What about rRestored car motors and unleaded gas?

I'm really wanting to buy a car from the 30s or 40s. I have owned a number of them in the past, but it was long ago. But, I'm wondering what is done about using unleaded gas in these old engines? Nobody seems to mention this.

Heavily leaded gas is a post WW2 thing. Many cars with engines designed prior to WW2 were designed for no or low lead and much lower octane gas than you can get today. For example Chrysler built cars in the 1930s had hardened exhaust valve seat inserts. In some cases those designs were kept through to the end of the 1950s. Even without exhaust valve seat inserts your issues with lack of lead are under high power, high temperature operation where you are near incipient ping. With 87 octane (or even 85 octane if you are in some of the western mountain states) your low compression pre-WW2 engine designed for octane ratings in the 50s, 60s or 70s should never get close to pinging unless you have it wildly off of factory tune. And you aren't like to to be towing heavy loads in the desert heat with them.

Throwing lead additive into those cars only helps the bottom line of the snake oil salesmen who sold you the stuff, does nothing for the car and is harmful to your pocketbook.

So basically leave worrying about lack of lead to the people with '60s muscle car engines who may actually have something to worry about.

Ply 33 is quite correct. If you want to, you can add some Marvel Mystery Oil, Redex, Bardahl or other upper cylinder lube to the gas but it really isn't necessary.

The cars that suffer from lack of lead, are those from 1954 or 1955, up through 1970 especially the high compression, high performance models. Earlier cars were made for low lead or no lead, low octane gas and of course, all cars from 1971 up are built to run on unleaded.

Lead was not added to gasoline until 1937 or so I believe. Amoco Premium NEVER had lead.

It is also throwing poison into the air that affects the brains of developing organisms including humans. It is an affront to the future to use lead additives, especially when not needed.

Worldwide, leaded gas was introduced at different times and removed from the market at different times. This "natural experiment" allows some interesting studies to be done. It appears there is a correlation between change in use of leaded gasoline in an area and an 18 year or so later change in the rate of violent crime in that same area. Given the known effects of lead as a neurotoxin, it seems plausible that the correlation is the result of a cause and effect relationship.

However I find that many people reject health or environmental arguments against the use of leaded gas so I just focused on the person's financial bottom line which is often a more compelling argument.

Thanks for all of the interesting replies. I guess it won't be a big issue with a 48 Plymouth flathead 6.

Thanks for all of the interesting replies. I guess it won't be a big issue with a 48 Plymouth flathead 6.

With that car you might want to check out the forum at http://www.p15-d24.com/

Thanks for all of the interesting replies. I guess it won't be a big issue with a 48 Plymouth flathead 6.

All Chrysler engines up to the mid fifties came from the factory with hardened exhaust valve seat inserts and hardened valves. The valve mechanisms are durable. If you are looking at one to buy, suggest you do a compression test or have your mechanic do one. These engines are foolers, unlike engines of inferior makes, they will continue to run quiet and smooth when in an advanced state of wear. The only symptoms are hard starting, low power, increased fuel consumption and sometimes oil burning. Many times, people have thought their old car was just naturally slow when in fact, it was worn out and due for a rebuilt engine. Once they rebuilt the engine, they were impressed with how much power they had.

If you have good oil pressure and good compression, the engine is good. Oil pressure should be 40PSI @ 30 MPH. 10 - 15 at idle. "Perfect" compression 110 -120 PSI depending on model and compression ratio. 90 or more is enough to go along with, as long as all cylinders are within 10 pounds. Lower than that, there is an overhaul or rebuild in the future.

This is nothing to be scared of, the flathead six is one of the simplest and easiest engines to rebuild and all parts are available at reasonable cost.

As I recall, the addition of "lead" was a means of octane enhancement, not specifically an anti-wear additive (for the valves). It allowed the "compression race" to advance into the "horsepower race".

Although AMOCO gas was not in the area I grew up in (in TX), it had high-octane unleaded fuel at a time when compression ratios were high and such. In magazine articles on that subject, NOTHING was mentioned about issues with their gasoline causing valve issues.

On the other hand, I found an SAE magazine article which reprinted a Chrysler "paper" on valve seat recession, from 1973 (when Chrysler recommended one tank in every three tanks be with a gasoline with lead in it). In a proving ground test, a '73 Town&Country station wagon (440 V-8) with the HD trailer package hooked to a travel trailer . . . with the eventual "max weight" for towing/hauling was reached. Under 70mph speeds, high load, higher engine heat conditions, within 12K miles the exhaust seats were non-repairable (due to valve seat recession) on heads without induction-hardened exhaust valve seat areas (not direct inserts in that area). QUITE a bit more intense of a driving condition than almost any older can will ever endure (in the future).

Enjoy!

NTX5467

Leaded gas was introduced in about 1928. At first the amount of lead was small and the leaded gas was about 55 octane. Unleaded about 50 octane.

As methods of refining gas improved, octane improved. The cracking process made it possible to turn low grade petroleum products into higher grade gasoline. By the late 30s 60 octane regular and 70 octane high test were the rule.

In 1954 or 55, oil companies introduced high octane fuels of 90 and higher. By the sixties, 85 octane regular and 95 octane hi test were the rule. Some companies offered even higher octane fuels like Blue Sunoco 103 octane. Other companies offered 100 octane fuels.

These fuels all contained large amounts of lead, much larger than had been used before 1954. This heavily leaded high octane fuel continued to be made until 1970 when unleaded was phased in.

So, 1955 - 1969 cars may be at risk with today's unleaded, especially high performance models with high compression engines, over 9.5:1.

The rule is your octane should look like your compression ratio. A Model T with 4.5:1 compression will run on 45 octane gas, the next thing to kerosene. In fact some owners of cars from the teens and twenties mix 10% to 25% kerosene with their gas.

Today's 87 octane regular for cars up to 8.7:1 compression and 92 octane for above 9:1.

Naturally this is not an exact rule, just a guide. Generally speaking, new engines need less octane in proportion to their compression ratio, so a car with 10:1 may run happily on 92 octane. While the old engines need a little more octane.

I should also point out that old, long stroke engines and old engines generally wore their engines faster than new cars, especially the piston rings, cylinders and valves. If the unleaded gas is too dry, you can add a little upper cylinder lube like Marvel Mystery Oil, Redex, Bardahl etc to protect the engine and prolong its life.

Good information, Rusty. One thing, though, is that what's "posted octane" on the pump is NOT the Research Octane number that was used before octane ratings were posted on the gas pumps, as it is today.

In the "low lead Seventies", the base "regular" fuel went to about 91 Research Octane from its prior 95 Research Octane levels, due to the decrease in the lead additive content. This later became the "87 Pump Octane" rating we now have. Mid-grade was 93 Research Octane, with Premium grade being 97-100 Research Octane. Mid-grade became the current "89 Pump Octane" and Premium started out at "91 Pump Octane". As refining processes evolved, premium is now typically "93 Pump Octane", depending upon at which altitude the filling station might be at.

The highest "Pump Octane" I've seen was in the '72-'74 time frame, in Lubbock TX, at the Phillips 66 station I bought gas from back then. Their premium "Flite-Fuel" had a pump sticker of "95.5 Pump Octane". If the averaging of "Motor Octane" and "Research Octane" was what it was, that would have meant that particular fuel was at 101 Research Octane. I know the '66 Chrysler Newport I was driving ran better on it, even with the 2bbl 383 (regular fuel) V-8.

In the '57 time frame, premium fuel was usually at 97 Research Octane. I feel the current premium unleaded fuel (at 93 Pump Octane) basically equates that Research Octane level.

The reason that higher compression ratios are now "doable", compared to the earlier times of the pre-unleaded decade, has to do with things other than just the mechanical compression ratio of the engine. First, modern engines have many electronics on them to retard spark advance if "clatter" happens, allowing higher compression ratios for better highway fuel economy and retarded spark for higher-load detonation resistance. Plus other engine design factors, like the current model Corvettes, including combustion chamber design and how it interacts with the piston crown height and design. It's the total engine management computer software that allows these "60s-era compression ratio levels, compliance with emissions standards, AND the ability to use common "pump gas" (even if it's the higher octane variations) . . . as a part of a total package situation.

In the realm of piston rings, I haven't heard of any issues regarding unleaded fuels causing more wear. I suspect that would be more the result of what kind of rings were used, whether the softer cast iron rings or the harder chrome-plated rings. Not to forget the "quick-seater" rings which some mechanics liked to use in earlier times. Or the fact that engine machining operations have better evolved since the earlier times. Better control of grits and other finishing stones for the cylinder bores, plus, of course, better lubricants as things have evolved. NOT to forget the role which valve guides (and related wear therein) can have, too.

The use of additional fuel lubricants might be an advantage with modern fuels, too, to possibly decrease the effects of ethanol'd fuels in use today. A judgment call that an owner would need to make.

Although the earlier engines might need some specific "higher maintenance requirements" compared to engines designed/built in the '70s and later, what each one might require can be specific to that particular engine family. Learning of these "kinks and whinks" can be important in making them work as good as they can.

Just some thoughts,

NTX5467

Adding/commenting on NTX5467's comment. . .

Octane is measured using a couple of different test cycles using a specially built test engine. There might be other test cycles but two are “research” and “motor”. For a given fuel the research octane number (RON) is usually higher than the “motor octane number” (MON). The number on the pump in the United States is the average of the two test results (RON + MON)/2. That is not necessarily true in other countries (I think there are some that use the RON number on the pump).

In addition to better spark control some modern engines can get by with lower octane fuel in high compression engines by actually changing the valve timing.

Is it true that "modern" piston rings exert very little pressure on the cylinder walls compared to the old cast iron rings? That would be one factor in there being less wear these days.

Cleaner burning would account for some reduced wear in "modern" engines too. The oil becomes contaminated less quickly and loses its lubricating properties less quickly than times of old, not to mention the huge improvements in oil and its filtering.

It is true, modern low tension rings wear the cylinders less. Old engines would wear faster no matter what kind of gas they got. I suggest upper cylinder lube in the interest of longer engine life but it is not strictly necessary.

I suppose the other thing is that now they use fewer and far thinner rings. You only need a knife edge to seal - look at modern oil seals with two and three knife edges or "lips".