Vacuum advance issue

Last of the Fast said

I have a 1970 Duster 340 that needs 100 octane gas (stock). In order to make it run on 91 octane (California), I disabled the MECHANICAL advance and run initial at around 10 degrees, and then tailor the vacuum advance to yield the most advance without pinging. I outran a 1969 Hemi Road Runner with this car, so does it work? Ohhh you betcha!

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Yes it can work. The intended function of vacuum advance is to improve fuel economy under light load cruise conditions. Mechanical advance is to accomodate the fuel burn rate and engine RPM to attain max cylinder pressure at somewhere around 15° ATDC. Your cam and compression will dictate initial timing. Mechanical advance can be tuned for max advance and how fast it comes in.