Hello! Was wondering your thoughts on best fuel for L48 with Rochester Quadrajet. Do you suggest adding boosters and other additives to ratchet up octane # of pump gasoline? When fueling, do you guys fill up, or do you fuel little to force yourself to continually add fresh gas? As always, thanks in advance!

A stock L48 can probably live just fine on low grade, or at worst mid grade gas.  The bigger concern is the ethanol in today's fuel - it eats rubber and causes corrosion in our tanks, lines, pumps, and especially carbs.  You can look for a station with ethanol free fuel - I just moved to a new place and the little country store right by it has super without ethanol, but it's not cheap.  There are other additives that can help with the ethanol, but I would not think you would need an octane booster.  If you ever rebuild the Q-jet, make sure you or the builder uses a quality rebuild kit that is designed for today's ethanol fuel.  

 It depends on where the timing is set, really. I only put premium in my '74 L-48.....and it will still ping a little when hot. My timing is set to factory specs, too. I would like to add some timing to it, but it would make it ping worse.
My opinion is to buy the best fuel you can get, that it will run properly on, whether that is Regular, Mid-grade, or Premium. The L48 should be able to operate on mid grade fuel, but fuels today are NOT what they were back then. Ethanol is only part of it, but it certainly adds to the problem. Octane boosters are simply a way to get you to part with your $$$ with no real improvements. The situation is only gunna get worse, too.....

I only run 91 octane or better and if they have 93 I run that exxon or mobile  with stock carbs

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I run high test with no problems, and that's with 17* of timing.  If I'm not going to drive it much, I'll put some Stabil in it.

What about the method of using the lowest grade that doesn't cause pinging?  My car with 9.4:1 compression and about 18 degrees of static timing doesn't seem to ping at all on mid-grade.  I usually do use premium but tried a tank of mid-grade a few tanks ago and I didn't notice any pinging.  I've always understood that using a higher octane than necessary is just dropping unnecessary $ in the tank and that the actual quality of the gas doesn't really change much with grade but maybe that logic is out of date?  I've attempted to educate non-car types in the past that putting super in their plain jane car is just a waste of money - go by what the owners manual says - but I know that system doesn't really work for a 70's Corvette.  

Thank you for the replies. I just had my timing and dwell set back to factory yesterday. They were off quite a bit. Because I was really low on fuel, I went to the station and filled up with 89 (mid grade). In south east Wisco we have 87, 89 and 93. So far, she seems to be running fine, but what is this "pinging" you guys refer too? What am I looking for when deciding which gas she likes best?

Here's something I forgot to mention: when the car is idling, like at a stop light, I'll occasionally get this phantom rumble from the engine. It's not missing or skipping, it's just this rumble-like feeling. Kind of comes out of nowhere. Is that the pinging you're referring to?

 If you've ever heard a diesel engine run, you've heard "ping". On a gas engine, the ping is a little less intense/loud, but it's the same noise. Ping, or pre-ignition knock is caused by high cylinder temps and pressure. Too much timing, too much mechanical compression, and low octane fuel all contribute to the problem. "Ping" is the noise the piston makes when it rocks inside the cylinder wall. There is a normal amount of piston rock due to the clearance between the piston skirt and the cylinder wall. If the cylinder temp gets too high, the piston will rock violently, and the noise is actually audible.

The "rumble" sound you hear is something different. Could just be exhaust resonance, or it could be a heat shield, or other item vibrating and causing a rattle. Hard to say without actually hearing it.