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Leaded vs. Unleaded in Model A's


HeyPop
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A recent post (Old time fuels) spurned a few question that maybe some of the newer Model A owners may want answered. The one on my mind is the use of lead additives in unleaded gas. I've been told you need to use non-detergent oil because of the lead bearings and leaded gas because of the valves. I'll buy the non-detergent oil but what about the use of lead additives? Is it really necessary? I have a friend who swears he needs it in his tractor or it will be ruined. After asking him why.. he said because his Dad said so.... His Dad was 90 when he passed. Can I tell him differently and feel secure in saying so? confused.gif

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I think you already got your answer from Pete Hartmann and Model A Hal in the thread about old time fuels. But being a verbose fellow, I will dive in.

Basically the octane rating of commercially available fuels of the late 1920s and early 1930s is not exactly known because the testing methodology that is now standard was not done then. But based on historical documentation it seems that the octane was in the mid 60s. Call it 65 octane. That limited the compression ratio available to engine manufactures of the era. For example the "high compression" head available for Plymouth in 1933 was 6:1. You typical car in 1930 probably had a compression ratio of 4.5:1.

Unless you have significantly modified the compression ratio of your engine, your octane requirement is still about 65. As was noted in the other thread, running a higher octane rated fuel does no harm. So you are safe running 85 or 87 octane fuel in your car. There is absolutely no need to use the mid or higher octane rated fuels.

As for leaded fuel: The reason lead was added was to increase octane. I personally feel that the supposed advantage of cushioning valve seats was a minor thing compared to the issues created by lead and the lead scavengers in the fuel destroying exhaust systems, fouling plugs and contaminating the oil. Notice that engine life for new cars is much longer than on the old cars? 100K miles on a tune up? A lot of that is better components, but at least some of it is because of unleaded gas.

Getting back to valve seat recession: As Pete noted in the other thread, this basically happens when the engine is run at high speeds under high power and temperature conditions. We typically don't drive our 70 year old cars that way. And even if we did, there is a mitigating factor: The reasons why high power and high temperatures are bad is because you are running into the regime of incipient pre-ignition. Since modern fuels have a much higher octane rating than the fuel of 1930, it is much harder to get pre-ignition to occur in your old car. If you have your mixture and spark advance properly adjusted you should not be able to get into a incipient pre-ignition regime no matter how high the load on the engine nor the ambient temperature.

Leave the gas additives to those poor folk who have the 1960s muscle cars with the high compression engines. They may actually need that stuff. Those of us driving pre-WW2 cars have nothing to worry about in that regard...

As to Pete's other point about stabilizers. I have also heard from a number of reliable sources that the additive packages in modern fuel have a short shelf life. The number I hear most often is 6 months. For those of us who take more than 6 months to finish a tank of gas (think winter storage here), we have a problem. There are additives to help with that. (My solution is to drive the car occasionally year round, but then it does not snow where I live.)

Another issue is that some of the additives in modern fuel are not kind to the types of rubber found in older cars. Your model A should not be too much of a problem as it has no fuel pump or rubber fuel hose. But it may have a rubber tip on the float valve. Just keep an eye out for problems in that area and be prepared to replace the damaged parts with new ones that are made with modern materials.

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Tod :

On ONE point of your discussion above ( damn...do I love it when people agree with me.. ! ) I must DISagree. That is your comment on engine life. Yes, having "cleaner burning" fuels is a significant factor. However, there are thee other areas that I think are far more significant.

1) INDUCTION AIR FILTERING - engines are air pumps. They pump in FOURTEEN gallons of air for every gallon of fuel burned ! Go try and find a neighborhood auto repair shop that still does cylinder re-boring. Yes, it is still done, but at a much lower frequency than prior to World War Two. That is because the wear from abrasive air has just about been eliminated. In heavy trucks that get regular service and are run more continuously than we typically run passenger cars , even under high loads they operate under, engine life of 300-600,000 miles is the NORM !

Up until the early 1930's, cars didnt even have air filters ! The old "oil bath" filters that started showing up in the mid to late 1930s were better than nothing, and did increase engine life, but are NOWHERE near as good at getting the finer abrasive particles out, as the modern "paper" style filters.

2) OIL FILTERS.....higher quality engines started having FULL FLOW oil filteration in the early 1930s ( both my '38 Packard V-12 and my '36 American La France V-12 came stock with built in full flow oil filtering and cooling). Yet we didnt start seeing full flow oil filtes on consumer-grade autos, until the 1960's. That alone doubled or tripled ....or MORE....engine service life.

3) VASTLY SUPERIOR OILS. Gawd...does it ever want to make me puke when I hear people call em "detergent" oils. That unfortunate term was originally coined in the 1950's, by the advertising agencies hired by the oil companies to explain the new technology oils. THERE IS NO SUCH THING AS "DETERGENT OIL" !

What we DO have now, in the modern "approved type multi season" oils, is oil that has additives that prevent "long chain" molocules from "linking up" with the dirt from the combustion processinto carbon particles which become sludge (as noted in the previous discussion about FUELS, the combustion process from modern fuels is so much cleaner and easier on the engine anyway).

The two other tremendous advantages is "constant viscosity" oils (why in hell they call them "multi-grade"...is just another example of those "pretty boys with clean hands" in the auto advertising industry....trying to think up terms that an ignoramous can understand....! ). The new oils maintain a constant viscosity thru out the engine's operating range. At COLD temps, they stay thin enough to get oil up to the rings and valve guides FAST....whereas the old "single grade" oils would have viscosities that wandered all over the place dependant on temps. A typical "single grade non detergent" oil can be thick as molasses when your engine is cold....and if you get your engine hot, above the temp. the "single grade" oil was certified at, you are going to get oil SO thin you can have accelerated wear and even destruction.

The other big advantage of modern oils is they have "wear inhibitors" which dramatically decrease engine wear.

And yet...can you imagine.....there are still a few ignorant clowns around who love to say..." I will only use non-detergent single grade oil".......gawd....!

Pete Hartmann

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I knew it would stir more thoughts and responses by moving the thread to it's own spot. OK... good to know I can use leaded 87 octane fuel from Sheetz and pick up some KK's while I'm there. Am I still on the right track with the oil? Detergent / non-detergent... what ever... will they in fact distroy the mains in my A? confused.gif

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Hi Hey Pop!

In answer to your question, you cannot buy a modern "off the shelf" motor oil that fails to meet the current SAE ASTM specs. Therefore, the answer to your question is go ahead and use ANY "legit" multi grade oil you can find ANYWHERE in the United States, with confidence it will triple or quadruple the life of your engine....ANY internal combustion engine, over oils from the so-called "good old days" and/or so called "non detergent" oils (which dont have to meet ANY spec).

Let me give you a personal illustration of how silly it is to call these "non sludging" oils "detergents" oils.

When I bought my '38 Packard V-12 in 1955.....it had 100,000 miles on it and was barely running. The motor was so full of sludge when i got the valve "door" off, I couldn't even see the hydraulic lash "take up" mechanisms (Packard V-12's had a very sophisticated mechanism that MECHANICALLY took up valve lash thru a hydraulically activated system of off-set cams).

I overhauled the engine IN THE CAR, taking EVERYTHING out and cleaning it, except for the crank and cam. It took literally DAYS...was a horribly messy job. I was broke, so I couldn't afford a re-bore - just use cheapo soft iron rings...knowing I'd be lucky to get 50,000 miles out of em. It ran great for a while...but.....as you will see later on, I did have to eventually take the block out of the car and have it re bored.

But for fun, to show my buddies who stupid they were to argue with the then relatively new oil technology that is even more superior today, I deliberately left some sludge in two areas.....One...on a crank throw, and the second, on a ledge on the block casting just above the "lip" for the oil pan.

In the early 1970's, I took the engine down again, as the bad bore had eventually beaten up the rings.

The engine block and crank were as clean as when I had assembled it some 20 years earlier..BUT the "test sludge" areas...WHERE STILL THERE !

Back together again...and back on the road ( My Packard V-12 may well be the last of the big-engined classics still in service as a almost daily "beater").

Last year, I had to change the front timing case cover ( On Packard V-12's, this casting also carries the water pump and water passages - they corrode out over time). I also changed the radiator core. While I had the hood off and the engine accessible, I pulled off the valve door and oil pan to inspect everything. Sure enough....THE TWO SLUDGE TEST SPOTS ARE STILL THERE....NEARLY 90,000 MILES OF USE LATER, WITH SO CALLED " detergent " oils.

It is unfortuate that back yard "so called" "mechanics" often exhibit the human trait of being frightened of what they don't understand....and...because they did not do well in school, havnt even the foggiest notion of the basics of chemistry and physics. If you are seriously interested in fuel and oil issues, and how the technology evolved, I strongly recommend you go down to your public library's main branch, where they will probably have back-issues of the SAE JOURNAL ( this is the technical journal for the Society Of Automotive Engineers). The articles from the 1930's to the 1950's are especailly fascinating, as they show the evolution and connection between so many fantastic improvements that make modern cars so vastly superior to what we knew as kids.

Pete Hartmann

Pete Hartmann

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This has been a concern of mine for quite some time. When I took my 57 T-bird off the road for its restoration several years ago - she ran fine, burned no oil , etc. but had a debilitating sludge build-up in the oil pan - so much so that the oil was not being pumped properly onto the rocker arms. Took engine apart and cleaned it with kero several times to remove as much sludge as possible. Was told to run only "non-detergent" oil when I get back on road again because "detergent" oil would dislodge any sludge that I may have missed and potentially clog one of the oil ports or flow passages. Should I not be so concerned and run the modern oil? How about synthetic?

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since multi-grade "detergent" oils were in use (and, if I recall, by '57 were already REQUIRED to keep the new car warranty in effect) when your car was new...sounds like some back-yard mechanic must have been using cheapo oil in it - no way could ANY...I say again..ANY legit oil "sludge up" like that.

See my post above for my own personal "test" which establishes....there is NO SUCH THING AS DETERGENT OIL...gawd.....how many times do I have to explain the basics of oil chemistry....all these additives do is 1) reduce wear 2) stabilize viscosity and 3) PREVENT MORE sludge from forming.

The synthetics are even better than mineral oil - especially in their resistance to extreme temp. break-down. But you can't possibly get your oil temps high enough to need that benefit. Wont you settle for the approx. 300-600,000 mile service that commercial drivers get from their vehicles from conventional "approved" oils, given the regular oil and air filter changes they insist on, and less per-centage of their driving in "cold start stop and go traffic".... ?

Pete Hartmann

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Model A Hal noted that the ideal air/fuel ratio could not be 14:1 by volume. It is actually by weight. And I believe 14.7:1, as originally noted by Pete Hartman is correct. For fun I have made up a little Javascript calculator to compute road speed and MPG for a given engine RPM, rear end ratio, tire diameter, engine displacement and manifold vacuum. You can find the Speed and MPG calculator on my web site. (I tried to put the calculator within this post, but the preview shows that it does not work. I guess that the forum software is stripping out the script.)

I don't know how accurate the script really is, but the numbers it returns based on my car result in reasonable values.

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