I guess I should have stated “what gas”. Many suggested a small amount of MMO to lube the valve guides.
High altitude air is thinner and has less oxygen meaning it is less dense and there are fewer oxygen molecules to fire the combustion process. An engine sucks in air. The amount of fuel it can burn is limited by how much air it can suck in.
The higher the altitude above sea level, the lower the octane requirement of the fuel. This can be explained by lower atmospheric pressure at high altitudes. While the static compression ratio of a given engine remains the same, the pressure developed during compression is lower at higher altitude.
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High octane fuel is not needed to drive around in slow motion, even with high compression (8.6:1) cylinder heads.
Note: None of this is dealing with emissions in anyway…
You don’t get into high compression octane until you hit the 9.5:1 with iron heads and 10.5:1 with aluminum heads on modern (V8) engines, my fun car has 9.5:1 with iron heads and I have to run 93 octane or greatly retard the ignition timing with a big loss in power… If I went to 10.5:1 with the same heads I would have to run a race type gas like 101 octane or an octane booster…
You can start out with a higher then needed octane (just to be safe) to tune the engine for power, and the best ignition timing curve, and then lower the octane until you start to get spark knock, then go up one octane and that is the best octane for a performance engine… So ignition timing is not affected by higher octane, but lower octane affects ignition timing due to spark knock… Meaning, run the lowest octane you can with out spark knock on the engine, as long as you or the computer is not having to retard the ignition timing to stop any spark knock that will give you the best power and fuel economy…
Modern cars advance the igniting timing until the knock sensors pick up any detonation/preignition/spark knock and then retard the ignition timing until it is gone, so running a higher or lower octane in your 100% computer controlled stock vehicle will change the ignition timing and affect your fuel mileage and performance, always run what the stock vehicle calls for…
Now with these newer all aluminum engines being able to dissipate heat better with the cooling systems and inject the fuel in the cylinders better they are capable of running much higher cylinder pressures and compression ratios with 91/93 octane fuels, it is a whole new ball game…
And that Mazda Skyactiv X 16:1 or what ever compression-ignition is just crazy… lol
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As long as we’re talking flat head Fords, I came across this aftermarket head for a Model T. DOHC, 16 valve, and made be the Chevrolet brothers after Louis left the car company:
Yep, we explained that to him, but some people still insisted on 93.
Correct me if I’m wrong but seems to me most current oils still have some zinc in them, just not the same percentage as in the past?
You are correct, all motor oils have some Zinc, the American Petroleum Institute’s rating caused the industry to systematically reduce levels of zinc in their oil since 1994…
So like a tire with 15 psi of air in it on a vehicle that requires 30+ psi, it will still roll ok down the road, but it is not enough to keep from damaging the tire and being unsafe for cornering and braking hard… Modern oil does not have nearly enough Zinc to properly protect flat tappet (lifters) camshafts and lifters… But once everything went to roller cams & lifters, there is no need for the normal amount of Zinc from like the 60’s/70’s (and however long it was in oil, I do not claim in anyway to be an oil expert)…
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Brothers? Chevrolet was the name of the French Race car driver Durant went in partners with after he was fired as Chairman of GM. He named the company Chevrolet. Then after just a year Durant bought out Chevrolet. Then GM bought Chevrolet putting Durant back on the board of GM.
Yes, Arthur and Louis Chevrolet. Another brother, Gaston, died driving one of their Frontenac race cars.
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But it was only Louis who went into business with Durant. And he was Swiss…Not French like I said.
Per wiki:
" Louis Chevrolet (1878–1941), Arthur Chevrolet (1884–1946) and ousted General Motors founder William C. Durant (1861–1947) started the company on November 3, 1911[3] as the Chevrolet Motor Car Company."
Edit - but it looks like you’re right, the article on Arthur states
" In 1916, the year after Louis left the Chevrolet car company that he had co-founded, Arthur Chevrolet assisted Louis and Gaston in the new Frontenac Motor Corporation."
I corrected the earlier entry.
And, just to add a note of automotive trivia to the discussion, Ford has owned the Frontenac name for many decades. They used it for the Canadian version of the Falcon.
You’re correct, my error. Lead for the valve seats and Zinc for the tappets.
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The Chevrolet brothers were noted engineers and manufacturers of race car equipment before branching out into automobile manufacturing, at some point thereafter Billy Durant bought the company and took back control of GM. Unfortunately he never shed his bad habits, the GM bankers ousted him again, and he wound up his life managing a bowling alley in Flint Michigan.
Most of their race car, performance parts, and aircraft engine work was after the Chevrolet/GM stuff.
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It’s been 50 years but I recall Durant in management studies. I guess you don’t have to remember who but what.
Hugher altitudes have lower air pressure. Lower air pressure multiplied by the same compression ratio gives less effective pressure in the cylinder, lowering octane requirements.
Yes, the old system of measuring octane gave higher numbers. High test pump gas in the 50s ran up to 102 for Golden Esso. I used Amoco high test in my 56 Desoto hemi and it was lead free and rated at 101 octane. I could advance the timing 4 degrees with it and It prevented lead fouling of spark plugs.
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Speaking of car maintenance back in “The Good Old Days”, this postcard was sent to Studebaker owners by a Stude dealer in the '50s.
Yeah well I got a notice to bring my vacuum cleaner in for a cleaning and inspection. So some are still doing it.