MSD distributor mech advance limit ?

[73c34me]

Greetings, I made a limit bushing that allows 0.075" advance rotation travel at the cap. It appears to me that this is about 2 degrees advance at the dizzy- 4 degrees @ crank. This is my goal. Can someone confirm what the distance (0.075") would be in degrees of advance? Thank you
Note: I am making a late small advance curve to counter- act the msd "retard" phenom.

[bill jones]

-I did the same thing on a 1957 to 1974 style Chevy distributor---this is my notes form that project.
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GM/MSD distributor #10093387.
1-limit pin diameter is .190”----rotational diameter of pin = 1.120”----circumference = 3.5186”.

2-circumference of 3.5186” divided by 360º = .0098” per distributor degree

3-limit slot is .410” long---subtract the limit pin diameter of .190” = .220” of maximum rotational movement with no bushing installed.
---.220” divided by .0098” = 22.4º distributor degrees (44.8º at the crank)

4-width of the slot is .410” max----but a .410” bushing binds on the outer edge of the slot and down on the outside of the main stem.
---set up the distributor top advance section on the mill and bored the slot hole with a .472” end mill so that it cuts the outer edge of the slot and trims down the main stem a ways allows the .410” bushing to rotate freely about .040” to .050”.
---this means with the largest bushing that can be fitted to this modified situation there will be about a 4º to 5º minimum advance curve.

5-I then made a resilient limit bushing with a thin tubing outer wall---a short piece of rubber hose inside that fits onto the limit pin---used a retaining clip on the bottom end of the limit pin to prevent the pieces from working loose.
---this allows a mild advance curve to counteract the timing retard of the magnetic trigger once the timing curve stops.

[jed]

Thanks again Bill. "You the man" you have forgot more about making power than I and most of us ever will.
Thanks for being my friend.

[73c34me]

Much thanks Bill. I don't have a mill so a made the stop bushing with "flat" sides so that it would slide in the slot. Otherwise the diameter would be too large and the bushing would not fit. I also drilled the end of the advance weights to reduce mass at the outer edges, combined withe the stiffest springs. I am shooting for the advance to begin around 4k rpm.

[F-BIRD'88]

these easy to fabricate sheet metal tabs limit centrifugal adv weight travel

[Krooser]

What is this 'MSD retard phenominom'?

[F-BIRD'88]

What is this 'MSD retard phenominom'?

On pretty much and ignition amplifier ( that does not have built in compensation) when you run locked out advance,

The engine rpm gets ahead of the electronics. This results in spark retard at high rpm.
This can actually be a good thing on a drag engine, depending.....
Some spark boxes have built in compensation, Most do not.
This slow, limited amount and delayed mechanical advance curve that is delayed to come in starting at 4500++ rpm
compensates with a little bit of mechanical high rpm spark advance.