Yes: It was indeed, and continues to be, all a big con.
From the inestimable John Deakin’s must-read article:
Lead in the Hogwash http://www.avweb.com/news/pelican/182149-1.html:
First, a few of the OWTs...
Lead Myths
•Lead does NOT "cushion" or "lubricate" valves. There is nothing in the serious literature, and no known scientific data to support this notion. If you know of something, please write. I said DATA, not some mechanic or overhauler mouthing this decades-old gossip. Remember, EVERYONE once "knew" the world was flat (and some still believe it). I do have one report that high-output marine engines had some valve problems when switched from mogas to unleaded fuels, but that same report said that hardened valve seats took care of that problem.
•Lead has no effect on the BTUs or "power" in the fuel. "Octane rating" has very little effect on BTUs or "power," and what effect it has is in the wrong direction. The more the fuel components are processed to raise the octane, the less "power" the fuel will produce. But the effect is almost negligible. The same "power" is generated by a gallon of 80/87, 91/96, 100LL, or the old 115/145, with or without lead. (What DOES change is the required timing for different fuels. Hold that thought. Timing is that all-important measure of when the spark lights off in relation to top-dead-center piston position.)
•Lead does NOT cause valves to run cooler or hotter. Lead does NOT prevent (or cause) "valve recession."
•Finally, EGT has little or no effect on valve temperature. Most of the heat comes from the very high combustion temperatures during the combustion event, 3,000 degrees Fahrenheit or more, and most of that heat is transferred to the cylinder, and the cooling fins. EGT shows the temperature of exhaust gas after the exhaust valve opens, by which time a great deal of the heat has been dissipated.
I know of NO known reliable DATA to support any of these notions, other than the well-meaning folks who happen to believe them, having heard them repeated over and over for decades. As I mentioned, there is some good data that refutes them, if you'll look.
Just for one example, the FAA ran a twin with flat sixes for several hundred hours, one engine running 100LL, and the other side with unleaded fuel. Then they tore both engines down and used some custom-built instrumentation to measure the valve wear. The lead did no good, at all. That's pretty good data, but I'd like to see more of it. Well done, FAA!
If any of you have scientific evidence for any of these, PLEASE point it out. I am NOT talking about "My mechanic says," or "everyone knows," I'm talking about published, scientific data by reputable people, who know what they're talking about.
At this point, let me point out that in the 30s and 40s, all the best and the brightest engineers were working with recips, and virtually everything we know about them comes from that era. Those people were ENGINEERS in the classic mold, and knew their stuff. What they did with primitive tools is astounding, and just about everything we're re-learning today was known then! Starting in the 50s, all the "best and brightest" gravitated to turbines, and it wasn't long before the general attitude was, "recips are dead." The old knowledge and "corporate memory" died, the marketing folks took over at Lycoming and Continental, and today we see the results. There may be a few real engineers left, but I don't see much evidence of that at the factories. The result is that most technical information coming from "the big two" is either intellectually dishonest, or solidly based on pure ignorance. There is NO curiosity left, and warranties are often worthless. The basic engines are usually excellent, having been originally designed by the engineers of yesteryear, but what the factories have done to them is pathetic.
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If lead doesn't add power, what does it do? Like "octane," lead ALLOWS a higher power SETTING without detonation. The primary means of accomplishing this is in simply reducing the speed of combustion. By reducing the speed of the flame front, it takes longer to reach maximum pressure, and thus that max pressure occurs later, after top dead center. Can you spell T-I-M-I-N-G, again? …
