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Higher temperatures CAN increase the likelyhood of knock, as can a great many other factors: increased compression ratio, advanced ignition timing, spark plug heat range, the exact shape of the combustion chamber and everything in it (including valves and the plug), carbon build-up, reduced cooling, increased load.
Knock is essentially the one thing that limits a spark-ignition engine in making power. If it weren't for knock, all spark ignition engines would have compression ratios in the 17-20:1 ratio, and there'd be little difference between spark ignition and compression ignition engines (Diesels) in efficiency. 150bhp/liter specific power would be commonplace instead of limited to bike and full race engines.
Any spark-ignition engine is designed to run on a particular octane. In poor countries, most cars have low compression ratios (below 8:1 is common), as typical pump gas there is quite poor, in the 75-85 octane range. Octane in rich countries is limited primarily by economics, as well. The technology is available to make even unleaded gas with 100 octane or more, but it costs more. The 91-93 available in the US is now considered the happy medium between price and efficiency. Once fuel efficiency really becomes a concern again, engines will start to be designed to require higher octane fuels to improve that efficiency, and there will be pressure to increase octane at the pumps. However, the fact that hybrids exist shows there is enormous resistance to increasing octane, since just doing that (and increasing CR) would substantially increase fuel efficiency and reduce SOME emissions (HC and CO, but NOx would rise).
In the early 1970s, gas typically had higher octane that we have today. Even cars with points-fired ignitions and carbs had 10:1 compression ratios in 1968, when the Type 4 was first appearing. Throughout most of the 70s and 80s, CR dropped as just doing that lowered emissions, and engine temps rose due to increased load from air pumps and EGR valves. Octane fell, too, partly because of the removal of lead (an octane booster), partly because it wasn't needed anymore. By the 90s, when computer controls matured, CR rose again, but octane did not. Indeed, in California, premium has fallen in octane over the past few years. Such are the politics and economics of oil. Thus, more and more newer cars require premium gas, whereas in 1980 almost no new car required more than about 85 octane.
This is why '73 and '74 914s have lower octane requirements than the '70-'71 models, and the '75-'76 models are lower still.
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