Answer: This is a very simple question with a not-so-simple answer. The answer applies to virtually all classic cars made before the mid 1970s.
Beginning in 1975, all cars sold in the U.S. were equipped with catalytic converters. These devices reduce the pollution coming out of a vehicles tailpipe by igniting and re-burning exhaust gases as they leave the engine, converting these exhaust gases into simple carbon dioxide and water. So far, so good.
Well, maybe not.
The problem is that catalytic converters are not compatible with gasoline that contains lead, which at that time was all gasoline. So right about this time, the recently formed EPA set standards and deadlines for slowly phasing out the use of lead in gasoline. Vehicle manufacturers knew that lead had benefits to an internal combustion engine, such as reducing detonation. But more importantly, it acted as a lubricant, or coating, to protect valves and valve seats from burning and receding as a result of combustion temperatures. The manufacturers responded by installing hardened valves and valve seats, and VIOLA - problem solved.
But what about the gazillions of cars that were still on the road and needed lead? Not to worry. Leaded fuel would still be available alongside unleaded fuel for quite some time. Leaded fuel would not be completely phased out until all of these older cars had worn out, crashed, burned or otherwise passed on to car heaven. In theory this was a fine plan, but here we are some three or four decades later and there are still many older cars on the road that are now considered classics. And all of these cars were designed to run on leaded fuel, which has gone the way of the dinosaurs, from which coincidentally it was made. Karma?
Shortly after the last precious drop of leaded fuel was pumped, dire predictions began to abound as to how long the engines in our classic cars would last. A year? Ten years? 5,000 miles? 50,000 miles? Every expert had their own opinion. The only quantifiable difference in these opinions were whether things would be terribly dismal, or horribly dismal.
Now, decades later, we have the benefit of hindsight. And guess what? In most cases it’s no big deal. If you keep your engine in a good state of tune, and use your classic car for its intended purpose, it’s likely that you will never have a problem using unleaded fuel. If you regularly drive 120 MPH, through the desert, while towing an 8000 pound boat on a trailer, uphill, you might have a problem. In fact, I would venture that you probably will.
If you do feel that you will be subjecting your classic car to these extremes, you can have any competent machine shop install hardened valves and valve seats in the cylinder heads. In many cases they will have already been installed if your engine has been rebuilt.
So go ahead and buy that 66 VW Bug. Just remember — no towing 8000 pound boats through the desert.
Contact Steve: firstname.lastname@example.org