Unleaded Or Leaded That Is The Question

Just wanted to see if someone out there can tell me what is required to get my s4 webber headed elan to drink unleaded fuel have had conflicting info from replace all seats and bronze guides or replace exaust guides and seats are hard enough to cope "stainless steel valves? " etc just want honest advise .I am lucky that I have a local garage selling leaded petrol but for how much longer? looking for a long term fix do not want to be removing head because of exaust valve /guide problems later on many thanks for any help

Hi

Try TetraBoost if you don’t wish to lift the head.

This is Tetra Ethyl Lead (the real thing) so you can make 4 or 5 star if necessary.

If you don’t do a lot of miles it makes sense.

John

I live in the midwest USA, buy brand name gas, Shell, BP, Marathon, etc. I’ve owned a restored S1 Elan for about 6 years, a Stromberg +2 for 5 years and just sold an S4 with Webers. The only time I’ve bought leaded gas is when I put racing fuel in them the few times I"ve drag raced at the local British Car Day. I’ve never had a problem concerning valves etc. I use premium unleaded fuel and can cautiously boast of more than 15,000 trouble free miles.

Dave - Check the archives for a more thorough discussion - but this topic has been discussed several times before. The valve seats are hard, as they are inserts into the alloy head - unlike some old US cars that had valve seats that were just cut into the cast head. I’ve been running premium unleaded and things are fine. Don’t worry about it - regardless of local mechanic comments.
Paul Zimmerman
65 S2

Hi, as a follow up to this question. I have had it suggested that there is a big difference between old leaded benzol petrol of Elan era, Lead replacement of nowadays and of course super unleaded in the way they burn. Suggestions being longer stroke cars such as MGB using unleaded, have a problem as the fuel burns more quickly and has finsihed burn before the ideal time for exhaust cam opening with result of loss of power but excess heat.
Several people I know of here in Greece with older BMW’s that have worn out catalysts are going to lead replacement fuel and finding it gives greater progession and lask of back firing.
A friend a Shell in the UK was not able to comment much but did accept that some unleaded contain oxygenates which could burn quiker and also make mixture a bit leaner.
Does anyone have any ideas on this or some scientific evidence please?
Richard

I’ve got nothing to add on valve/seat recession but I would like to throw something else into the debate.
My Sprint and Europa both have BV 126bhp engines in standard trim without lead free conversions, the late Graham Arnold advised U.K. owners to use Optimax petrol and I normally use LRP (lead replacement petrol) with out any problems, I have tried Optimax and can feel NO difference as my engines are quite happy.
The Sunday Times (u.k.) recently did an article under the heading “The wonder fuels that dont deliver”
http://driving.timesonline.co.uk/article/0…1289720,00.html
which concludes that the use of Optimax is of little benifit if any !
I have long since thought the claim’s of some owners regarding the extra power they gain by useing Optimax has been more in their minds then in their engine.
Any thoughts and comments? and lets hear from the "silent majority for a change!
Brian.
p.s.
If the link does not work do a Google search on “the wonder fuels that dont deliver”

Brian,

Several years ago the FBHVC commissioned tests on Additives. All those that were proved in their tests to stop valve seat recession are listed on their website. Interesting was the fact that no major fuel company submitted their LRP petrol for tests. Worryingly you are categorically told not to mix additives with different base constituents eg Manganese, potassium, sodium, so if you fill up with LRP from different manufacturers you are probably doing this.

LRP is now not being sold by many petrol stations simply because of lack of demand. Anybody that really cares about their engine buys unleaded and adds an approved additive. Most Lotus people seem to side with Millers with the Octane booster as the twin cam was supposed to run on 5 star.

I’m lucky enough to be able to drive through the Peak District and buy ‘Proper’ Leaded 4 star from a Bayfield Thrust Garage. Have you checked the FBHVC website to see if one of these Petrol Stations is near you? Apparently this is nearly 5 star RON anyway. If I’m paying ?1 a litre I may aswell use the good stuff!

Regards, Andrew

Richard,

The Octane rating is basically a rating of how fast the fuel burns, so whether the old leaded and the new unleaded work the same can at least in part be determined by the octane rating.

This also shows why the lead replacement fuels and unleaded in the UK may not work as well as the old unleaded. The unleaded fuels seem to have a lower octane rating so with the timing set for the higher octane leaded the engine would have more knock.

My car actually looses power when I add 110 octane leaded racing fuel, since the timing is then wrong for the octane rating of the fuel. My car runs great on 93 octane (R+M/2) fuel which is around 98-100 octane the way the UK measures octane. If I changed the advance when I put the racing fuel in I could get the power back.

So yes the lead replacement fuels may make the BMW with the burnt out catalyst run better, but it it likely that it is because the catalyst was burnt out by the engine running wrong and the LRP is a better match to the timing/mixture the engine is running at.

On a TwinCam the main thing to do when switching away from leaded fuel is to tune the engine to the new fuel since their is no computer to do it for you. On the BMW with a catalyst the engine management system should do that for you.

Rob

Andrew,
I agree with what you are saying and I do buy my LRP from one sorce, there is a garage that sells leaded fuel not too far away although I have never used it (I was told by another Lotus owner who uses it that “it goes off very fast”) and I dont use my cars very much.
Coming back to Optimax, the point I was making was that it is not "the best thing since sliced bread " or what ever the fuel company would have us believe although some Lotus owners would like to think so.
I do believe Optimax had a very successful marketing campaign and this means big profits for the oil company :angry: …the bottom line.
Rgds Brian

A thought…
Avgas (Aviation fuel) is 5* Leaded as far as I am aware. It’s about ?1.00 a litre in the UK from a suitable airfield??

Avgas is typically 110 octane (R+M/2 method) and better than the old UK 5 star was. Also its production is very tightly controlled with regards contaminants ( such as water) and has a formulation to maintain a high stability on storage and long term high or low temperature exposure.

Great for a low use car or a high compression race car. Unfortunately no longer legal to use on the road in Australia and subject to tight selling controls if not put directly into an aircraft. I need a special passbook to be able to buy it for my Elan to use in historic racing.

Rohan

I wwould just drive it on unleaded. If the tappet clearances need adjusting more frequently than before or you lose compression - have the seats, valves changed - I suspect however you will not have a problem unless you “cruise” at 7000rpm all day.

I was a spectator at a Ferrari Challange race a few years ago at the Homestead Speedway, and I asked the factory racing fuel vendor there about the suitability of Aviation fuel (Avgas) on a Lotus in lieu of purpose-designed racing fuel. He told me that the Avgas has de-icers added, and that that might not be such a good thing in a car engine. I don’t know if that is a problem or not.

However, I live near the Florida Everglades, and there are certain conventional gas stations in the area that sell high-octane Avgas at the pump to airboat owners whose airboats run on aviation fuel because they use airplane engines for propulsion. It’s not unusual to see a few muscle cars on a Saturday morning lined up for a drink as well…

Gary
'71 Elan Sprint

i use castrol valvemaster plus .it is well known and tested.it is used by most in the classic car world.i use normal unleaded fuel and have no problems.it costs about 10 pounds english and teats about 200 litres.if you use an additive stick to the same one and dont mix them.its the cheapest and safest way and keeps the car original

Hi there,
I’ve seen a few of you referring to the possible use of AVGAS in your engines. Please don’t do this. I’ve seen engines that have been ruined in a very short time due to the use of this fuel. AVGAS has a different type of additive package and IT WILL turn your engine oil into sludge.

AVGAS has a different type of additive package and IT WILL turn your engine oil >into sludge.

I am a mechanical and chemical engineer with 30 years experience in petrochemical plant operation which has included manufacturing large volumes of gasoline . I have also used Avgas in my racing engines for over 15 years as does everyone else in Australia where they are still allowed to run leaded fuels.

In Australia at least and also elsewhere also I beleive there is no fundamental incompatability between Avgas and common car engine components and oils. Avgas is specially formulaed and tested to minimise these risks because the consequence of an engine failure due to poor fuel or fuel incmpatiability is so much more serious in an aircraft.

Any commnets on the lack of suitablitiy of Avgas is an urban myth or old wives tale as far as I am concerned. If you have data please send me the references as in all my work on gasoline I have never heard of this problem.

The most common reason for oil sludging is generally due to excessively low temperatures in the oil caused by multiple short trips not boiling the water out of the oil. Synthetic oils used with extended change intervals such as in modern BMW and Mercedes tend to form a mouse like sludge in these circumstances especially.

Rohan
Lots of avgas and no problems

Hi Rohan,
I respect your qualifications and business experience. The use of this fuel in racing engines would not cause the sludging that I mentioned in my previous message because most racers change the engine oil after each event.
I work in the engine development department of BMW and have seen several engines that have been written off due to sludgy oil because the owners had used aviation fuel from their local flying club. Notably a high percentage of these engines were returned fom Australia.
No hard feelings but I still strongly recommend that fellow Lotus Elan owners steer well clear of this fuel unless they are prepared to make very frequent oil changes.
We’ve drifted off course from the poor guy with high coolant consumption
John

Hi John

Interested to see you worked at BMW on this problem. Did you investigate engine usage patterns in these cars and other fuel sources used ?

I worked on this problem in Australia where the gasoline feedstock we made was being blamed for problems in BMW’s and Mercedes. It was a high octane feedstock with high olefinic components and Mobil had been over blending our feed stock in premium unleaded used by these cars as it was a cheap source of octane rating. Our feedstock was also used heavily in Avgas for the same reasons of its high octane rating.

The investigations I did could find no relationship to our feedstock in gasoline to engine oil sludging. However at the same time I suffered a cracked bore in my race engine that lead to high water levels in my synthetic mobil 1 engine oil. I experienced exactly the same sludging as observed in BMW’s and Mercedes. Synthetic oils behave very differently to normal oils under water contamination either due to leakage or lots of short trips in egines with long recommended change intervals. The sythetic oil does not form a milky emulsion like normal oils but stays relatively clean because a thick mouse like sludge forms in the bottom of the engine that contains the water. Once this is thick enough it gets sucked into the oil pickup and the engine is stuffed. I dont think this water contamination risk with synthetic oils has ever been properly understood by many people. This is why I dont beleive Avgas is a risk in a normal car engine. Have you ever done any experiments on water contamination in sythetic oil to see its impact?

I change my race engine synthetic oil every 12 months in my car not after every race and would have done up to 3000 racing miles between changes and suffered no problems on Avgas over many years.

Rohan

Hi,
my involvement at the time was as dev. engineer for lubrication systems. Another guy was responsible for the oils we use.
The multiuple cold start scenario is a well known factor for sludge forming. The engines that were returned to us from Australia had up to 6mm thick layer of black sludge on all of the stationary internal components. These engines had an original oil fill of synthetic oil. It was confirmed that aviation fuel had been used in the cars.
It is always very difficult to obtain reliable, honest vehicle usage information from customers who are trying to get a free or reduced cost replacement engine for their car.
Thanks for your interest but thats about as much as I can discuss on an open forum.
John

John

Dont know when you experienced the problems with your BMW engines. The work I did was about 5 to 6 years ago

Just before the problem I worked on there was a separate problem wih Avgas in Australia due to incorrect over addition of additives being done. This stuffed up a lot of aircraft engines at the time and grounded all the piston engined aircraft in Australia while they were all checked. It was a major embarrassment and cost to Mobil. It may have been this that also stuffed car engines using Avgas at the time. The sludged caused by this excess additive problem was black. The sludge caused by water in sythetic oil is a dark grey and is was what was being identified when our feedstock was being blamed.

Use of leaded Avgas or race fuel in road engines has been illegal for many years in Australia now so your customers were breaking the law putting it in their BMW’s anyhow. It can only be used in a limited number of historic competition classes on race tracks and now requires a special pemit to purchase unless you put it straight into a plane.

Rohan