recommended timing curve for 1970 300 vert

[challenger]

I ordered springs for the Mopar/Mallory YH style distributor. I am trying to lower the total timing including vacuum advance. I've been getting detonation at highway cruise speed. The distributor is a Mallory with a 9" canister which gives over 20" vacuum advance. The distributor mechanical advance is adjustable but the timing comes all in too early. With 13* initial timing I am reading well past the 50* max on the timing tape-looks like almost 60*.
What curve do these heavy cars need? I'd like to keep the vacuum advance adjusted as it was originally for economy as well as have good initial timing. When set at 12* the vacuum is only about 15". I have an edelbrock 1411 750 cfm carb.
Thanks
Howard

 

[Husky]

Mopar B/RB engines run best with total mechanical advance of about 38 deg and with an aditional vacuum advance of 20 deg taking it out to a maximum of 56 degrees. If this 50-60 degrees you refer to is mechanical advance only, then you have way too much. Also the problem with many of these aftermarket distributors is the advance curve is too rapid. You need springs such that with an initial timing of say 10-15 degrees, you get an all-in 38 degrees mechanical advance at 2500-3000 rpm (preferably closer to 3000 rpm for a heavy car with tall gears). 20 degrees of aditional ported vacuum advance on top of this will provide good throttle response and fuel economy.