Unleaded Fuel and TVRs

This FAQ describes how the impending demise of four star and super unleaded fuel will affect your TVR. In most cases, this is not a problem at all. In others, it is and may require the use of additives or, in the longer term, cylinder head conversion. All the books discuss the impact of unleaded in detail. For more information, either click here to access the sample chapter PDF file on ignition systems for more information on fuel grades, ignition timing and other useful information.

The fuels...

LRP, Super Unleaded and Leaded petrol

The demise of 4 star at the beginning of 2000 has seen the introduction of LRP or lead replacement petrol which has effectively replaced 4 star on the forecourts. Unfortunately, there is no standard for this fuel yet and although it seems that all the manufacturers are using a potassium based chemistry, the proprotions and details vary. Some are even saying that they are not suitable for cars that tow trailers or cruise on motorways for long periods! Turbocharged cars seem to be particularly susceptible to problems, it seems.

LRP is essentially Super Unleaded fuel that has been doctored with an additive. As a result, it should not be used with additional additives as they may react and cause problems. It is better and cheaper to start with regular unleaded and add the additive to that. Note that the Octane level of Super Unleaded is now 97 and not 98 as it used to be. It has come down in price and is only a few pence more than regular unleaded. Some garages are even selling it at the same price as LRP.

The concensus is that if you use LRP then the prudent thing is to stick with one manufacturer to prevent different additives from causing problems. Although all the major suppliers are using potassium based additives which should be compatible with each other, there are is no standard to ensure this! It is being worked on but the safest thing is to play safe.

OptiMax

This is a new replacement fuel for Super Unleaded sold by Shell. It has a slightly higher octane rating of 98 compared to 97 RON of current Super Unleaded. It should be viewed as a slightly better quality Super Unleaded fuel and wherever Super Unleaded is used, Optimax can be used with no engine changes what so ever. Some owners claim better running but this is something I and others haven't noticed. If its suits your car then use it.

So which fuel do you choose?

If the car is fitted with a catalytic converter, do not use LRP! You should only use Super Unleaded (or OptimMAX) or regular unleaded. With Super Unleaded or OptiMAX, you should not need to do anything! With regular unleaded, you may need to make some adjustments to cope with the lower octane or use an octane booster suitable for cat-equipped cars.

If the car does not need leaded fuel to protect the valve seats and does not have a cat, then you can use anything virtually providing the car does not pink. The choices are:

• Regular unleaded and adjust the timing if necessary.

• Super unleaded or OptiMAX and no adjustments.

• LRP and no adjustments.

• Regular unleaded with an additive.

If your car needs leaded because of valve seat problems, then the choice is to use LRP or regular unleaded with a fuel additive. If you use LRP, then stay with one recognised supplier and not necessarily your local supermarket who buys in fuel from wherever and whoever has the best deal. This means the LRP chemistry may vary from day to day or week to week. Until there is a standard, you cannot be quite sure what you are getting.

Many of the classic car magazines are recommending the use of regular unleaded with a proved and tested additive until such times that there is a LRP standard.

Which additive?

This is a list of additives that have been approved by the Federation of Bristish Historic Vehicle Clubs and is from Practical Classics magazine. There are many additives and magic cures that claim to work but don't! Note the different chemistries and it is adviseable as a result, to select a type and stay with it. If you want to use a similar chemistry to that used in LRP (currently all Potassium based), then use a Potassium based additive.

The cars...

This section goes through the cars and identifies what action (if any) you need to take.

Cerbera 4.2, 4.5, Speed Six engined cars

These cars are fitted with catalytic converters and due to their more sophisticated ECU, can run quite happily on both unleaded and super unleaded fuels. Later cars may have a switch that changes the ECU mapping to get the best from each fuel.

Griffith 500, Griffith 4.x, Chimaera, V8S, V8 Wedges

All Rover V8 engines were fitted with hardened valve seats and therefore the only problem with running unleaded is the lower octane that unleaded fuel provides. This can cause pinking and predetonation which can cause engine damage if ignored. This can be cured in most cases by simply having the ignition adjusted. The less performant engines are less susceptible to pinking and thus it is common for the 4 litre engines to often require no adjustment at all. This is certainly not the case for the 5 litre cars and the more exotic Wedges. In all cases, Super Unleaded can be used with no modification but it was extremely expensive compared to standard unleaded. With the recent duty changes, it has come done in price!

Remember, if the car has a cat, don't run LRP or use a cat unfriendly additive.

There may be some power loss but really, this is so insignificant that most people don't notice it if it does happen.

Ford V6 (2.8 engined cars) e.g Tasmin, 280i, S1

Ford started to use hardened valve seats around 1983 but unfortunately some engines with the unleaded unfriendly cylinder heads have appeared to have got through. Add to that the fact that some cars may have add older replacement engines fitted and the position is not clear.

The S series cars should be OK and fitted with the D/E stamped hardened cylinder heads.

The later Tasmins and 280i cars should be fine as well but the only way of confirming this is to look at the cylinder head code. These may be run continuously on unleaded fuel, providing they have been fitted with the later version cylinder heads with hardened valve seats. These can be identified by looking for the letters D or E that are stamped on the cylinder head exhaust flange upper face. Note: it is easy to confuse this with the TVR engine number and code which are located on one of the 4 upper flange faces and may also contain a letter D. The engine number is typically below the engine code, which also causes some confusion. The TVR engine number should contain the letters WPP and, from 1985, also has the letter D added. The engine code should start with PR (standing for 2.8 litre fuel injection). If there is no letter, assume that the cylinder head does not have hardened valve seats and will need a tank of leaded fuel or an additive as per the earlier cars.

Replacement heads are available but as the car is a V6, you will need two heads! Many of the Classic car magazines will advertise companies that can convert the cars.

Ford 2.9 V6 e,g S2, S3, S4

This cars are already unleaded friendly and the only thing that you may need to do is to adjust a plug on the ECU. A Ford/TVR specialist can help here.

Tasmin 200, M series and earlier cars

These engines do not have hardened valve seats and will either require conversion or the use of additives.

Can I use unleaded in an emergency?

Yes but don't labour the engine. This will help prevent pinking.

Do I need to panic?

It depends. There is an lead memory effect that will help protect the valve seats if unleaded fuel is used. This does mean that any valve seat recession will occur over hundreds and thousands of miles and not instantly! The chances of having thousands of engines die as soon as unleaded is put in is a bit of an exaggeration. In the long term, cylinder head conversion is the best solution especially if car does a lot of miles. In the short term, fuel additives will protect the engine. Some owners are taking the view that the cylinder heads will need replacing through normal wear and tear anyway and will wait until this is required, and then fit unleaded cylinders.