-star petrol.
Worth mentioning here, is that the 'lead' that was in old leaded fuel wasn't in the metallic form, it was held in suspension in an ionic form or loose compound that would easily release the lead in the metallic form. Most leas 'substitutes', are similar, they probably don't actually contain any lead or lead compounds, as the same legislation that prevents them being used in pump fuel will prevent them being added retrospectively.
Instead, the preparations will contain other compounds that will provide the same lubricating properties as lead. Each preparation will be different, and I haven't looked at any to check, but I would imagine that they are derivatives of 'synthetic', that is sort of genetically engineered lubricating oils. They will have long strand carbon molecules with probably ferrite or iron or other metals in them, that will be attracted to the metal of the valve stem & seat pretty much like the lead would have been.
Any way, if you have an old Land Rover, this is probably all you need. But, I'd strongly suggest that you read the label on the bottle carefully, and or contact the manufacturers, because in an old Landy, chances are you may be able to get away with a lower dosage than a lot of other 'classic' cars, by virtue of the fact that they were designed to run on poor quality fuel to start with.
Other additives are 'octane boosters', which may or may not have any lead substitute in them, but are intended primarily to increase the octane rating of the fuel.
These have been around for some years, and used to be popular in racing circles where regulations had allowed the use of high octane 'five star' fuels, and then when the standards were revised, and the octane rating for 'pump' four start was dropped from the level that motor-sport governing bodies said were permissible.
Now, looking at my books, I think that most of Solihull's finest are intended to run on two star, so there shouldn't be much need to use an octane booster lead additive. BUT, I did notice that some of the V8's with higher compression ratios are intended to run on 97RON fuel. If you have a V8, then you have a choice, use 97RON unleaded with a lead additive, or a boosted additive on 95RON unleaded. But you might be able to get away with 95RON unleaded and an un-boosted lead additive.
The best advice I can give is to take advice from the people selling the stuff and if necessary the preparation makers - they should have data sheets that can help you work out which is the best one for you, and what dosage to apply it in. Failing that, you could spend some time mixing up fuel samples, dosing a gallon of petrol at a time with different ratios of preparation, and trying them out.
I've often done this on two stroke motorbikes to find the best pre-mix strength for the oil in the petrol, either when I've rebuilt, an engine, tuned one, or decided to try a new brand of two stroke oil. Its a bit of a pain, because you have to try and optimise the fuel mixture and ignition each time you try a new sample, then gauge whether what you have done has made things better or not, but it has always proved worthwhile.
It may seem a bit of an un-necessary palaver to go to for a road car, and you would THINK that the preparation manufacturer would have done all that kind of thing before they put the stuff on the market. However, it is actually very unlikely that they will have tested every single car and engine and found the ideal dosing ratio for every type of vehicle. More than likely, they will have tested the stuff on a number of common engines to find the ball-park dosing ratio, then tried that across a slightly wider selection of engines to make sure that there is no obvious adverse effects, then chosen a dosing level that gives a good margin for error.
So doing the tests yourself, for your specific vehicle, may be worthwhile to get it right for you, if you intend to use it as a long term solution.
Now onto the warning. There are a lot of adverts out there for what I shall call fuel 'widgets'. (See:- Wonder Fuel & Widgets! ) Sometimes these are described as catalysts or ionisers or magnetic fuel polarises. But there are essentially three types of 'widget'.
- The first is the 'in-line' widget, described as being just like a fuel filter, the petrol flowing through it and being mystically transformed on its passage from one end to the other.
- The second is the 'external' widget, which is described as fitting around the fuel line and again, mystically transforming the fuel as it passes by.
- The last, is the 'drop in' widget, that is described as dropping into your fuel tank, and doing gawd knows what, mystically to your fuel.
Have you got the impression that I am a bit cynical of these devices yet? Well, just in case you hadn't picked up on it, I think that these things are about as likely to do anything useful, as a Liberal Government.
Now a lot of claims are made for these widgets, from boosting power, to improving economy, to reducing engine wear, making the engine more responsive, to, err, well anything that you could want from your cars engine, to be honest. But, in recent years the most vaunted claim has been to either replace the lead in the petrol or eliminate the need for it.
And the advertising blurb is convincing, I'll give them credit for that. There are usually a couple of ploys. The first is the 'Secret Formula' ploy. This plays on the idea, and a bit of urban legend that some mad inventor working for the government came up with this wonderful idea, but because it was so brilliant the technology was suppressed, either by the government, because it would have destabilised world power, or by the oil or car companies, because it would have destroyed their businesses.
And the 'So brilliant it was suppressed' idea has been with us for many years. Sometimes it was a fuel, sometimes a carburettor, sometimes a whole engine. And to be honest, there are probably some seeds of truth in the legends. Nitrous-oxide was originally developed for the military during world war 2, and was classified right up until the 1960's, by which time enough ex-RAF or USAF mechanics had hopped up their racing cars with a little laughing gas from the dentists. And fuel injection and turbo-charging and things have also seen much secret development work. As have many many alternative engine designs.
But, while I normally go along with a lot of 'conspiracy theories', and look for the power play and hidden motives behind the official facade, on things like the Kennedy Assassination and the Gulf War, I have studied to much physics, too much chemistry and too much automotive engineering, to be convinced by these stories.
I am also cynical enough to believe that while there are enough incredibly clever and influential people out there to make conspiracies possible, I've also met far too many stupid, ignorant, and gullible people to make me believe that a lot of them aren't just every day ef-ups, mis-understandings or pure fantacies.
Any way, the second main ploy the 'widget' merchants use is the 'scientific logic' technique. They put together something that sounds wholly plausible, using scientific language deliberately chosen to use terms that you have probably heard, but probably don't actually understand completely, to suggest that what they are offering you has some sound scientific technical basis. They will often also back it up with extracts of scientific or authoritative reports, but rarely hard facts.
And as often as not, they will combine the two ploys, and wrap it up with some good old fashioned marketing technique such as customer testimonials, money back guarantees, and 'special offers'
Basic fundamental physics will tell you that the energy released by a chemical reaction, like combustion is all down to the potential energies between the chemicals at the start of the reaction and the chemicals at the end of the reaction, and the calorific value, or the amount of energy that can be released is wholly dependent on what you have to start with, what you have at the end, and the energy released is the difference twixt the two.
So fundamentally, no 'filter' or 'catalyst' can put into a fuel something that isn't there to start with. And common sense should make you ask, if it is as simple as plugging in a filter or wrapping a big magnet around the fuel line, why aren't the oil companies using the technology during manufacture of the petrol to give us 'pre-treated' fuel?
Let me describe a typical one aimed at people concerned with lead free fuel. Its a nylon net bag full of lead pellets, and its advertised for £14.99, with the slogan "Put the Lead back in YOUR fuel - no need for expensive additives or costly conversions. Our product puts the lead back into your fuel for thousands of miles, for a the price of one fill-up. Our revolutionary product contains micro-coated lead alloy pellets that replace the lead removed by legislation. The special coating and alloys in the lead control the rate and concentration of 'dosing' so that you always have the right amount of lead in your fuel.........."
Now, the net is nothing more than a nylon fruit net, and the 'specially coated and alloyed lead pellets' are nothing more than the shot that is used in industrial cleaning processes, or even split and sold as fishing line weights. Selling for £14.99, the mark up is HUGE. Well, there is a lot to be said for market forces and charging what the buyer is prepared to pay, but basically, these things are a con.
There are a lot of variations on the theme. The 'specially coated lead pellets' can be in an inline fuel filter housing, or set into a tablet of plaster of paris, but the idea is the same. They LOOK like they will do the job - but they don't.
The wording of the adverts are very clever. Sure, they put lead into your petrol. Lumps of the stuff, and they sit there and the fuel flows around them and that is about it. And by putting one of these widgets you have done what it says, put the lead back into your petrol. And they do carefully control the level of 'dosing', they control it at zero.
As I said earlier, the lead that used to be in petrol was not metalic lead, but ionic lead or lead in volatile compound. Metallic lead itself is pretty inert and wont dissolve in petrol.
I have a theory that most of these 'widgets' rely on the fact that there is a lead memory effect in the engine from using leaded fuel previously, and if the engine does go wrong, then they can give you your £15 quid back and leave you with a thousand pounds worth of engine repairs, or merely say that there is no evidence to suggest that the 'widget' is in any way directly responsible for the damage, and site poor maintenance, old age or any other of a hundred maladies that can afflict old engines, to keep your £15 quid and get out of paying any damages.
But then I am a sceptic, as I've said. You pays your money and you takes your chances - personally I wouldn't, but if you do, that's your look out. Just don't say I didn't warn you.
So, onto other courses of action. Well, the best solution, has got to be a proper 'unleaded' conversion. The lead was there in the first place to lubricate the valve guides and seat and prevent some knock. Most engines can be converted to run on unleaded fuel with a modified cylinder head. The conversion may involve replacing the valve guides, possibly the valves, and maybe even some cylinder head 'porting'.
There is plenty that can be done. What, how and how much, are all very much up to you and the company you get to do the work. But, the mods do work and are permanent. Its a one time cost, and you don't have to worry about it again.
But what are they going to do, and how does it work?
Starting with the valve guides, here the lead is acting as a lubricant. The metal of the valve guide can be replaced with something with a self lubricating property. Some conversions may use a high grade cast iron, that has a very high carbon content, so it actually more like steel, but in actual fact, the carbon will 'sweat' out of the iron as graphite, which is a lubricant. This material was actually developed for helicopter gear boxes, where they must be capable of loosing their oil and not seizing. A helicopter that has its gear-box seize at 10,000 feet, will drop like a stone, so these high carbon irons are pretty good. Other alternatives include porous irons, or even 'sintered' alloys. These don't have any self lubricating properties, but will let engine oil seep through them from the rocker gear, and keep the valve stem lubricated that way. The amount of oil that is allowed through being so small that you wont notice any huge oil usage or white smoke, but its enough to stop the valve stems wearing too quickly. And then there are other self lubricating alloys, that have soft metals in them that will lower the friction on the valve stem.
Some of the most advanced valve guides actually use a sintered 'alloy' that is both mildly poorhouse and contains a mixture of self lubricating metals, both iron based and phosphor bronze based, to get the best of everything.
Actually I believe that British-Leyland, were at the fore front of this technology about thirty years ago. I know that they used a sintered alloy for the rockers of the Metro engine, and I have a feeling that they used sintered valve guides in the last of the push rod engines used in the Mini & Metro, in the late eighties and early nineties, when they had to make the engines capable of running on lead free.
Any way, next up, valve seats. Bit more tricky as they have to form a seal between the valve and the port in the cylinder head. There isn't much that can be done to make them self lubricating, so its down to finding a material that is less prone to wear and can withstand the temperatures and pressures better. Consequently, the usual course of action is to fit valve seats of a higher grade of metal that is normally also harder.
That may be sufficient, on its own, but sometimes you may need to have a different grade of metal for the valve itself, either to match the metal of the valve seat, or because the material of the standard valve will still wear or melt under the higher loading.
So, that lot should take care of the problems associated with the lack of leads lubricating properties, but it may not completely effect a cure.
I said that lead boosted the fuel's 'knock' resistance, and that the octane rating of unleaded was the same as for leaded, so it shouldn't be a problem.
Well, that's not QUITE accurate, because there's more to it than just the octane rating. Different fuels burn differently. Deisel for example burns a lot hotter and more slowly than petrol. Methanol, burns more slowly, and a lot cooler than petrol. And they can all burn at different temperatures and different speeds depending on the mixture strength and how fast the engine is turning and lots of other factors.
With the change from leaded to unleaded, the most significant difference is that the ignition timing needs to be changed because of a slight difference in the volatility of the fuel, but there are all sorts of things that can happen inside the engine's combustion chamber.
Sharp edges can induce turbulence into the charge as it burns that can increase or reduce the rate of burn, or can create a localised 'hot-spot', that will propagate detonation.
In some unleaded conversions, the engineering works that undertakes the job can go to the lengths of reshaping the combustion chamber itself, to put in edges to promote or reduce turbulence, or eliminate potential hot spots. This kind of detail is almost into the realms of craft rather than science, but it can pay dividends on the longevity, performance and reliability of an engine.
Any way, the conversion supplier will be able to tell you how involved the job might be on your particular engine, and how expensive. Some of the cheaper conversions may only do a minimum of work to enable you to use unleaded fuel, and expect you to suffer a small loss in performance as part of the price. Some may be far more thorough, and do a lot more to maintain or even improve the engines performance over standard, on unleaded fuel.
And it is quite common, given the expense, for people to ask for an unleaded cylinder head conversion plus 'stage one' porting at the same time.
But the choice on that one is up to you. Its a permanent solution, but involved and often expensive, and you may want to think about whether you just want to get the cylinder head modified to allow unleaded fuel to be used safely, or if you want to go further and do some power tuning work as well.
Which leaves the last option. Rude, crude and socially unacceptable - but effective. Ignore the problem. Given the lead memory effect, you can probably run for quite a long time before the lack of lubrication promotes serious wear in the engine. If you adjust the timing and mixture to get the engine running right, and keep a close eye on the tappet adjustment, you might not see much of a problem - and when you do, well, you have a choice. It will probably be the cylinder head that's worst effected, so you may get a bit more life by merely replacing the cylinder head for a second hand item, and running it like that until that one breaks. Or you might decide to replace the engine altogether and do likewise, or pull it out and overhaul it completely, and incorporate a lead free head into the rebuild.
But overall, the answer is that the loss of leaded fuel isn't anything to panic over - there is plenty that can be done to solve the problem. Even if you have a rare vehicle and can't find any-one who offers an unleaded conversion for it, there are still specialist engineering companies that may be able to fit harder valve seats and new guides and maybe some other bits and pieces to make it work, and ultimately, if you have to, you can use a lead replacement additive.
Just avoid the 'widgets'!