Unleaded gas was required for all US made cars and trucks beginning in 1972, I believe, that is when GM changed, I don't know about Ford and Chrysler, they might have lasted another year. I had a 72 Chevy Monte Carlo with a 454 cu in engine. The compression ratio was 8.0:1, down from about 10.5:1 for the previous year. In other words the high compression engines disappeared and really did not return until a few years ago when they began to let the automobile computers decide what octane the owner was using, the computer takes care of the detonation. The usual regular gas these days ranges from about 85-89 octane, depending mostly on the altitude where you buy it. Locally 87 octane at 2800 ft. The manufacturers raised some vehicles back to about 9:1 compression a few years later, they required a middle grade of unleaded, I would guess about 90 octane in W Kansas. I had a 93 Grand Cherokee that was supposed to run on 87, it pinged so I had to use 90. To sum, the most used gas is regular unleaded, I would guess that the R+M/2 is about the same as it was in 1971, not sure about the 50's and 60's, but I don't believe the octane of regular has changed much. I do not believe there is any premium currently available that has as high an octane as some of the premiums available in the 50's and 60's. Whether you need 90-93 octane in an IH 6 cyl engine with 7.2:1 compression, I don't think so. I consider the cutoff to be about 8:1 compression, but you can certainly get if you modify the engine. I have a 460 that doesn't get used under heavy load, I use 87, regardless of what the experts say.
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Today's Featured Article - Experimental Tractors Article - by Danny Bowes (Dsl). Tractor technology appears to have nearly hit it's pinnacle of development. If you agreed with the subtitle, you are rather mistaken. Quite, actually. As a matter of fact, some of the technology experimented with over 40 years ago makes today's tractor technology seem absolutely stale by comparison. Experimentation, from the most complex assembly to the most simple and mundane component, is as an integral a part of any farm tractor's development
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