Timing

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!