Timing

Black Girl said

Gentleman. My 360 smog block, alum head, 204/214 cam, stock converter, 69 dart likes 20 initial and 38 total. I'm using today an fbo plate at the 18 slot and changing the heavy spring for the light one in the kit.
I have slight detonation at hard throttle. Should I switch to the 16 slot or jump up to the next spring? Thanks guys!

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In upper rpms the mechanical advance is probably maxed out, so any further spring changes will likely make zero difference.
Try the 16 position of your advance plate.
38 total seems a bit too much anyway.

Or, just pull the base timing back a couple of degrees.
That will bring your total down as well without having to mess with the limit plate.