The lowering of combustion temperature was needed to reduce the production of Nox. The secondary effect was that it also reduced the tendency to ping under load. Some engines neede it others didn't.
I had a customer that brought in his car for a tune up and he complained about it pinging when he accelerated. During the tune up I found a ball bearing in the hose to the EGR valve. After removing it the ping went away. A few days later he returned saying the pinging had come back. Sure enough he had plugged the EGR line with another ball bearing.
Some people just can't leave things alone. If it's emission control it must be bad. Unplug the electrical connections to the computer controlled carburetor, Disable or remove any form of air injection, disable vacuum advance, remove heated air intake to the air cleaner, unplug knock sensor and on and on.
In the begining attempts to reduce smog was geared to reducing hydrocarbons only. It was only after several years of running extemely lean mixtures that it was discovered that they were actually making smog worse as the leaness was actually increasing the Nox in the atmoshere and that it was responsible for the yellow air over cities. It was around 1986 that everone got a handle on all the emissions coming out the tail pipe.
