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 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.
Comment by David Murray on September 2, 2012 at 4:01pm

Come to think of it, I put a dose of lead additive in the tank everytime I fill up and the label says that raises the octane a little, so I guess I'm probably at, or around, 100 PON

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.

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