Whatever happened to leaded gasoline? | Fuel Facts

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Back in the day, leaded fuel was as common as 15-cent hamburgers. Today, though, things are different. 

Why Lead in the First Place?

Tetraethyllead has been added to gasoline for nearly a century. “It’s a very cheap and effective octane booster,” explains Zachary Santner, technical specialist at Sunoco Race Fuels. Just 6 milliliters of tetraethyllead, less than 0.2 percent by volume, makes the difference between the 120- and 100-octane reference fuels used for octane testing, he continues.

Why Did Leaded Fuels Go Away?

To meet the emissions standards introduced in the 1970s, car manufacturers began installing catalytic converters. Lead oxide, a byproduct of combustion, leaves a residue inside catalytic converters, rendering them useless. Lead as a fuel additive quickly fell from favor.

What Happened Next?

Less lead in pump gas resulted in lower octane ratings. As a response, engines were detuned. Remember the glorious muscle cars of the ’60s and early ’70s? That all ended around 1973.

Why Is Lead Used Today in Race Fuels?

The science hasn’t changed: Lead remains an inexpensive, reliable, effective way to add octane to a fuel. Sunoco, for example, still relies on lead to boost octane above 105. These race-only leaded fuels can’t be used with oxygen sensors or catalytic converters, of course.

What About Alcohol?

Fuels containing a high percentage of alcohol–think methanol–will, like high-octane fuels, also fight knock. However, these fuels require increased fuel flow, which requires specialized equipment. Quick side note here: The lab tests done to determine a fuel’s octane rating can’t accurately score highly oxygenated fuels. “We developed this scale for measuring gasoline,” Santner explains, “and now we’re trying to use this scale to measure fuels that aren’t like gasoline–E85, for example. Finding consistent information on octane of highly oxygenated fuels is very difficult.”

Anything New on the Horizon?

Look for a new wave of unleaded, high-octane fuels. Santner says that Sunoco is about to add another high-octane unleaded formula called Evo 10 to its lineup. It’s 10 percent oxygen by weight and carries an octane rating of 105 (R+M)/2. 

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Coupefan Reader
8/3/22 12:09 p.m.

Why did leaded fuel go away and you didn't even touch on the largest issue, health of people?  A chem 101 student can tell you how toxic lead is.  And if you want to research an interesting and important historical-medical-social aspect of lead being removed from society, look at the bloody strong statistical correlation of the reduction in violent crimes pacing the reduction of lead in the environment.  It's unmistakable what the side effects were.  Only the Roman's use of lead pipes and the enduring bad decision making that the neurological effects created can possibly best our modern experiment in widespread lead use.  

03Panther UberDork
8/3/22 9:53 p.m.

In reply to Coupefan :

After reading your post on what was left out (and you are 100% correct, although I'm sure sonoco doesn't like talking about it) I tried to read whole article, see what else they missed! But my connection is too slow...

One thing that got misunderstood at the changeover time, that got wives tales started:

The lead in gasoline at the time, helped "work harden" the seat surface. So seats were simply cut into the cast head, in many cases. With the at the time important break in period, the seat would harden from use, and all was fine. Switch to unleaded afterwards and normal daily driving was still fine. But recut a stock seating area (remember, we are talking about not adding hardened inserts here), for a stock valve job most guys been doing all along, break it in on unleaded, and the valve could beat it way through the head in several K miles! Due to the seat never getting the chance to work harden. But unleaded took the blame for not "protecting" the valve. 

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