As the engines in most classic cars were designed to run on leaded petrol, which was withdrawn from sale in 2000, what precautions need to be taken when running them on modern unleaded fuels?
Lead was used as an additive in petrol to produce higher-octane fuels that have improved resistance to ‘pinking’ or ‘detonation’ (when fuel explodes in an uncontrolled manner in the combustion chamber rather than being ignited into a controlled flame by the spark plug). It was also later discovered to protect the valve seats from wear. Some licensed garages are allowed to sell a limited amount of leaded fuel for use by historic vehicles, but they are few and far between and prices are considerably higher than for regular unleaded petrol.
Super unleaded petrol with a higher octane rating than the standard 95 sold on British forecourts is available from suppliers as diverse as Shell and Tesco these days – and some classic car engines designed to run on 100 octane can benefit from its use.
In general, pre-1992 cars designed to run on leaded petrol may need to have their ignition timing adjusted if they are to avoid problems with pinking on standard 95RON unleaded.
Older cars with valve seats cut directly into cast-iron cylinder heads or blocks can suffer excess wear of the seats if subjected to hard, high-speed use. The solution is either to have hard-alloy valve seats or an exchange cylinder head fitted. That’s a considerable expense – a cheaper alternative is to use a proprietary branded additive in your petrol. There are a number of firms who supply bottles of beneficial stuff with various claims as to their efficacy for classic car engines. We’ve listed the additives endorsed by the Federation of British Historic Vehicle Clubs (fbhvc.com) below – but if using them, take care. Mixing can be an acquired art in small volumes – you don’t want to overdose your engine!
Millers VSPe Power Plus (from millersoils.net)
A petrol fuel treatment claimed to have lead-replacement and octane-improvement qualities, as well as providing protection against ethanol. Ethanol is an additive which is commonly used in modern petrol and at increasingly high percentages – unfortunately, it can corrode gaskets and other soft fittings in the engine’s fuel system.
Red Line Lead Substitute (from redlineoil-europe.com)
A lead substitute claimed to prevent damage to engines designed for leaded petrol, plus clear deposits in carburettors and fuel injectors, and to be safe for catalytic converters. But it’s produced for racing or off-road use only.
Castrol Valvemaster (from castrolclassicoils.co.uk)
This additive has undergone a valve recession test by an independent test house on behalf of the Federation of British Historic Vehicle Clubs – the results indicated that the level of valve seat protection it provides is likely to be adequate for all normal driving. Castrol’s Valvemaster Plus provides an added octane boost when added to unleaded fuel.
Tetraboost (from tetraboost.com)
Tetraboost ‘E’ Guard 15 claims to allow the user to mix ‘genuine leaded four or five-star fuel’ and to offer protection from up to 15% ethanol content in fuel.
The bottom line with these fuel additives is that only certain cars will derive any serious benefit from them. For many drivers of classic cars, modern unleaded and super unleaded fuel will not provide any major problems, unless their vehicles are regularly pushed to the limit of their performance. It all depends on the constituent parts of your engine and fuel system – if you don’t know, contact the car club that deals with your respective vehicle. The thing to remember is, once you’ve found a particular fuel or additive that your car is happy with, stick with it and you should enjoy your classic motoring for many miles to come.