THE TRUTH ABOUT UNLEADED

TO : MARQUE-BY-MARQUE GUIDE

ADAPTED FROM "THOROUGHBRED & CLASSIC CARS" MAY 1998

There are many good reasons why this shouldn't happen, but it will: now we need to know how to run our classic cars. It's not as bad as you might think. For most of us, there will be no need to take any action for many years. During extensive research for this feature, we found no consensus of opinion on what can and cannot, should and should not be done to classic-car engines when four-star finally disappears. Don't believe opportunist mechanics who claim that because your car is over 20 years old, it has to have $$$-worth of conversion. Many old cars need no conversion work at all, while others can be converted. Equally, don't believe those who say that pre-war cars are OK because there was no lead in petrol before the war; modern unleaded petrol is very different from pre-war fuel - it burns at higher temperatures, and hard-driven pre-war cars can still suffer. This guide should help you decide how to keep enjoying your classic well without breaking the bank.

THREE CHOICES:

MECHANICAL

Installing higher-specification valve seats/valves plus, usually. It is best carried out in conjunction with a planned decoke or engine rebuild. Some engines are easier to tackle than others, but very few are impossible. It is essential that the work is carried out diligently - poorly fitted valve seat inserts can come loose and wreak havoc within precious old engines...

ADDITIVES

The additives used (usually sodium or potassium based) do not afford as good protection as lead, but are better than nothing. It will be the same octane as premium so retarding the ignition will not be necessary. Oft-the-shelf additives are unlikely to be better: chemists worldwide have been trying for 20 years to find an effective alternative to lead -they're unlikely to find one in the next 18 months.

DO NOTHING

Cars already driven on leaded have a "lead memory" that can last for 20,000 miles before valve seat recession has any effect. Cars with the softest valve seats can continue to run indefinitely without modification if driven gently. Ensure your cooling system is in perfect condition with the correct thermostat, re-route fuel lines to avoid vaporization. The vast majority of classic-car drivers will never need to do anything more.

LEAD: THE KEY INGREDIENT

Tetraethyl lead was first mixed in petrol in 1921 by Walter Midgeley Junior, who discovered lead "anti-knock" properties, enabling higher compression ratios to be used. Leaded fuel was first sold in 1923 as "Ethyl" by General Motors in the United-States, and the Ethyl Corporation was formed a year later. Ray Bevan (who died in 1997) set up a branch of the American Ethyl Gasoline Corporation in Britain in 1928, and since then leaded petrol has been available in the UK. It was soon discovered that lead also had a "cushioning"/lubricating effect between the exhaust valves and their seats. This enabled the seats and valve faces to last far longer- especially where the materials used where relatively soft. It has also been claimed that metering needles such as those in SU and Zenith-Stromberg carburetors, and the finer components of fuel-injection systems, may have a much shorter working life when running on unleaded.

Levels of lead in petrol have dropped drastically in recent years, from approximately 0.8 grams per litre in the 1970s, to typically 0.15 grams today Shell's 'low lead' four star (still leaded, to BS4040) contains only around half this level, but is said by the company to provide full protection against valve seat recession.Valveless (two stroke and rotary) power units should run on unleaded, as will vehicles manufactured from 1990 on, virtually all of which have catalytic converters fitted and must only use unleaded.

MARQUE-BY-MARQUE GUIDE

A-B-C-D-F-H-J-L-M-N-O-P-R-S-T-V-W

This is intended to be a guide (only) as to what may be the appropriate course for running your engine on Premium (95 RON) unleaded, based on best available current thinking. It is the result of extensive research, taking in as broad a cross-section of sources and views as possible.

ALFA ROMEO index

Pre-1965: Ideally fit hardened seats and higher specification valves.

Post 1965, inc Giulia, 105, 1600 Junior, Spiders, 1300/1600/1750/2000, 2000 GTV, Alfasud, 33, Sprint, Alfetta, Giulietta, (up to, but not including fuel-injected models - 75, 90, etc.): Usually necessary to retard ignition timing 3°.

GTV 6, 90: No modifications/adjustments required.

75: Ensure that correct relay is fitted in fuel-injection system for unleaded.

Alfetta Gold Cloverleaf, Bosch Motronic ignition: Very high compression use LRP or octane-booster or lower compression ratio.

ALVIS index

Pre-war: Fit higher spec seats/valves/guides. Some engines (e.g. 1930 Silver Eagle)'difficulty, due to insufficient depth of metal in head casting. Speed 25 modified head available from Owner Club.

Post-war: Fit higher specification seats/valves/guides; relatively easy.

AMERICAN CARS (GENERAL) index

Pre-1971/2 models: No rule of thumb; experiences vary even between examples of same model - some run well on unleaded, others require higher spec seat inserts, valves, guides.

1972 on: Virtually all were unleaded-compatible from new but beware of engine/ cylinder head swaps for earlier types.

ARMSTRONG SIDDELEY index

No "official" advice, but:

Pre-war models: Sidney Special Six has aluminium-bronze valve seats so may be OK; others use cast-iron seats so will eventually need hardened inserts.

Post-war 16hp, 18hp and Sapphire 236: Insufficient evidence to offer specific advice; use leaded as long as possible then LRP.

Star Sapphire, 234 and 346: Tests on newly rebuilt engines show recession after 2000 miles; hardened valve seats may be fitted but depth of metal behind seats is marginal. Fit new valve guides unless originals are perfect.

ASTON MARTIN index

All models: When running on unleaded after the suggested modifications, it is usually unnecessary to adjust ignition timing; only retard if detonation occurs.

DB2/4 Mklll (Engine no prefix DBA): Non-removable valve seats; machining difficult due to shallow depth of metal in head, but can be done, or suitably modified earlier head can be fitted. Mklll head prone to cracks/porosity.

DB4-DB6, Lagonda Rapide (3.7/4-Litre six cylinder engines): Fit higher specification valves and seats, plus new guides.

V8 models, two valves-per-cylinder versions: Fit higher specification valves and seats, plus new guides. Multi-valve engines already unleaded-compatible.

AUDI index

Pre-1976: Fit higher specification seats and valves, plus new guides.

1976 on: Unleaded-compatible. Injection-fed engines require ignition retardation. Later cars have knock sensors which 'recognize' octane rating.

AUSTIN/AUSTIN-HEALEY AND OTHER BMC/BL index

Pre-1989: Ideally fit higher specification seats/ valves and new guides.

BMW index

Pre-1985: Higher specification seats and valves, plus new guides recommended.

1985-on: M3, 535i, M535i, M5, 635 CSi, M635 CSi, 732i, 735i: Fit higher specification valves and seats, plus new guides. Other models are OK to run on unleaded.

BORGWARD index

All models OK on unleaded with no adjustments.

BRISTOL index

All 2-litre cars: Fit hardened valve seats, plus (usually) valves; adjust ignition timing as required.

V8 407/8/9/10 and some 411s: Fit hardened seats and valves, + new guides.

V8 411 Mark V 'J' engine: In theory OK on unleaded.

F-series: Fit higher specification seats and valves, plus new guides.

BUBBLE CARS index

Isetta, Heinkel, Trojan four strokes: Fit hardened seats and valves

CITROEN index

Pre-1985/6 models: Higher spec seats and valves, plus new guides recommended. Owners of some early cars (including Traction Avants and D-series) have reported satisfactory running without modifications, but no long-term proof. On early CX and GSA, experience shows that recommended modifications are necessary.

DAIMLER / LANCHESTER index

Conquest and other pre-1960s models: Fit higher specification seats and valves, plus new guides. Note: Some owners have run Conquests on unleaded without modification, but long-term effects are not yet fully evident.

2.5V8/SP250: Standard seats cope with unleaded, but higher spec valves may be required (e.g. stainless steel with chrome stems).

Sovereign/Double Six: Please see Jaguar entry.

DATSUN / NISSAN index

240Z and pre-1978 260Z, 300ZX Turbo: Fit higher specification seats and valves, plus new guides.

Late 1977/8 260Z, 280ZX and 1984-89 non-turbo 300ZX 31 models: OK.

FERRARI index

Ferrari advises: Older high-mileage, correctly maintained cars will have fully settled valve seats, so regression will not be a major factor. The factory can supply hardened valve seats or in certain cases, replacement cylinder heads already fitted with them. 348tb/ts, Mondial t, 328, Mondial 3.2, 308QV, 412 (with K-Jetronic), Testarossa, F40: OK but performance may suffer.

308, 2-valve Mondial, 288GT0, 365GT4BB, 512BB: Conditionally OK on unleaded but NOT for high-speed/track use.

FIAT index

X1/9,127,128: Retard ignition or use LRG. (45bhp, 903cc 127s,1971-84: OK).

Turbocharged Unos: Officially cars up to 1988 chassis no 07194809 are unsuitable for running on unleaded, with later cars OK. However, some enthusiasts maintain that these cars can use unleaded.

Strada 105TC,1982-85: Retard ignition or use LRG. Other classic models: Fit higher spec seats and valves, plus new guides.

FORD index

Sidevalve, pre-crossflow OHV, crossflow, Lotus Cortina, pre-1988 OHC Pinto, plus V6 Essex and Cologne engines: Experiences vary between individual engines; some appear to run OK without modifications, but others (including some examples of V6 2.8 and 3.0-litre units) suffer from rapid valve seat recession. For continuous running on unleaded, higher specification valve seats are recommended plus, usually valves (standard specification usually OK) and guides (which MUST be in perfect condition). Slight retardation of ignition may be required on higher compression models.

1988-90 Pinto: Engines have harder valve seats and may be OK without mods.

CVH engines to 1986: Can be fitted with later heads, which are fully unleaded-compatible.

Sierra Cosworth: Use LRP or try octane-booster.

HILLMAN, HUMBER, SINGER, SUNBEAM-TALBOT, SUNBEAM index

Higher specification seats and valves (typically stainless steel), plus new guides recommended. Some owners are running without modification, but mileages are not yet very high.

Hillman Imps are said by some to be OK on Premium unleaded, provided that ignition timing is retarded.

JAGUAR index

1930s/40s 1.5/2.5/3.5-litre and Mark V: Fit higher specification seats and valves, plus new guides.

XK twin cam and V12 engines, to 1980s: Despite relatively `hard' valve seats, erosion can occur although some individual engines are OK. Cars from 1968 were said to have harder seats-valves. If burning/erosion occurs, fit higher spec seats and valves, plus new guides.

Series III XJs, from 1981 /2 on: Valves suitable for running on unleaded but may need LRG or ignition retardation. For later 3.6-litre engines, if detonation occurs, fit 4-litre timing pick-up mounting bracket (it retards the timing). For early 3.6-litre engines, if any doubt about condition of head gasket, replace with a new factory item before running on unleaded.

JENSEN index

1950s/60s 541, C-V8 and Interceptors to 1974: Fit higher spec seats and valves, plus new guides. Ignition retardation by 2-3° may be needed.

JOWETT index

Pre-war sidevalves and Bradfords: Low-rewing engines tend to last well; may be OK but not yet proven long-term.

Flat fours: Hardened seat inserts recommended (some porting required to blend into head); standard valves OK, with cast-iron guides. Superior guides and valves available. Power loss can be compensated for by skimming heads, plus porting and balancing combustion chambers.

LAMBORGHINI index

Fit higher spec seats and valves, plus new guides; retard ignition timing.

LANCIA index

Note: Some engines (inc Aprilias and pre-war ones) appear to be more tolerant than later units, but so far mileages are relatively small.

All supercharged and turbocharged models: Theory dictates leaded only on, for example,1985-on Thema Turbo but specialists suggest from experience that these are OK.

1600 Fulvias: Exhaust valves attacked by lead, therefore run on unleaded!

All other Lancia engines: Fit higher spec seats/valves, and, ideally new guides.

LAND-ROVER index

Four and six-cylinder engines: Some owners report no problems on unleaded, even in hard use, though general consensus is that there is a high risk of valve seat erosion, so higher spec seats, valves and guides may be required.

Post-1985 4-cyl 2.5-litre units (17H engine no prefix): OK on unleaded.

V8: See Rover.

LEA-FRANCIS index

Pre-1980: Valve seat life shortened when running unmodified. Fit higher spec seats (can be difficult), plus valves, and new guides.

LOTUS index

Pre-1974: Fit higher spec seats/valves + new guides.

Most 1974 on: OK; high-compression engines require higher octane.

Esprit Turbo,1986 on: Should run OK without adjustment on Premium unleaded.

MASERATI index

Fit higher spec seats and valves, plus new guides; retard ignition timing..

MATRA index

All unmodified versions require valve seat protection; fit higher spec seats/ valves, plus new guides.

MERCEDES-BENZ index

Unleaded compatibility varies by age of vehicle and engine type/number Where engine has 'soft' valve seats, installing higher spec seat inserts enables running on unleaded (valves OK). Usually no ignition timing adjustment should be necessary; however, some cars have octane-adjuster plug/switch which can be re-set for unleaded running.

Pre-June 1981: 'Soft' valve seats; fit higher spec seats.

June 1981 to April 1985: Some models run OK on unleaded; others still require higher spec seats.

MG index

All pre-1989 models: Fit higher spec seats and valves, plus new guides.

MORGAN index

See entry under relevant engine manufacturer.

MORRIS index

All models: Fit higher specification seats and valves, plus new guides.

NSU index

Air cooled models: May be OK on unleaded, since valve seats comparatively hard. Experience over high mileages still being gained!

With the exception of early (especially twin-cylinder) models of the 1950s/60s, valves are stellite-tipped so only valve seat inserts might be needed. The standard guides (if in good condition) should be OK.

Rotary: OK on unleaded.

OPEL index

Pre-mid-1980s models including Senator A, Ascona B, Manta B, Rekord E and Commodore C: Except as below not suitable for continuous running on unleaded; fit higher spec seats and valves, plus new guides.

Manta B: 1.8S/GTJ,1982-88- OK on unleaded; no ignition adjustment required. 2.0 GTE, from engine number 20E-0355000 (March 1983) - OK on unleaded, but adjust ignition timing to 7° BTDC at 825rpm and disconnect vacuum pipe.

Monza : To engine number 30E-0077999: fit higher specification seats and valves, plus new guides. 3.0i/3.OGSE, from engine number 30E-0078000, March 1985 on: OK on unleaded, but adjust ignition timing to 7° BTDC at 800rpm (700rpm, auto versions) and disconnect vacuum pipe.

PEUGEOT index

Pre-mid-1980s models: Fit higher spec seats and valves, plus new guides.

205 GTI and CTI 1.6, XU5J (180A) engine,1984-86: Retard ignition timing by 2°.

205 GTI 1.6, XU5JA (B6D) engine,1986-9, pre catalytic converter: Retard ignition timing by 3°.

205 and 309 GTi 1.9, XU9JA engine,1986 on, pre-catalytic converter: Use high-octane unleaded, or try an octane booster.

PORSCHE index

Note: Non-catalyst models only listed.

356, 912, 914/6, 914/4 with engine types W or AN, 911 all models to 1984 and all 911 SC, 924 pre-1979 and Turbo and Carrera GT: Fit higher specification valve seats and valves, and new guides.

924 1980 on, 928/928S 1980-86, 944 engine types 44/01 and 44/03 1982-85, 911 Turbo, 1984 on, 911 Carrera, 1985 on: Use high-octane unleaded.

944, engine types 44/05 and 44/06, approx Feb 1985 to 1987: Use highoctane unleaded or adjust engine control unit.

914/4 engine type GB, 9281978-79, 928S4 1987 on, 924S 1986-88, 9445/S2 and Turbos 1987 on, 944 1988 on, 911 Carrera 4 1989 on: OK on unleaded.

RELIANT index

All Reliant's own units (including early sidevalves) to 1989/90: Fit higher spec seats and valves, plus new guides.

Ford units: See Ford.

SS1- Rover K-series engines and Nissan 1.8 Turbo: OK on unleaded.

RENAULT index

Pre-mid-1980s models: Fit new valve seats and valves, plus new guides.

Alpine GTA, non-turbo, 1986-89: OK on unleaded; reset ignition timing to 11° BTDC at 850rpm, vacuum pipe disconnected.

RILEY index

Riley 9,12/4,12/6,14/6, 15/6,1920s/mid-1930s: OK on unleaded, though on any fuel these engines tend to bum exhaust valves every 10,000-15,000 miles. Can be difficult to fit valve seat inserts; serious risk of breaking through into water jacket if machining-out seats. Heads also prone to hairline cracks. Higher spec valves can be installed for longer life in hard-worked engines.

Post-war RM models: Fit higher specification valve seats and valves, plus new guides. Coolant temperature critical.

ROLLS-ROYCE / BENTLEY index

All models except 1984-89 Bentley Turbo R: Should run happily without modification on Premium unleaded.

1984-89 Turbo R: Use high-octane unleaded.

ROVER index

P2, P3 and earlier engines: Fit higher-spec seats and valves (stainless), plus new bronze guides.

P4, P5, P6: Fit higher specification valve seats and valves; standard guides OK.

V8: Advice varies; some say fit higher specification valve seats and valves, plus new guides, but some long established specialists have found that Rover V8s do not readily bum valves/seats on unleaded. Early cars (P58, P6) have very high compression ratio; needs to be lowered: fit lower compression pistons/large valve SD1 cylinder heads.

SAAB index

V4/99: Fit higher-specification valve seats and valves, plus new guides.

All Turbos have hardened seats, but pre-1983 cars do not have Saab's APC system, which automatically retards the ignition system if the engine starts to pink, so use high-octane unleaded.

Turbo models from 1983 with APC: OK on unleaded.

Other pre-1985 model year Saabs: Fit higher specification valve seats and valves, plus new guides, or fit cylinder head from equivalent later Saab.

1985 model year and later Saabs: OK on unleaded.

SKODA index

Estelle, Rapid and earlier models with cast-iron cylinder heads: Fit hardened valve seat inserts/ valves. Check cylinder head valve guide drillings are in good condition: if badly worn, fit valves with oversize stems, or a better cylinder head.

136 Rapid: Early cars (up to G/H registration - can vary) need modifications or a later type head. To establish whether engine is unleaded compatible, check as follows: White-painted badge near No 1 spark plug plus undrilled boss near No 4 plug, or blue badge near No 1 plug plus drilled boss near No 4 plug: designed for leaded fuel. Green badge near No 1 plug, plus undrilled boss near No 4: later Favorit-type head, OK on unleaded.

STANDARD index

Fit higher spec valve seats/ valves, plus new guides.

SUNBEAM / SUNBEAM-TALBOT index

See Hillman entry

TOYOTA index

All engines OK on unleaded except:12R (1970s Hi-Ace van),18R (Celica 1978-82 and Cressida). Ignition retardation required on Celica/ Supra (except 2.OGT 198589 and 3.0,198ü89), also on 2.8-litre Crown,1980-84.

TRIUMPH index

The 'official' advice is that all Triumphs except the Acclaim require higher specification valve seats, valves and new guides. Upgraded fuel-injection equipment is also available for PI engines. That said, owners have been running Heralds, Vitesses and 2.5PI models for several years in hard use, with no apparent problems so far.

Acclaim: OK on unleaded.

TVR index

Grantura, Griffith, Tuscan, Vixen, 1300, 2500/3000M, Taimar, 3000S: Fit higher spec valve seats and valves, plus new guides.

Most models mid-1980s on: OK on unleaded, but depends on chassis and engine number.

VANDEN PLAS index

4-Litre R: OK on unleaded.

Other models: Fit higher specification valve seats and valves, plus new valve guides.

VAUXHALL index

All pre-mid-1980s models: Fit higher specification valve seats and valves, plus new valve guides.

VOLKSWAGEN index

Air-cooled: Fit hardened seats, higher spec (stainless) valves and new guides.

Golf GTI / Scirocco GTI 8-valve models: OK on unleaded; retard ignition timing on cars with engine codes EG (1.6,1976-82), EV (1.8,1984-87), DX (1982-89).

Golf GTI / Scirocco GTI 16-valve models: Use high-octane unleaded.

VOLVO index

All B18 and earlier engines: Fit higher spec valve seats, new standard spec exhaust valves and new valve guides.

B20: Most - as B18, but USA-spec B2OF engines OK on unleaded.

B21 E,1975-82: OK to run on unleaded.

B23E / B230E,1982 on: OK on high octane unleaded; for Premium, fit two head gaskets plus deeper water pump seal.

Six-cylinder B27E, B28E: Use high-octane unleaded.

262 Coupe, B28A engine, 1980-81: Not recommended for running on unleaded. Fit higher specification valve seats and valves, plus new guides.

WOLSELEY index

See Austin entry