Ported Vac or Manifold Vac

alsant said

sorry been busy
It’s a 318 .40 over
340 cam
68 heads
QFT 680 cfm
Edelbrock LD4B
4 speed A833
Block is a 73

I’ve rejet the carb for 5000’ , need to do more to the carb
Need to change springs on the distributor , right now advance is coming in till about 3500rpm

Thanks

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First thing you need to do is measure and plot the timing vs. rpm.
If the distributor is a factory pre-68 49 state then that's a good baseline.
If its a Chrysler built MP distributor, that too is a good baseline if it hasn't been mucked with. When you have time you can do a search and see what I've found with those, along with the guidance from MP.
If its a Chrysler distributor from the smog era, its hard to know what you'll find, but oiften those have a quick and long primary advance. With those sometimes an effective crutch is to use manifold vac advance to get the initial timing up after start. Dpends on the details of the advance and how well the engine idles.