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I have a 1963 Catalina with a 1974 455 bored .030 with 6x 400 heads, I just finished rebuilding the engine, and I'm curious on what to set my initial timing at, I run premium gas in it so that means I can advance a little more right?
I would do it by trial and error. Start with bumping it a degree or two above stock and see if you get any pinging on WOT with the gas you are using. Find the spot where it begins to ping and then back it off one degree.
Use a dial back timing light and a Mr Gasket spring kit for either the HEI or Points distributor. Set your total mechanical advance to 36 degrees. The initial timing will be what ever that setting produces typically in the 12 to 16 degree range.
Not really, just read alot over many decades and have done many stupid things and some smart ones. Almost any GM V8 engine with cast iron heads and straight valve arrangement, as opposed to hemi or staggered, runs best at 36 at about 2,800 RPM with 93 octane gas providing compression doesnt get too high.You should also limit your vacuum advance to another 10 to 12 degrees.
That is a good starting point but for best performance you have to set for total timing as suggested above. I assume from picture you are running tripower? You did adjust the center carb idle mixture screws? You are sure you have no vacuum leaks? A full tank of gasoline, virtually no room for condensation, sits in my cars from December through April and it doesnt go bad. You are using 93 octane?