I finally have a chance to check some of the various ignition boxes I have on hand to see how they retard with RPM. At the moment I have a MP orange box, an early 1980's gold box, a Mallory HyFire IV, Mallory HyFire V, Mallory HyFire VI digital, and a Mallory HyFire VII analog. Tonight I tested 3 of the boxes and these are the results. Mallory HyFire VI digital box with a Mallory 29440 coil. Model number 685. -1 degree at 3800 RPM -2 degrees at 5000 RPM -3 degrees at 7500 RPM With this box, if you set your total of say 35 degrees at 3000 RPM, just 800 RPM's later you lose a degree. By 5000, you are at 33 total and at 7500 you'd be retarded back to 32 total. Mallory HyFire V analog box with a Mallory 29440 coil. Model number 690. -1 degree at 3500 -2 degrees at 4750 -3 degrees at 6200 -4 degrees at 7000 You can do the math. Mallory HyFire VII analog box with a Mallory 28880 coil. Model number 667. -1 degree at 4000 RPM -2 degrees at 6000 RPM -3 degrees at 7000 RPM -4 degrees at 9500 RPM Again, you can do the math and see the issue with locking out the timing, or not setting your total at max RPM. I can test these boxes to 12,000 if I want to. The machine will easily go that high.