I disagree.... regular is fine in the stock "low performance" C3 Vettes of the mid- late 70s, early 80s. If your ears are good enough to detect detonation, one could always retard the timing back a few degrees. My rule-of-thumb, if it has a cat, regular is fine.

I am running a ZZ-4 in my '78 with 34 degrees of total timing advance and don't dare run anything but premium. The L-82 I pulled out of it sits in my '38 Pontiac and eats regular just fine with the same 34 degrees of total timing. When I swapped engines I pulled the heads off the L-82 which had always been fed a diet of regular and there were no signs of any detonation.

Dave

You should run the lowest octane you can with out pinning. High octane does not give you more power. Octane inhibits detonation so you can advance timing. You will get more bang out of reg. gas. Just make sure you don't have any pre-detonation.

Hi guys, I've got a 68 427, bored .060 over, with 11:1 slugs.  Tatal timiming of 38 advance and I always use the low octane, but use 104 booster and a lead additive and the engine runs great

How can I be sure of that? --pre-detonation   Rich rich2219502007-04-20 19:03:55

You will here it pinging (also called knocking). With 11:1 compression there's a good chance you will need premium fuel. Just try the middle grade and see if you get pinging, if you do go back to premium, if not try the reg. Run the lowest octane you can & still have a good running car.

Thanks for everyone's input, I'm new at this and appreciate all the help. Since running premium only and it runs good with no pinging, I guess I'll stick with that.  Rich

My 81, will not run properly on regular.  I hate to say it but I dont think any of us wouldnt use prem if we had to or worry about gas milage.. lol..

Mine does not like reg. She wil burp and stall and just run poorly.  91 or better for me.