Lead Substitute Gas Additives
Protecting your MG from Valve Seat Recession and Knock
Why Lead? Organic tetra-ethyl lead and tetra-methyl lead was first added to auto fuel in the late 1920’s to raise its octane rating and so allow higher compression ratios without the damaging effects of knock; also called pre detonation, pre ignition, pinging or pinking. An unexpected side effect of the lead compounds deposited in the combustion chamber was that valve seat erosion was significantly reduced, allowing engine manufacturers to eliminate the costly process of putting hardened valve seats into the cast iron block or head. The lead is often said to act as a valve cushion, but in reality, valve seat recession (VSR) begins with local welding of the valve to its seat. The problem then becomes compounded as seat material attaches itself to the valve, forming an irregular surface capable of further damage by grinding more valve seat material away as the valve rotates during operation. When leaded fuel is used, combustion causes deposition of lead lead oxide, forming a barrier between valve and seat, almost eliminating VSR.
Europe Losing Lead. Leaded automotive fuel was finally removed from European Union markets at the end of 1999, some 12 years after its final demise in the United States. There is justification for the late withdrawal of lead in Europe and the concern to those there with older vehicles only designed to run with leaded fuel. Low energy prices in North America led to automobile engine development taking a wholly different evolutionary branch from those in most of the rest of the world. Horsepower is proportional to both torque and engine speed, and whereas other countries chose to get their power from high engine revolutions, the US chose high torque provided by high swept capacity. Unlike the big US engines, which had large pistons with long strokes that travel relatively slowly, Europe made small, high revving engines with valves which not only run hotter, with the potential for increased weld damage, but open and closed more often, adding to the grinding effect of any damaged valves. Moreover, to get the performance from their small engines, European manufacturers tended to use higher compression ratios requiring higher octane fuel in order to counter knock. (Note that in Germany, the dominant VW engine, found also in Porsche and other Auto Union vehicles, had an aluminum head, so separate hardened steel valve seats were always a necessary feature of their cylinder heads. This may also have been true for engines produced in France by Citröen and Renault).
FBHVC Tests. Although the fuel companies in the UK and other countries are planning to make a lead replacement petrol (LRP) available, these products are likely to be simply unleaded fuel, with additives similar to those you and I can buy over the counter, added to the mix. The Federation of British Historic Vehicle Club (FBHVC) decided that their members deserved better information about the efficacy of these lead substitutes than was readily available. To that end, they commissioned the well-respected Motor Industry Research Association (MIRA) to run a series of tests to determine the additives’ effect on VSR.
Spridget Engine Test Bed. The platform for the tests was the Rover A series engine which has powered a number of vehicles for over 40 years. Versions of this engine without hardened valve seats are considered to be particularly susceptible to VSR. Before the tests were run, some comparative work was done to demonstrate the effect of lead in the fuel. During the 70 hour test cycle the head run with unleaded fuel exhibited an incredible 1.19mm (47mils") of VSR, compared with negligible erosion for the leaded fuel. To gain endorsement by FBHVC, an additive had to limit VSR to 0.3mm (12mils") over the full test cycle.
Tests Criticized. It should be said that FBHVC’s test plan was not without its critics. Of 40 products invited to take part, only 12 companies paid the £5,500 entry fee to do so. Some suspected the reproducibility of the tests, feeling that the process was akin to a lottery, and so chose not to enter products rather than risk losing their reputation should their product not become an FBHVC endorsed additive. The other major criticism, which FBHVC fully acknowledge, is that the tests were limited to measuring VSR and no attempt was made to check for collateral effects, such as corrosion and environmental hazards. The tests having been completed, the print and web press consensus seems to be that FBHVC should be commended for shining some light where there was none before, even if the did not have the resources to illuminate the whole subject.
The Oscars Go To…. FBHVC gave their endorsement to 4 products. Interestingly, each of these products uses a different additive: -
|Millers VSP-Plus.||Lead Substitute & Octane Booster|
|Red Line||Lead Substitute|
|Superblend 12 / Zero Lead||Lead Substitute|
Only one of these products, Red Line, is available in North America, but it is worth studying all the endorsed FBHVC products to see what US and Canadian MG owners can learn from the British tests.
Millers VSP Plus contains manganese, a well-known fuel additive in the US where it is sold solely for its octane boosting qualities. The FBHVC test result, showing that it also works to reduce VSR, is a revelation, but perhaps not a surprising one. Manganese does leave its oxide coating behind after combustion and so should offer some buffer to the interface between the valves and their seats.
In the USA, manganese, or MMT as it was know, was added to gasoline in the late '70's to raise octane. Today, Bardahl Octane Booster and CD Octane Booster are readily available products in North America which, like Millers VSP Plus, are based on manganese. They claim an octane boost of up to 4-6 units, which should help those who have found it necessary to retard their engines to avoid knock. Using Manganese can be quite alarming, its oxide looks similar to iron oxide, that is rust, and when it appears on spark plugs and the inside of exhaust pipes, it can give a false impression that some dreadful water problem is corroding the motor from the inside out.
Red Line, the only endorsed North American product, contains sodium. This is the predominant lead substitute used in the US, being the active agent in Bardahl Insted O’Led and CD-2 Company's Lead Substitute. These two products are very readily available in the US and Canada. The other major producer of lead substitute, STP, declined to disclose the agent in their product, but in an e-mail stated, "STP Lead Substitute does not contain potassium, phosphorous, manganese, or sodium". Without further information, it is neither possible to judge the benefits nor the risks of their product.
Sodium has been much criticized in Europe where it is considered to be the cause of hot metal corrosion. Much of the evidence of this has come from the Swedish Army whose Ford V6 engines were said to be wearing much earlier with sodium based LRP than they did with leaded fuel. Also in Sweden, owners of early Saab Turbos, which did not have hardened valve seats, were said to be experiencing turbine corrosion due to sodium LRP’s. Whether any of this is relevant to MG’s is debatable.
Superblend 12 / Zero Lead contains potassium. I am unaware of any lead substitute available in North America that is based on potassium.
Potassium has been cited in some quarters as a cause of inlet valve gumming, but any such effect is most likely dependent on the overall fuel - additive formulation. It will be the additive used in Shell and other European LRP’s. It was once used as a component in Canadian gasoline after the withdrawal of leaded, but was phased out in 1995.
Valvemaster contains phosphorous and is the predominant product in Australia and New Zealand.
Phosphorous was at one time the active agent in most US manufactured products, but the Environmental Protection Agency (EPA) has banned its sale for use for road use. It may well be available in industrial outlets for use in stationary engines like pumps and generators. Besides questions about its environmental toxicity, there have been accusations that phosphorous causes hot metal corrosion. Note: it should never be used in vehicles with catalytic converters.
The good reputation that phosphorous
has gained in Australia and New Zealand is relevant to 'Little British
Car' owners, similar vehicle engines being used in those territories as
Manganese as a VSP Inhibitor? The British Magazine Classic & Sports Car (C&SC) June 1999, which was a source for some of the supplementary information included here, added some interesting tidbits to the FBHVC press release. It seems that although the final pass criterion was 0.3mm, it was originally a lower value. Moreover, C&SC says that the VSR resulting from the potassium was just 0.06mm, one fifth of the target. Knowing that both phosphorous and sodium have proven themselves in independent tests in Australia and the US respectively, and that the very knowledgeable and respected Seattle based Bardahl company makes no claims for VSR reduction with its manganese based Octane Booster, one wonders if in an effort to get a reasonable selection of products passing, FBVHC included a marginal product when it endorsed manganese.
Dosage. It is also legitimate to question dosage. Why did 4 products pass and 8 fail? It is doubtful that they were all based on different chemicals, but MIRA used the products as directed on their packaging. One of the 12 was said to make VSR worse than unleaded alone!
Were the tests severe enough? Many would consider a VSR of 0.3mm (12mils") after 70 hours to be pretty scary in itself. That 70 hours actually consisted, S&SC says, of 50 hrs @ 3,500 r.p.m., 2/3 load and 20 hrs @ 5,500 r.p.m., full load. In a Spridget (which remember, has an A series engine like that tested) this equates to driving at 54 mph for 2,695 miles followed by 85 mph for 1705 miles. In an MGB, that's approximately the equivalent of driving at 63 mph for 3,150 miles (or 77 mph for 3,850 miles with overdrive) followed by 99 mph for 1,980 miles (or 121 mph for 2,430 miles with overdrive). That's a tough test (if not impossible)! VSR increases rapidly with engine speed so if you drive your MG at a rather more leisurely pace, then you should travel many more miles before the onset of significant VSR.
Get Ahead. If unleaded has already done its damage, as well might have happened over the last few years to North American owned cars, then a new (or reconditioned) head with hardened valve seats should be considered. The impending loss of leaded in the UK has resulted in several companies offering "unleaded heads" that come complete with new valves, springs and guides. Ports are often opened up a little to optimize performance. At less than £200 (~$320), even of they cost $100 to ship, they are competitive to heads sold in North America. Go to the bottom of the page for the List of Suppliers.
Stop the Knock.. While VSR is very damaging to an engine, knock can be disastrous. Petroleum fueled engines are designed to work with a controlled burn which starts from the spark plug, the flame front moving across the cylinder, expanding the gas as it does so. If the engine timing is correct, optimum pressure builds at just the right rate to push the piston down smoothly and evenly. As the engine speed increases, there is less time for the flame front to spread, and so automatic systems in the distributor, sprung loaded centrifugal weights and a carburetor fed vacuum diaphragm, advance the spark. Diesel engines, however, do not use a spark plug, the fuel/air mix detonating as a result of heat caused by compression and that already in the cylinder of an already running engine, (or the glow plug when starting a cold engine). Diesel detonation is much more rapid, occurring throughout the gas mixture with no true flame front. This sudden uncontrolled burning causes a large pressure wave and the characteristic knock heard from all diesel engines. Unfortunately, low octane petrol can also detonate due to the combined effects of the piston compression, the advancing pressure wave of spark ignited fuel and residual heat in the cylinder. So a second pressure wave, in opposition to that initiated by the spark plug can occur, producing knock, pinging or (to Brits) pinking. Knock has been compared to a hammer blow to the top of the piston. In an engine not especially designed to "diesel", it can put a hole in a piston and damage connecting rod bearings.
Remember that the original purpose of lead was to increase the octane rating and that most lead substitutes are ineffective against knock. If your MG exhibits knock when under load then there are a few alternatives. Retard the engine with consequent performance loss, use a higher octane fuel if available, or add an octane booster to the fuel.
All About Octane. First what octane isn't: it isn't a measure of the power available from a fuel or how hot the fuel burns, so using a higher octane fuel than a vehicle needs to inhibit knock, hits your wallet, but does not enhance performance. A fuel's octane number is simply a numeric indication of its ability to inhibit engine knocking. However, octane is measured in different ways, so care has to be taken when making comparisons where different systems are in use.
RON, MON and AKI.. MGB’s with high compression engines were listed as requiring Premium 98 octane fuel or above. However, this cannot be directly compared with the octane number found on the pumps in North America, which is rated differently. In Britain, the Research Octane Number (RON) is used to indicate a fuel’s octane. This number is derived from tests on an engine running at a constant speed of 1500 r.p.m., conditions that do not closely relate to those found in real situations. In order to address this disconnect with reality, the Motor Octane Number (MON) system was developed using a tougher test carried out at higher engine speed and temperature. In the US and Canada the two systems coexisted for a while -- causing much confusion. To resolve the matter the U.S. Cost of Living Council (CLC) index, better known as. Anti-Knock Index (AKI), was introduced and is simply the arithmetical average of RON and MON; so AKI = (RON + MON)/2 and is the number now familiar to motorists in the USA and Canada. Yet another measure may sometimes be referenced: Road Octane Number (RdON).This is considered the best predictor of octane but it is determined by running a vehicle on the road or using a chassis dynamometer, and it is too dependent on the actual engine under test. RdON is so close to AKI that they are often used interchangeably. There is no direct correlation between RON and MON, different formulations for fuels with the same RON number might well produce different MON’s. You can make a rough determination, however: for the high octane fuels we are concerned with, the difference between RON and MON, or the "sensitivity" as it is known, is about 10. If you know the AKI therefore you can add or subtract 5 to determine the approximate RON or MON respectively.
Taking Shell as an Example. In the USA Shell 93 (AKI) octane FormulaShell Premium is about the best found at the pump and is 98 RON. In Canada, Formula Shell Gold: 91 (AKI) is actually 95 RON, so Canadian "B" owners with vehicles requiring 98 RON could well need to address a knock problem. Furthermore, Shell say, "… when a vehicle gets older, …… build-up of fuel- and lubricant-related deposits can increase the fuel octane number a car requires to prevent engine knock. For this reason, if a car more than a couple of years old experiences engine knocking, the problem may be solved simply by moving to the gasoline blend with the next higher anti-knock index". So even US drivers may need an octane boost too. In the UK, Shell UK Ltd had a 4 Star, 97 (RON) octane LRP based on potassium available during October 1999.
RFG. There are further complications in the US where certain states (California, Connecticut, Delaware, Illinois, Indiana, Kentucky, Maine, Maryland Massachusetts, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Texas, Virginia, Washington DC and Wisconsin), in an effort to reduce automotive emissions, are mandated to use reformulated gasoline (RFG) because they fail to meet air quality standards for ozone. RFG has lower levels of volatile compounds and benzene and contains an oxygenate such as ether or ethanol. Oxygenates burn hotter and may well speed up VSR. Fuel companies all over Canada and the northern United States sell oxygenated fuels in wintertime to reduce carbon monoxide levels, but since most LBC's get hibernated, that may not be an issue. If your car is difficult to start, RFG may exacerbate the problem because its higher volatility makes it harder to get a rich mixture when using choke.
Following concerns about ground water pollution and also about Federal research which shows that MTBE, a compound in RFG, causes tumors in rats and may do so in humans, Maine has pulled out of the RFG program and California has also announced its intention to do likewise.
In May 1999, the U.S. National Research Council, speaking of RFG said, "....it is not possible to attribute a significant portion of past reductions in smog to the use of these gasoline additives."
In July 1999, a U.S. Environmental Protection Agency advisory panel, comprising diverse interests from environmentalists to oil industry executives and state regulators reported on safety concerns associated with methyl tertiary-butyl ether, better known as MTBE. They found that while reformulated gasoline has contributed to significant air quality improvements, MTBE poses a threat to drinking water. They said MTBE use in RFG "should be reduced substantially".
Do-it-Yourself. The ideal way to increase the octane rating of fuel to the optimum amount would be to experiment with different dilutions of the same brand of octane booster. This is not an easy task, since it requires logging the dilution already present, knowing the exact volume of fuel in the tank, having a precise measuring receptacle for the octane booster, a calculator to compute the amount required to take the dilution from the actual to the desired concentration and a Ph.D. to know what buttons to press.
Me? I will use a product like Bardahl Instead O’ Led Gold, which is a combination product of their lead substitute and their octane booster - if I can find it that is. In my region I visited the large auto parts dealers: Murray’s, Auto Zone, Pep Shop Boy’s and Glendale to no avail. I called Bardahl and a very nice lady told be how I could get it by mail order, unfortunately, for rather more than the retail price. She also told me that some Rite Aid drug stores carry it. Remember to get some Tylenol while your there too; you may need it to stop the knocking noise in your head.
|Bardahl Manufacturing Corp.|
|Tel:||+1 (206) 783-48511|
|Tel:||+1 (888) BARDAHL|
|CD -2 Company|
|Tel:||+1 (708) 563-3600|
|Classic & Sports Car|
|Tel:||+44 181 943 5995|
|Red Line Synthetic Oil Corporation|
|Tel:||+1 (800) 624-7958|
|Shell Canada Limited|
|Tel:||+1 (403) 691-3111|
|Shell Oil Company|
|Tel:||+1 (800) 231 6950|
|Shell UK Limited|
|Tel:||+44 171 257 3000|
|Tel:||+1 (703) 846-3000|
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List of Suppliers
for "unleaded heads".
|The MGB Hive|
|Tel:||+44 1945 700500|
|Fax:||+44 1945 700130|
|Mech Spec MG Centre|
|Tel:||+44 1909 482775|
|Fax:||+44 1909 478346|
|Derwent Sports Cars Limited (trading as Ron Hopkinson)|
|Tel:||+44 1332 756056|
|Fax:||+44 1332 572332|
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Please contact me if you have questions, contributions, comments or corrections.
Member of Windsor-Detroit MG Club
Last updated March 16, 2000
©Rick Astley 1999