We were discussing octane earlier. Note the (R + M)/2 you see on pumps in U.S. This average of the RON & MON ratings is also called the PON rating referenced earlier where I stated:
In your 1964 Owner Manual on page 36 it indicates to use Minimum of 100 octane RON, or 89 octane MON. If you do the math to get the PON # that comes out to 94.5. So..that means the 93 Octane Premium in the US (PON) and the 99 Premium in the UK (RON) are both just tad lower than the recommended minimum octane for our 10.5 to 1 compression engines. My 64 CDV runs fine on 93 Octane, however, adding octane booster seems to give it more power. Keep in mind that the 94.5 would be a minimum recommendation and not an average or maximum recommendation.

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Comment by Che Gallagher on February 11, 2022 at 5:52pm
Thanks for all the comments it has definitely been helpful i now have a good knowledge of how it all works and what i need to do. Thaks everyone
Comment by Tony and Ginny 429 on February 11, 2022 at 12:22pm

You want to be sure your spark plugs are burning the correct color to get the best from the gas you are using 

That will tell you a  real lot about what  you need to know regarding  the gas you are using and how your car is performing  ( one of the best indicators )

The plugs SB burning a brown paper bag color 

If whitish your are lean ( will cause cylinder heat )  and if darker you are running rich ( burning more gas than necessary )

Using 93 octane you can rejet the carb until you get the correct color on the  plugs and then  you will have the correct cylinder temps going on 

When I changed to the Edelbrock 1406 carb  ( from the  stock Carter ) now on my 64 -429 I had to  change the jets and metering rods in the primary’s  two steps richer which I did with the  help of the Edelbrock tech as I was burning my plugs lean when first installing the carb and inspecting the plugs performance 

Lean plugs can be the result of a vacuum leak ( unwanted air getting into the intake manifold ) that needs to be addressed before any jetting of the carb —that only SB done at the end of a very complete engine tune up  —-to be tweaking that tune up for max performance 

This will help getting the most performance  from the gas you are presently needing to be using in our Classic Antique Cadillacs in 2022 

Yes —these engines produced a good deal more HP with the higher octanes available when our Cadillacs were new 

93 octane is about as low  as you want  to go  and be ok with a  10.5 :1 compression engine as we have in the 390 and 429 engines we are driving in 2022

Enjoy  

Enjoy 

Comment by Tony and Ginny 429 on February 9, 2022 at 2:19pm

I have been using 93 octane in my 64 - 429 for a very very long time with no issues at all and I run my timing at 8 degrees not the stock 5 degrees with no sign of pinging but I never floor my car and abuse it — ever !

I myself am not a fan of gas additives due to the constant  thought and expense involved but I always use Marvelous Mystery oil to lube the valve guides and top of the cylinder bores 

When our  cars were new the gas was 103 octane at most stations and Sunoco offered 110 octane

( highest octane )  from there select pumps 

I do not see any value in using the 89 octane non ethanol gas as the rating is to low for our cars these days 

I can tell you from using the higher octane back in the day  that there was a very reasonable noticeable increase in HP  and performance these cars produced using those octane ratings which is always a wonderful enjoyable experience and a different driving experience for those reasons 

Not really sure how the octane ratings have changed over the years or when exactly those changes have taken place for us to now have arrived at the present 93 octane rating for our high test gas we now use - but it is what it is —and glad it works well  in our Cadillacs in 2022

Just a little history for you younger folks that have not lived thru those changes 

Enjiy 

Comment by Ian Osborne on February 9, 2022 at 11:01am

It's actually the exhaust valve seats that are replaced on older engines to be able to run unleaded fuel in an engine that was not designed to do so. An insert is pressed in and a new valve seat cut into it.

Comment by Tony and Ginny 429 on February 9, 2022 at 12:31am

Micheal 

They replace the old valve guides with new harder  valve guides to handle non- leaded gas 

So a good time to have a machine shop freshen up the heads ( top end ) 

Enjoy 

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 Che Gallagher on February 7, 2022 at 6:30pm
With the 429 engine can you just run it on a unleaded or do you have to add a lead additive to it
Comment by Ryan Trask on September 13, 2012 at 1:50am

awesome thanks for this info! this might explain why my car runs a little rough sometimes, as i have been using 89 octane. ill switch it to 92 (since that's the highest i have in my area) and try a little booster

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 Russell DeBarros on September 2, 2012 at 8:31pm
So then my question is, "does running the vehicle with lower octane fuel consistently do any damage, or is it just a question of optimal performance? I for one have been running regular unleaded with lead additive and feel that my car is running great especially since I just tuned it up a bit.

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