Ported Vac or Manifold Vac
The cam in my slant 6 has 250 degrees duration @.050" and it's ground on a 108 LSA. I have it sitting on about 22 degrees initial timing with 10 degrees mechanical and it runs really well. It's also a measured 10.6:1. It also runs better on manifold vacuum to the vacuum advance. But a mild engine will likely not benefit from that.
It goes full circle. I’ll say it again. IF you use too much cam for your compression you’ll likely need more initial timing than you can get and still get a curve.
Then you can use MVA.
I’m on the other end. At 12:1 (actual, measured not a guess) with 255 @ .050 and I’m betting I’ll need 20-22 initial. That can be easily done without MVA.
I will be testing with ported VA on the dyno and if it looks like I can use VA (ported) in the car I will.
The claim that every engine needs some absolutely insane amount of initial to get the idle correct is 100% bullshit and it needs to be called that.
Chrysler didn’t miss the boat on that.
Sadly, the OP has not done a search on here because this horse and 4,976,213 other horses along with it has been beat to death just on this forum.
Next up the “all in” or “lock it out” crowd will come along and exclaim that’s the only way to do it, when in fact its wrong 99.9% of the time.
I just wanted to head that off at the pass before it even starts.