Unleaded fuel in older cars

A friend of mine, Jaime Kitman, who owns at presant count, 19 1960's era cars, noticed 12 years after giving up on trying to keep up with adding lead additives to non-leaded gasoline that he had no engine failures. He decided to do some investigative jounalism. It became the whole issue of the Nation Magazine one month. It started like this:

"The next time you pull the family barge in for a fill-up, check it out: The gas pumps read "Unleaded." You might reasonably suppose this is because naturally occurring lead has been thoughtfully removed from the gasoline. But you would be wrong. There is no lead in gasoline unless somebody puts it there. And, a little more than seventy-five years ago, some of America's leading corporations--General Motors, Du Pont and Standard Oil of New Jersey (known nowadays as Exxon)--were that somebody. They got together and put lead, a known poison, into gasoline, for profit."

The rest is here:

http://www.mindfully.org/Pesticide/Lead-History.htm

He is writing a book on the subject at this point. I am sure, like the synthetic oil conversation, there is lots of "empirical" evidence one way or other. There are probably some myths that ARE true and some that are just myths.

That is why there is the internet so that hundreds (or thousands) of us can get into these types of discussions as opposed to two or three people at a time as before.

Yale

 

On older cars I have owned including a 330GTC I would use 93 octane unleaded and add a little Marvel's Mystery oil and a lead additive to help out. I never had any engine problems over 25k miles or so.

 

If that is the same Kitman that writes for Automobile Magazine, he is the resident leftist, not that there is anything wrong with that.

 

Should you not use a low octane in these cars (assuming no knock)?

 

That's ok, 'cause the steering wheel is over there, anyway.

 

I run Sunoco 93 or 94 octane in my Dino. Occasionally, I drop a tank of 100 octane in there for fun.

I haven't noticed a difference in performance from the 93 to the 100, and it's never knocked, despite the 10:1 compression ratio. I have hardened seats in the engine.

I do add a little mystery oil, but no lead addititves.

 

The lead in fuel is tetraethyl lead. Not lead on its own. It was Thomas Midgley in the 20's who discovered that it improved the octane rating of his fuel. Harry Ricardo saw other improvements in his engines, he realised that it not only increased the octane number but also reduced wear on the valves/seats compared to other octane improvers. This latter is the important point today.

If you buy unleaded with the same octane number as leaded it will have exactly the same anti knock properties. The only worry for old car owners over unleaded is the wear on the valve seats. When the valves and seats get very hot there is a localised welding effect . When the valve moves away again it takes a tiny piece of material away with it. TEL prevented this.

The chances are that these cars are rarely used today under engine speed/load conditions that will lead to excessive valve damage unless they are regularly tracked or generally thrashed every day. But I still put lead substitute in the tanks of my old cars purely as a precaution. My Healey for instance has notoriously poor cylinder head cooling so I don't take the chance. I also change the oil and other fluids more often than I should.

Cheers
Simon

 

The question of octane number and engine power is another one that keeps coming up. 93 octane and 100 octane have exactly the same energy in the fuel. The difference is in the way you can get as much of that energy out as possible. That is done by igniting at the best point during the engine cycle.

An engine has an optimum ignition timing to give maximum power. When you set up the ignition timing you try to be as close to this point as possible. If you increase the compression ratio of you engine or use too low octane fuel then you can't reach this optimum timing. It is limited by the onset of knock. The vehicle manufacturer recommends a fuel with an octane number with which this optimum timing can be reached.

Straight off, with older cars you will see no gains with high octane fuel unless you also reset ignition timing. If you run a carb car and you set the ignition timing with 89 octane in the tank you will see no improvement with 100 octane. If you set the timing with 100 and then add 89 the engine will knock.

Modern cars automatically adjust ignition with the ECU so in theory can reap the benefits of higher octane. However, if the manufacturer says you can reach best ignition timing with 93 then you don't need 100.

Back to my little old Austin Healey 100M. The compression ratio has been upped to a whopping 8.8 so the car is set up for 100 octane. It needs this higher rated fuel for me to be able to set the ignition to achieve the maximum performance. If I used 98 I would always be seting the distributor to just before the engine knocks when 2 or 3 degrees earlier would have give me more power.

Cheers
Simon

 

Ah yes the misinformation continues. Simon just look at the research Kitman did. Lead in gasoline was about making money not about what was better for your car (or need I say it, ourselves). The Europeans, later to the lead free thing, have held onto their leaded beliefs with more vigor then us stateside. I am sure leaded gas is not the only reason, but do you remember when engines in cars were done for at 50 - 60,000 miles? Best, Yale

 

Gumout and Marvel's Mystery Oil in the gas.

Don't use anything else.

Only have 2200 miles on the engine since the rebuild, so I'm probably not the best indicator of wear and tear for this discussion.

And, I don't know spit about oil or additives. I just do what the guy who is smarter than me (the factory trained Ferrari mechanic in this instance) tells me to do.

 

Has anyone had any luck with a product called "Lead Supreme-130"

 

I never understood, when you have pinging or pre-ignition, this is when the fuel/air mixture ignites too soon, then you have to RETARD the ignition timing, how is that? If the mixture already ignited by itself, the spark was too late already, retarding the ignition makes it worse not better???????

 

The fuel air mixture in the cylinder does not burn all in one go as many people think. It is a steady process. The flame progresses through the mixture with the spark at the centre. The pre-ignition refers to auto-ignition of the unburnt gas ahead of the flame. The phrase pre-igniton then, does not refer to pre spark plug but pre normal ignition, normal being when the flame arrives at that point in the cylinder.

As the flame advances it heats up and compresses the unburnt gas ahead of it. The earlier the spark the more time this gas has to reach the critical conditions to self ignite.

This auto-ignition sets up additional pressure waves inside the cylinder. Depending on engine operating conditions, speed/load, these pressure peaks can be so large as to cause material damage inside the combustion chamber.

If you are auto igniting before the spark discharge....then you have real problems my friend

Cheers
Simon

 

Sounds a little too much like conspiracy theory for my taste.
Yes TEL in fuel did give lead at the tail pipe, which is poisonous, which is why it was banned, which is a good thing. Everything that comes out of your tail pipe is poisonous.

My entire professional career has been in engine combustion. So I know the mountains of research that have been done on these subjects.

Yes we call this progress. What a certain german company described as "Vorsprung durch Technik". Material technology, control technology, production techniques, lubrication, combustion, our knowledge of these things improves daily. The engines of tomorrow will last even longer.

Cheers
Simon

 

Rob, you are right about knock, self ignition and the similarities with a diesel.
The difference is that (simply put) in a diesel, it self ignites but we are adding fuel at a steady rate controlling the combustion. In a spark ignition engine all the fuel is already in the chamber nicely mixed with air, so when that ignites the rate of energy release is much higher than the diesel...and thats the bad bit.

Just as a note of interest. Our ability to precisely control combustion within the combustion chamber has increased massively in recent years. Within the next few years we will see engines in cars where "good" knock/ping is used to optimise the combustion process.

As a driver you will see no difference, but from a technical view point very interesting. But it will be a nightmare for the chip tunners

Cheers
Simon

 

My 1972 Lotus has replacement hardened valve seats and so uses unleaded gas. I never add anything as I don't think I have to. Brand name gas has all the cleaners you need and also has a Winter/Summer formula. 93 octane is plenty for street use.

Lotus said my timing should be 5 degrees static advance (actually under 1000 RPMs) but this was to pass emissions. We all set ours between 10-12 degrees. This gives a LOT more power with our 9.5 or 10.5 Comp. ratio cars.

The limiting factor for advance in my car isn't knock (the Lotus twin cam hemi design is rather knock resistant due to the swirl pattern of the mixture), but starting the thing! Too much advance creates back pressure (?) in the cylinder and you'd think the starter was bad. Retarding a couple degrees from that point and all is well.

The sacrifice for all this advance is a less than perfect idle, so I upped it from the factory 950 RPM's to 1200. It likes that much better.

Ken