I use an MSD dist. with an Ice Ignition box and coil. If I lock my timing, it will pull timing and if I remember correctly, it pulled 3* at 4000rpm. It will not pull timing with a curve in it, so I ordered some large bushings from Don@FBO and now run 30* initial and all in at 36*. I think it reaps all the rewards of being locked and without timing pull. My box has a 10* start retard.