I am getting ready to put my new distributor in and have a clear cap for adjustments from Rick Gorski. Where in the cycle of the rotor tip to cap terminal does it fire?? Does it fire through the whole contact area, more towards the middle or ends? Just trying to see where the optimum adjustment is, I would think the middle but looking to see if anyone knows!! Thanks!!

I want the rotor and post centered at max advance.

it fires as the reluctor blade "just" moves away from dead centered on the pickup magnet. How long the spark duration is, I do not know. In addition to RP you want the rotor tip to be close (.015" is ideal) radially to the cap terminal at WOT when the available voltage is the lowest (less coil saturation time due to high RPM) and the required voltage is the greatest (cyl psi is the greatest) & if you set RP so the rotor tip is on the trailing edge of the cap terminal you are good as vac adv shifts RP back CCW on a SB & CW on a BB. keep the rotor/cap brass terminal edges sharp with a dremel cuz it takes lees voltage to jump from sharp edges than dull edges & get the circumferential clearance (RP) corrected & reduce the radial clearance to .015" by drilling out the rotor rivet & subbing in a piece of brass. NAPA has an Echlin rotor MO3000 for $8.xx that has an .060" longer blade. let the eng idle & plug the can into manifold then pull the hose/cap the nipple & see where the rotor retracts to to see where you are at. Easiest is redrill new hole(s) in the reluctor to rephase. I forget the drill bit size & drill a hole a bit out from the center hole ID then open it up back to the ID with a mini round rat tail file. Note that only vac adv not mech adv changes RP.

MSD has an adjustable rotor, works good.
Part # 84211.
I have extra one if interested.

Very good info there!! I don't run the vacuum advance, I just cap it. I think for starters I will try the Echlin rotor and look into the MSD adjustable one to see if it will benefit me, Thanks for the offer Steve!! One thing I have noticed in the last few years is that a lot of caps are not turned very true and have thicker terminals on one side of the cap compared to the other and I don't know how that will affect certain adjustments and adjustable parts. A guy last year at the Norwalk Mopar event had a bunch of the Accel brass insert caps and everyone was off center to some extent, and I have seen others as well. Thanks!!

Right now I would just start it/std rotor in there & see where the circumferential phasing is & the radial clearance & yes the poor cap quality control/manufacturing tolerances makes that (radial) clearance more difficult (ideal is .015" at the tightest terminal) but most are way more apart than that even on a perfect "circle".