what fuel should I run in my 1968 GTO with 400 big block 4bbl?
It has been so long since I put gas in a car this old I don't remember if we were still using
leaded fuel. I was working in gas station in 1970 and remember selling gas for 23 cents
per gallon with different octane ratings but I think all the grades contained lead.
That's correct. Any GM made before 1971 used leaded gasoline. Your GTO requires premium. I used to fill up my '70 Catalina, with the same engine, with premium, lead substitute, and octane booster at each fill up. Without the octane booster it would diesel when I shut it off. HTH. - Jim
Back then the octane ratings were a lot higher than they are now, I believe that engine used premium fuel and that was 101 octane, so now you can't get that fuel, so you have to buy the highest octane you can get, put in a bottle of StaBil Marine additive, this helps with the ethanol in the fuel, then add some lead substitute, that's for the old valves and seats, then try it, if the engine pings then you have to add a bottle of Octane 104 and hope that does the trick. There was a time when you could get 101 octane from an airport, but I don't think you can do that any more.
I was to working in a gas station and it was .53 c a gal boy would it be great to pay that again
You can use avgas... 105 octane, or race fuel... 110 octane.
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