Your distributor is put in a tune-up machine and the advance springs are 'adjusted' to bring distributor advance in on an rpm curve compatible with the specs of your cam and other components.

If you're running a cam that produces max torque from say 1500 to 3500 rpm, that's where you'd want the advance spread. With say 12 degrees initial at the distributor and wanting a total of 36 degrees advance, that leaves 24 degrees to spread over 1500-3500rpm.

There are other variables. A stock torque converter stall speed is about 1500-1700rpm, but if you have an 'RV' T/Q, the stall speed is going to be 800-1200rpm and you don't want to wait for 1500rpm to start the advance curve. Likewise, high duration hp oriented cams usually don't start the torque curve until 2500-3000rpm. 4-barrel carbs with vacuum secondaries require X amount of vacuum to open the secondaries, and an aftermarket cam with high duration produces that vacuum at X rpm, and so on.

Most speed shops and engine builders charge about $35-50 for this service, and that's a lot less than buying a new electronic ignition. I'm not familiar with MSD ignitions (Mallory Comp 9000 fan), but the electronics might allow you to set the curve yourself. Perhaps someone familiar with MSD could address that issue.

 

MSD mallory, same stuff. They both got springs that need to be changed out to match your combo.

chris
79 F-150 Ranger Lariat, 2wd, RC, LB, 460 (intake, headers, cam), C-6(shift kit).

79 mustang (work in progress...its just slow progress)
98 Chevy 4x4 (work truck)
95 Lexus SC300 (wife's baby)