That is no longer the question, our minds have been made up for us by F2J Prescott and the fuel companies.

I went along to the Institution of Mechanical Engineers November meeting in Basildon to hear what Dr. John Bennett, the man responsible for fuel research and development at Ford Motor Company, had to say about the future.

You will have no doubt noticed the gradual demise of "Super unleaded" from the pumps. It is also now almost impossible to obtain 4-star made to BS 4040, the change having already been made to lead replacement petrol (LRP) by all the major fuel companies as legislation has dictated that all lead must be removed from the supply chain by 31/12/99.

Great confusion is being created by each supplier calling their product by different names and not disclosing (except under duress) which chemistry they are using to replace the lead.

The inclusion of lead in petrol has two benefits;

To improve the "octane number" (RON) of low cost gasoline fractions allowing greater efficiency from the engine.

To reduce valve seat regression (VSR) by coating the valve seat with lead compound thus "cushioning" the impact of the valves as they close.

For some time the amount of lead in gasoline has been progressively reduced as advances in fuel fractionation take place, so much so that the amount included had negligible effect on RON. The level now is just sufficient to prevent VSR in the majority of engines and is believed to be of the order of 10pm in 4-star petrol of 97 RON.

Super unleaded was made to a BS (the number escapes me ) and was of 98 RON minimum. LRP consists of 97 RON unleaded gasoline with an additive to reduce (note not prevent) VSR and there are four different chemistries available so far,
1. Potassium (K) metallic
2. Sodium (Na) metallic
3. Manganese(Mn) metallic
4. Phosphorous(P) non-metallic

Sadly there is no likelihood currently of LRP being made to a British (or European) Standard because the fuel companies could not agree for commercial reasons to use the same chemistry and of course, there are differences in effect between them all. Independently, they have in the UK decided to use the K based chemistry but the situation is different on the continent.

The differences in effect can be described in two ways depending on the point of view; either motor manufacturer or consumer. With catalysts now being fitted to all cars sold in the UK since 1992 and recently enacted legislation dictating that manufacturers must be responsible for emissions from their cars being within specified limits for 5 years, they clearly do not want any damage to catalysts.

Broadly speaking, non-metallic additives rapidly poison catalysts while metallic additives do so less rapidly. There is clearly an axe to be ground by the motor manufacturers to lobby for a metallic additive in order to cater for the idiot few who might try to use LRP when they shouldn't and the early attempts at LRP several years ago in Scandinavia used a Na based additive on cost grounds but with occasional disastrous results to the turbochargers of Saabs & Volvos worked very hard. A highly corrosive "glaze" was formed which dissolved the rotors.

The Mn based system can have some slight benefit in increasing RON and it was stated by a member of the audience that Castrol are marketing an additive based on Mn to improve octane rating as well as reduce VSR. Dr. Bennett's view, not Ford's, was that such claims could be misleading because of the negligible effect of the amount of RON improving additive present. The consumer would want the best possible performer irrespective of chemistry & effect on catalysts because engines needing LRP do not in the main, have catalysts fitted.

The major fuel suppliers in the UK fortunately for us have concentrated on K based chemistry, but that is not necessarily the case on the other side of the channel as Ford's experience is that the fuel companies do whatever is commercially best on a given day. This means for example that Esso may use K additive on one day and Mn on another. The largest majority of UK LRP will contain the K additive at a level of 8ppm (just about enough to reduce VSR) and this is what Esso, Texaco, BP and Shell are supplying to us nutters who like old cars & bikes. The drawback however is that 8ppm is not enough to prevent VSR.

Tests on vehicles driven flat out for extended periods carried out by a research organisation in Germany found that at 8ppm K additive, a 4 cylinder engine (believed to be the Rover A series; the modern engine most prone to VSR) had 2 of the 4 exhaust valve seats damaged. 16ppm was required to reduce VSR to an acceptable level and the only way to bring this level up is to add it yourself. One word of warning. Do not overdose your fuel! All sorts of other problems may occur ranging from sticking valves and plug fouling to incompatibility with some rubber based fuel system components. Once you have started to use one type it is better to stick to it to avoid any potential incompatibility.

The Federation of British Historic Vehicle Clubs commissioned tests on a number of over the counter additives and only four in alphabetical order have passed these tests;
1. Millers VSP Plus (Mn based)
2. Red Line Lead Substitute (Na based)
3. Superblend Zero Lead 2000 (K based)
4. Valvemaster (Believed to be P based).

P based systems must not be mixed with any of the others; severe compatibility problems will occur, especially with LRP using K chemistry.

Much publicity has been given to "fuel catalysts" that are either fitted in line or drop into the fuel tank. There is no evidence whatsoever that these devices offer anything other than a possible extension to the "lead memory" phenomenon that exists anyhow. This memory, (remember the pre-catalyst 1 tank-full in 5 advice?) is as a result of lead deposits being chemically combined with the valve seat material and under careful driving conditions should last for more than 3000 miles. For these "catalysts", 3000 mile warranties are common and it is easy to see why, but for a high-performance classic car or bike used as they were intended, they are worse than useless because you may have forked out £70.00 plus and still end up with a damaged engine. The harder an engine is driven, the less "memory" will remain and the curve is not linear! An engine used in arduous conditions may lose it's "memory" after as little as 700 miles and once lost, it cannot be regained as there is no such "memory" imparted by the alternative chemistries. Some one-make car clubs are doing their members a great dis-service by recommending these "catalysts". The lead memory is also affected by the current crop of additives and so the "catalyst" user may be lulled into a false sense of security by not noticing any changes for quite some time by which time of course the seller will have made his money and long since disappeared.

The speaker's last slide was entitled:

"What will I as the owner of five classic motor cycles (BSA's) be doing?"

His answer was to use LRP to take advantage of the higher RON value (97) compared to Premium unleaded (95) and keep an eye on VSR by measuring valve clearances after the 2-3000 mile period. For competition, his recommendation is to have an unleaded conversion carried out when valve clearances become noticeably wider.

For really old cars, like my Morris 8, with side valve engines, there is no option but to use LRP or to use an additive with 95 RON unleaded and put up with any VSR. Low compression engines should not really notice the drop in RON because they were designed before the use of tetra-ethyl lead as an octane improver became commonplace. It was the RAF's wartime requirement for ever more powerful aero engines that drove the fuel companies in that direction originally and the usage crept into road fuel as the quest for speed and efficiency began in the fifties.