Almost everyone that owns "older cars" nowadays are worried about getting gasoline that will burn well in their particular car. The lead content is almost gone (it is gone in California) and the octane ratings seem to slip each trip to the pump.
Corvair owners are very fortunate in the respect that Corvairs do not need leaded gasoline. Corvairs are one of the very few cars built prior to the mid-70's already engineered for no-lead gas! Of course that was essentially by accident - the "extreme high operating temperatures (for the time) present in an air-cooled engine forced the Chevrolet engineers to use hardened valve seats and stellite faced valves. So that solves the lack of lead. (If you are still uncomfortable about this let me tell you that we have burned nothing but "super" unleaded in our own vehicles for many years. We have driven them a lot and have experienced no valve or seat failure.) Well, that solves the lead question.
The other question - that of octane rating - is a little more complicated. In their stock forms, the early 102 hp, all turbocharged engines and all 140 hp engines really require "super" unleaded. That means 90+ octane or better. All the other engines can probably run on most "regulars" although the miserable 86 and 87 octane unleaded fuels found around the country may be too cheap. Follow the basic rule if in doubt. If you get constant detonation (pinging) try to slightly retard the timing. If you have to retard the timing so much that it effects the power (and you don't have other mechanical problems) then you will either have to use more expensive gas or "alter" your engine. And just how do you alter your engine?
If you are going to rebuild the engine anyway then this is the best time to plan your "low-octane" modifications. Mostly you will be trying to lower the compression ratio, which can be accomplished the easiest by using extra thick head gaskets and barrel gaskets. If your heads have been "milled" or you have gone to one of the larger overbores (.040 or .060) this is advised anyway. These extra thick copper gaskets are listed on page B-6. Staying away from milled heads, exotic camshafts and the like will help, of course.
If you are not planning to tear the engine apart then there are still some things you can try. Be advised that some of these "add-ons" may or may not allow you to burn trash gas. Dale manufacturing makes "recurved" distributors that are custom-made for each engine. (Because of the complexities involved we do not handle these distributors but you can contact us for information on them). Water injection sometimes work well but they seem to have gotten hard to find and a bit expensive. A last resort is to use octane booster although that is quite expensive and should not be necessary in normal use. We used to carry some octane booster with us in the 180 turbo when we go on a long trip in hot weather because you never know when someone in Gritzl Forks*, New Mexico may slip you 75 octane gas on a 120 degree day!
Anyway, when it comes to the Corvair we have it pretty good. We can burn unleaded, gasohol, whatever, as long as the octane is high enough - this should guarantee that we can keep driving our cars as long as some sort of gas is available.
* A fellow from New Mexico asked me where Gritzl Forks was. I told him I didn't have the slightest idea. You get the picture.