Morgans and Unleaded Fuel


This article is a beginning of amalgam of articles and experiences with older Morgans and newer unleaded fuels. It will grow as data is accumulated. Is there a danger of running your Morgan car on unleaded fuel? For many models there is no danger at all,  however to others, there is a real danger of damaging your engine.

Lead has a lubricating  property, when you remove the lead friction is greater, thus  increasing the temperature. Abnormally high temperatures in  the combustion chamber cause valves and seats to erode. When running on unleaded exhaust valves and seats are  exposed to higher temperatures for longer, so any measures  that lower the temperature are worthwhile. Keeping the cooling system in good condition is one obvious measure,  you could also raise the final drive ratio helping to lower the  revs. Even on engines that are the most vulnerable running them below 3,000rpm will cause very little seat recession.


Don`t believe that all cars over 20 years old require thousands of dollars to convert them to unleaded fuel. Many cars need no conversion. If your car must be converted then calculate $200-300 for a four cylinder, overhead valve unit. If you have a complex V8 then it could cost you upto $5000 but the necessity for this is highly unlikely.

If work is required, plan it in conjunction with an engine rebuild. It is essential that the work is done diligently, poor work can wreck a precious old engine.


Gasoline-powered motors work by igniting a mixture of air and fuel at carefully timed intervals with a spark plug in each cylinder. Prior to each combustion, this air-fuel mixture is compressed, allowing its maximum energy potential to be extracted.  Use a balloon as an analogy. The greater you compress the air within a balloon the more powerful will be the explosion when it bursts. But in the case of an air-fuel mixture because greater compression creates greater heat, a fuel must be able to withstand extreme temperatures, otherwise it misfires prematurely. This issue, where the air-fuel mixture combusts spontaneously instead of from the spark plug, is known as “knocking,” named after the sound it produces. 

An octane rating is simply a measure of how heat resistant a fuel is in order to prevent knocking. In other words, octane doesn’t, per se, enhance combustion — but it does prevent the air-fuel mixture inside an engine from igniting before the highest possible compression point is reached and sparked by the ignition system. The higher the compression point, the more power the engine will produce. Additionally, the resultant combustion will be a more complete one, keeping the internals of the engine cleaner and lasting much longer. I have opened many Morgan Plus 8 engines and engines that have been fed higher octane petrol that are significantly cleaner compared to caked filth inside engines that used lower octane fuels. The US propane variants are amazing as propane has a VERY high octane rating, often 114 (aka 121 outside North America). Bt the way, different parts of the world use different Octane Rating systems and fuel quality varies greatly from nation to nation and most importantly WITHIN a country. BEWARE.

Of course, modern cars don't last and are not kept very long..making the longevity of their engines moot. Regular automobiles are A-B transportation and extra horsepower and longevity are unimportant. But Morgans are a hobby, not transportation, and should, if one is wise, be treated differently. One should not buy and maintain a car costing 10s of 1000s in a fashion that prejudices its performance and lifetime. Doesn't make sense!  Yet so many owners try to save money by treating their Morgan badly in this area.

POST THE ERA OF FULL ENGINE MANAGEMENT. There is, however, not much to do with later cars. Beginning in the mid-1990s, governments and manufacturers further reduced the ability of owners to easily adjust how their engines function by adopting computerized ignition systems, which rely on knock sensors and automatically adjust their spark timing to fit the fuel being used and the compression that can withstand. Owners can neither adjust the ignition timing nor the fuel maps. When they buy cheaper, lower octane fuel, the engine responds by producing lower performance and the resultant dirtier internals. Few owners know or even notice this as the cars, in honesty, are not really used as sports cars.

MORGANS MADE PRIOR TO THE ERA OF FULL ENGINE MANAGEMENT  Depending on your fueling/engine system, your fueling and ignition may be fully adjustable. For example, all Plus 8s prior to the GEMS management system can be adjusted by the owner. And systems prior to the Hotwire (1991-1999 for stock or 1996 in the USA) can also adjust fueling with the L-Jet Flapper and the carbs before. Plus 4s are the same. A precise adjustment of timing and fueling to the octane level of the fuel being used, remarkably changes the perormance and fun of the cars. 

WATCHPOINT: My Morgan lives  close to a famous racing Circuit. So when at home I can use Canadian 96 Octane (aka 102 Octane in the UK or Europe) in my Morgan Plus 8 (modified to 4.8litres). I have adjusted my timing (distributor) to that quality and marked it (with a white pen) accordingly. However, when I used to travel extensively in the US, I also marked a retarded timing that could run on the poorer US fuel quality. In Europe, I swapped in a miltary version of the 4.6 Rover V8 that can run on the very poor fuel quality one finds in the French,  Italian and eastern Europe backroads we adore so much. This provided me much more torque and no fuel hassles. In Europe, top speed is not a reasonable goal outside Germany. The only other alternative is to buy fuel only on Autoroutes and Autostrada.  In rural Canada one has to make an advance appointment and arrangements to find a speed trap or speed camera. ;)

You can consult me at webmaster at on what modern petrol and timing to use. The recommendations in your Owners Handbook are very conservative, as they are taken from the manufacturer's' recommendation for the sedans and 4x4 trucks Morgan engines are normally installed in. Happily, in the past, the units were fuel mapped and timed specially for Morgans and TVRS but sadly that did not change the Factory's suggestions.


Morgans are our hobby and an expensive one in terms of the car's value, now and for the future. Yet the less knowedgeable owners and their forums now fret about how much money they are spending for fuel and adopt unwise paractices more emaningful for mundane automobiling. But  manufacturers now cater to unwise owners with their modern fare. Beginning in the 1990s, fueling systems adopted knock sensors and computer managed engines which advance or more often retard ignition timing to reflect the fuel quality they feed their cars. Tests show that, in mundanemobiles, performance is only negligibly prejudiced by these systems and engine life is no longer important as the engine will normally last longer than the rest of any modern vehicle. 

Adjusting the timing

Many engines with average compression ratios (below 9.5:1) will run on 95 octane unleaded without problems with pinking. There can be great differences between identical power units, some are quite happy, others pink badly.

Try running the engine with its standard four-star timing, if pinking occurs try running using an octane booster.

If you still want to use unleaded and pinking is a problem try retarding the ignition by 1deg at a time, until pinking disappears. On EFI units,  then the ECU chip may need reprogramming or replacement. Retardation of the ignition timing has the undesirable effect of making the engine run hotter, also the engine can run-on, especialy high compression engines designed originaly for `five-star` fuel.

On older engines designed to run on very low octane fuels it can be benificial to advance the timing, again make adjustments in 1 degree increments, ensuring that pinking does not occur and the engine runs smoothly. By retarding the ignition this can reduce the running temperature of the engine, reducing the risk of valve and seat damage.


There are a number of products on the market that claim to enable trouble free running on unleaded, often with other claims of better fuel consumption etc. They also claim that the engine runs at a lower temperature thus helping the life of the engine. However, be skeptical about their effectiveness and how they work in practice. The testimonials quoted have no scientific basis and sometime are on cars that would happily run on unleaded fuel anyway. Independent tests have found them wanting..quoting octane enhancements in tenths of a percebnt rather than full percentages. READ THE LABELS!

The Mechanical Solution

On some cars only a complete engineering solution will do, installing hardened valve seats, higher specification valves and valve guides. The cylinder head or block in the case of sidevale units, needs to be in sound condition, with no cracks and sufficient depth of metal around critical areas around valve seats.

Aluminium cylinder heads are not automatically unleaded compatible, with materials varying between apparently identical power units. Birco, manufacturer of valve seat inserts for the British Motor industry, confirms that all inserts that it has made since the Second World War are technically hard enough to tolerate unleaded petrol, though modern inserts are considerably harder.

Opinions vary over the best route to take with valve guides. Most advise replacing the guides for both inlet and exhaust, although in the case of valves and seats only the hotter running exhaust items need to be replaced. The experience with phospher bronze guides is that the have a limited life of as little as 10,000 to 15,000 miles.

To find out what you need to do to your car see the models below.  


Sidevalve, pre-crossflow OHV, crossflow engines.  Experiences vary between individual engines; some appear to run without modifications, but others suffer from rapid 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: 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.


The `official` advice is that all Triumphs require higher-spec 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.

Rover V8

Advice varies; some say fit higher-spec valve seats and valves, plus new guides, but some long established specialists have found that Rover V8s do not readily burn 

valves/seats on unleaded.  Feedback would be appreciated.


There is nothing that will sap power and performance more than a poor camshaft and lifters. The distributer, the carbs or the ECU may be the "brains" of the motor and the crankshaft its muscle but the camshaft is its heart and the lifters (cam followers) its arteries. If they are not in perfect or near perfect condition, good steady performance impossible. 

Here is a picture of worn lifters or cam followers. Anything except a very slight depolish of the contact  surfaces is unacceptable. These lifters shown are NOT acceptable.  Above right:  The cam still looks good  but.......

Below right:  Look at those  lobes. The  arrow indicates the edge  where the follower rode on.  Even a SINGLE damaged lobe  like this makes a cam fit for  the scrap bin and not your car. On the good side, cam swaps on  a Plus 8 is not difficult, merely taking a bit of care, It is an engine in situ job, merely requiring the removal of the heads, the lifters (always change your lifters when changing your cam!) and re-shimming them. Of course, the motor oil most of these engines' owners in the last 20 years has made fast cam wear a sad tradition in this community. Ask if you want me to coach you through it.