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Comment by Michael Vogler on February 8, 2022 at 9:56pm

The lead in gasoline helped reduce engine knock and acted as a lubricant on the valve guides in these old engines.    

I was told by mechanics on each of my vintage cars (two '65 Mustangs and two '64 DeVilles) that running the car without the lead additive may, over time, damage the valves, resulting in an upper engine rebuild (unless the engine was rebuilt with modern stuff). 

I always put in the highest octane gas I can find and lead additive when I fill up.  Certainly doesn't hurt.   

Mike

Comment by Jason Edge on September 2, 2012 at 9:22pm

I'm not sure how much lead additives raise the octane (if any). These higher compression engines were made for higher octane gas than the 80 something regular stuff they sell now. There is a lot of information on octane and engine compression out on the web. The best my car ever run (well before I rebuilt the engine) was on a strong dose of the 100+ octane AV Gas. I can remember here in NC growing up in the late 60's and early 70's where Hi Test was 95 to 98 octane and 93 would be more or less mid-grade.  The diffference was there were still many high compression engines on the road and being produced and the low compression 9.0 to 1, 8.5 to 1 and lower compression engines were just starting to replace these older high compression cars.  The new cars with low compression engines and electronic ignition that can automatically adjust timing as needed can burn the low octane stuff but I would never recommend putting regular in a 10.5 to 1 compression 390 or 429. 

Comment by Jason Edge on September 2, 2012 at 2:54pm

tagged as octane, octane rating, and fuel rating and set-up URL http://6364cadillac.ning.com/photo/octane for easy reference.