ORIGINAL: 69mach1377

73 needs some 3.25 gears more than anything...or even 3.50s to wake up his car.

ORIGINAL: Soaring

After reading several long articles on this, it appears that it is agreed by several authors on this subject, that 1971 was the first year that all cars were required to burn un-leaded gas. I would assume then, that the 1971 on engines all had hardened seats.

ORIGINAL: Soaring

You guys are mixing apples and oranges regarding European built cars and U.S. built cars. Remember, the Europeans didn't have the EPA breathing down their neck as did the Yankees, and that happend in the late 60's. Here is a blurb from one of the articles I was talking about.
Tetra-ethyl Lead
Early engines had a lot of problems with loss of compression due to rapid valve wear. the valve surface just didn't last very long. In 1935, the Ethyl corporation started marketing a fuel additive to gasoline refiners which made the valve surfaces last much longer. It was known as "tetra-ethyl lead", or just plain "lead". It also increased the octane rating of the fuel. What it did was coat the surface of the exhaust valve with lead. This acted as a high temperature lubricant, slowing down the transfer of molecular sized particles from the face to the seat. The way it worked, was it coated everything that got really hot, with lead. It also coated the piston, combustion chamber, spark plug, and exhaust system, with lead. This lead powder was an abrasive, so it caused the rings to wear prematurely. It was also caustic, so it caused the spark plugs, and exhaust systems to wear out prematurely. Lead powder also got in the oil, contaminating it prematurely, requiring more frequent oil changes. In short, the lead helped the valves last longer, at the expense of the rest of the engine. It also meant gasoline refiners didn't have to refine their product as precisely, they just had to add lead to it.
It became apparent, by scientific research during the 1960's, that lead was also an environmental hazard. It got into the atmosphere from car exhaust, was absorbed by the clouds, and therefore the rain had lead content. The lead contaminated rain fell on the grass which absorbed it. The cows ate the grass, and we drank the milk the cows produced. Tests on humans revealed an alarming level of lead poisoning, and it was causing learning disabilities, and birth defects. Something had to be done! Every lifeform on earth was being contaminated by car exhaust. The newly formed Environmental Protection Agency (EPA) in the United States, started putting pressure on the car manufacturers to build engines that didn't require leaded fuel, and in 1971 cars built in North America, no longer needed lead in their gasoline.
As of 1975, most north American cars came equipped with catalytic converters in their exhaust systems. Catalytic converters convert carbon monoxide and unburned hydrocarbons, two pollutants in the exhaust stream, to carbon dioxide, and water. They do this by passing the exhaust gas through pellets, or a ceramic honeycomb, of platinum and palladium which is glowing red hot. Because lead coats everything that gets hot, it coats the catalyst too. The converter is useless after one tankful of leaded gas. If the car is equipped with an oxygen sensor, it too becomes useless after one use of leaded gas.