From: Electronic Telegraph, 3rd April 1999:

For up to eight million British drivers. the forthcoming ban on leaded petrol doesn't necessarily mean a choice between an expensive engine conversion or scrapping that old car. In fact, as Malcolm McKay reports, it might be possible to run it even more cheaply than before.

IN this section on December 12, we reported on the tests being carried out at the Motor Industry Research Association (Mira) to see if additives or devices that claim to allow any car to run on unleaded petrol actually work. Cynics expected all the products tested to fail - but the Federation of British Historic Vehicle Clubs (FBHVC), which organised the tests, has announced that four have passed: Millers VSP Plus, Red Line Lead Substitute, Superblend Zero Lead 2000 and Valvemaster.

Most surprising of all, the four products are priced so that, when mixed with premium unleaded, your fuel will cost less per litre than leaded petrol does now.

For the 1.2 million classic cars and five to seven million more recent vehicles on British roads that require the protection of leaded fuel, this is, on the face of it, brilliant news.

There are, however, complications and reservations. Many chemicals are involved that don't necessarily mix well with each other, and every car and driver is different. To help, here is our guide to driving older cars into the next millennium.

What does lead do anyway?

TETRA-ETHYL lead was first added to petrol in the Twenties, chiefly to increase its octane rating. Put simply, this allowed engine builders to make smaller, more powerful engines by increasing the compression ratio without the engine being destroyed by pinking (or knocking). Then scientists realised that, as well as stopping the pinking, the lead additive reduced the valve seat recession that made frequent adjustment of tappets and grinding of valves necessary on hard-driven engines.

What is valve seat recession?

IN CONDITIONS of extreme heat and high revs (a hard-driven, fast-running engine), the exhaust valve momentarily welds itself to the valve seat at its hottest point and then tears off a tiny chunk of the seat as it re-opens. The minute specks of metal stuck to the valve grind away at the seat as the valve opens and closes many times a second.

Exhaust valves and their seats get exceptionally hot during hard driving due to the huge volume of newly burnt gas passing through. Inlet valves do not suffer as they are cooled by the fresh air/petrol mix they let in to the cylinder.

Lead added to petrol deposits lead oxide on the exhaust valve seat, forming a microscopic film that better dissipates the heat and prevents the momentary welding of the valve to its seat.

What else combats valve seat recession?

AN EFFICIENT cooling system helps to reduce temperatures throughout the engine, exhaust valve seats included: if your engine is inclined to overheat, now is the time to get that radiator repaired or replaced. If the cylinder head is taken off for any reason, make sure all the water passages are properly cleaned of silt and sludge.

Gentle use is a good way of avoiding problems; if you drive carefully and don't hammer down motorways, you're unlikely to get any problems with unleaded petrol. Valve seat recession kicks in progressively above 3, 000rpm, an engine speed that many gently-driven cars, especially large-engined ones, seldom exceed.

The ultimate answer is to have hardened valve seats fitted: the use of harder steel alloys makes them almost completely resistant to the momentary welding that leads to wear. The number of engines that have hard seats already is far higher than most people realise: Brico Engineering, British maker of valve seat inserts, confirms that every seat it has made for insertion in aluminium-alloy cylinder heads since the 1940s is technically hard enough to cope without lead in fuel. Valve seats are now made of even harder material, but older seats should be up to the job.

Why is lead being banned?

GOOD QUESTION. Lead started to be phased out in the Seventies in California, when catalytic converters were invented to clean up exhausts: lead destroyed the converters. Some studies suggest that lead retards the brain development of children in areas of high pollution, though other experts argue that leaded petrol's role in this is not proven. Nonetheless, the argument that lead is dangerous to health has been allowed to run unchallenged. Some additives used in unleaded fuel can be carcinogenic, however. Whichever studies you believe, the decision to ban lead has taken the choice out of your hands: starting in America many years ago, authorities have progressively banned leaded petrol in favour of unleaded with expensive, inefficient catalytic converters to remove the worst of its pollutants. That ban hits the UK on January 1, 2000.

Will my car run on unleaded?

PROBABLY! Check with the manufacturer or a main dealer and beware of opinions expressed by people who stand to profit by modifying your engine. If the manufacturer says it's OK fine. If not, don't give up yet. If it's a post-war car with valve seat inserts, such as in an aluminium-alloy cylinder head, it might be OK without lead. If you do choose to risk running unleaded in such a car without modifications, you will need to keep a close check on the valve clearances and listen out for pinking. If it has a cast-iron cylinder head with soft valve seats, read on.

What if my car needs high octane but not lead?

PREMIUM unleaded is 95 octane; high compression engines require 97 octane, as in four star, to prevent pinking. Super unleaded at 98 octane is fine, but it's expensive and fast disappearing from forecourts. Some petrol companies are considering increasing the octane of premium unleaded to 97, so watch the pumps.

Lead Replacement Petrol (LRP), which will progressively replace leaded this year, will be 97 octane; but there's no British Standard for it yet so stick with leaded until there is.

It might be possible simply to retard the ignition of your engine (though this can cause higher engine temperatures, which brings its own problems) or to lower the compression ratio by fitting an extra head gasket. Better though, to use an octane booster with premium unleaded: it will allow your engine to run as efficiently as it was designed to and the cost will probably be considerably less than the difference between premium and super unleaded.

Millers VSP Plus is the only one of the approved valve seat protectors that's also an octane booster.

I need leaded: what should I do?

IF YOU intend to keep the car for a very long time, cover high mileages at high speed or indulge in motorsport, it is probably worthwhile getting hardened valve seats fitted, especially if your engine is coming apart for a rebuild anyway. First, though, ask experts such as owners' clubs, because a few older engines cannot be fitted with hardened seats or might be irretrievably damaged in the attempt. The cost will vary from a few hundred pounds for a simple four-cylinder engine to several thousand pounds for something more sophisticated, but there's little sense in rushing out and spending unless you've actually had a valve burn out.

It should also be noted that fitting valve seat inserts to any cylinder head is not a job for the inexperienced. Fitting, locating and ensuring such inserts stay in the head takes skill, mainly because of the differences in material expansivity. There is also the matter of valve guides, which might need to be of a different material or machined with oilways to ensure adequate lubrication when using unleaded fuel. Our advice is to pick your engineering company carefully.

If you use the car gently or don't intend keeping it long, you could just use unleaded. Cars can run for years on what is known as "the lead memory effect". This is a coating of lead built up on the valve seats that protects against serious erosion for up to 10, 000-15, 000 miles, even with hard use. With gentle driving, the lead memory effect might outlast the life of the car.

If you want to look after your engine without restricting your driving, use one of the four additives that have been approved by the Federation of British Historic Vehicle Clubs; use it only with premium unleaded, and smile as you save some 3p per litre compared to the current price of four-star: combined with the existing residue of lead, your valve seats should last for 40, 000 miles or more.

If your car requires higher octane than premium unleaded's 95 rating, use Millers VSP Plus, which provides full valve seat protection and boosts the octane; it still works out no more expensive than leaded petrol.

Leaded fuel will still be available, chiefly for historic motorsport use, but it must not exceed 0.5 per cent of total sales. It will be expensive; the FBHVC is currently discussing distribution arrangements with the Government and petrol retailers.

What about turbocharged and fuel injected engines?

THERE IS some evidence to suggest that seals in older fuel injection systems, such as Lucas PI systems on Triumph TR6s, are affected by unleaded petrol. If you get any problems, suitable exchange metering units are now available from specialists. In Sweden, damage to turbocharger vanes has been blamed on sodium-based LRP.

What about LRP?

LEAD REPLACEMENT Petrol is the petrol companies' answer to the ban on sale of leaded petrol and will become widely available as four star is phased out. It will have the same octane rating as current leaded petrol and will contain an additive that resists valve seat recession, though probably to a lower concentration than in the additive mixes tested at Mira. The British Standard for this fuel is in draft form only at present; it identifies manganese, potassium and phosphorus as suitable additives.

Don't be tempted to fill up with LRP and dose it with additives for good measure: it might do more harm than good, as different additives can cause adverse chemical reactions and lead to corrosion.

What's the secret of these additives?

SURPRISINGLY, the four successful additives do not all use the same chemical formula. Millers VSP Plus is manganese-based, and is the only one currently to double as an octane booster. Redline Lead Substitute is sodium-based and has been used in America for 15 years. Superblend Zero Lead 2000 is potassium-based, a formula used in Europe for several years. Valvemaster is phosphorus-based; it has been widely used for the last five years in New Zealand and is the only substitute to have passed the Australian Standard.

What was the test?

CAST-IRON A-series engines (as used in Austin A30s and Minis and Metros) are acknowledged to be among the most vulnerable power units for valve seat recession when using unleaded fuel - and that is why they were chosen for the test. A special batch of cast-iron cylinder heads without hardened inserts was donated by Rover. The engine was run with a new cylinder head fitted for each test, for 50 hours at 3, 800rpm on two-thirds load, 30.8bhp (23kW), with valve-seat recession checked and tappet clearances adjusted every 10 hours; then it was run on full load, 48.3bhp (36kW), at 5, 500rpm for 20 hours, checking and adjusting every five hours. The test was certainly severe, with 1.19mm recession occurring on untreated unleaded fuel, leaving the cylinder head unusable. A test using leaded fuel, however, showed negligible valve seat recession; to pass, a fuel treatment was permitted to show a maximum 0.3mm valve seat recession over the whole test, or 0.13mm during the first 50 hours.

But while the FBHVC and Mira have taken all precautions to ensure their findings are fair and representative, the use of bathtub-type A-series cylinder heads creates some variables that might have escaped consideration.

Heat build-up around the exhaust valves of different engines will depend on the port, valve and guide design and this will affect the level of valve seat recession. In addition, the cast iron used in cylinder heads differs in hardness. David Thirlby, editor of the Vintage Sports Car Club's Bulletin, points out that if the hardness of the tested Rover cylinder heads had been published, it would have provided at least a base line for different owners' clubs seeking to conduct further research.

Which additive came out best?

THERE'S very little in it, though Millers is the only choice if you need an octane boost. It works out at about 8p per litre of treated petrol; Superblend (which produced the best results in the Federation tests) is 5p, Redline and Valvemaster just 3p. Even better results may be obtained by using a greater concentration; for example, Redline asked for its test to be at its standard recommended dosage, even though the bottle recommends a double dose for high speed/load motoring. Do not mix additives or exceed the recommended dose: excessive concentrations might cause deposits that make valves stick open and damage the engine.

What about the rest?

AT PRESENT, the FBHVC cannot reveal which treatments failed the test, or which declined to submit their products. This might change in the future, and it could be that more tests will be carried out, but for now there is little point in risking an untested product. The FBHVC/Mira tests were conducted to extremely high standards, according to standard motor industry protocol, and were independent (suppliers paid a fixed £5, 000 fee to the FBHVC, which then paid Mira).

It is known that six other additives and two fuel-line devices were tested, and that some produced worse results than premium unleaded and actually increased wear. Ian Edmunds, FBHVC fuels committee chairman, says: "There is no evidence to show why fuel-line devices, such as those containing tin cones, should work."

Will what I buy be what was tested?

APPROVED products will carry the FBHVC approval crest, and the Federation will police products by regular sampling to ensure the chemical composition and concentration are not changed from the batch tested.

Where do I get it?

ADDITIVES are already available from some petrol stations and car accessory shops; they will become much more widely available as leaded petrol is phased out. Contacts to check on availability are:

Millers: Irene Crowther on 01484 713201, fax 721263. Stocks of 250ml bottles (to treat 45 litres of petrol) should be in the shops in May.

Red Line: 01732 866885 (Scotland 01968 673127). Now available are 355ml bottles (545 litres).

Superblend: 0116 291 1700. Selling 500ml bottles (150 litres) by mail order.

Valvemaster: 01908 372611, fax 273613. Will be available in one-shot applicators to treat 20 litres of fuel as well as in 250ml bottles (400 litres).

FBHVC: PO Box 2506, Henfield, West Sussex BN5 9QW.