[bentwings]

Looking at the Accel instructions...
1 turn out vac adv starts about 8in all in by 9in. about 3 crank deg.
9 turns out vac adv starts about 4 in all in by 11 in about 29 crank deg.

It seems to be pretty linear in terms of turns , deg, start point and end point.

Poor resolution on the instructin page.

The adjustment seems to be for motors with quite low vac at idle. It looks like you put this thing on and you will get most of the vac adv travel below 10 in except for the very long adv adjustment. This is all in by by about 11 in.

More than likely going from no vac adv to active vac adv will pick up vac and it simply will give full dialed adv when you plug it in.

I have a hand vac pump and gage so I'll give it a test before I install it tomorrow night. Assuming I don't do something stupid like I did the last time I installed the vac adv. haha

[Custom10]

I have done the same bench test with a crane unit. Used a pump to see what the start of travel was in "hg and then what the end point was in "hg compared to turns out on the screw.

The crane unit always has the same length of travel on the actuation rod so the amount of vacuum advance added is the same for the entire adjustment range. Crane uses the limiter plate for a way to limit the amount added, accell uses a "one screw fits all" method and must have an end stop in there that is changed via the set screw, the screw must change the spring zero or start point at the same time it changes the limit of travel.

Two ways to skin a cat I suppose.

The advantage to the accell unit would be on an HEI application (if it does what they say it does). The crane limiter plate adjusts both the base timing (moves the reluctor static position) and the actuator rod starting vacuum in " hg (shifts the spring range up) as well as the limit when the plate is adjusted, it is mounted on the back side of the rod. When you adjust the limit on the accell HEI unit with the screw you are not changing the initial timing as it increases the allowable limit without moving the reluctor becuase the limit is on the front side or end of travel on the rod.

[bentwings]

I believe you are right on the way the Accel unit works.

Time will tell whether it works.

My main interest is getting the idle leaner and adding at least 10 deg timing right in the idle range. This will bring back the mpg I have lost as this is how it originally worked before I blew out the vac diaphram.

Additionally I need to look at a way to bleedoff boost to the vac adv unit.

I have to check again how much vac there is under the carbs at full boost and in the 5000-5500 range. If it is less than 5 in I can just hook the vac adv to the carbs as the vac adv does not start until after this.. I have a cheezy check valve that is supposed to go to the vac modulator but I have not used it. The thing is just a tee with a ball check in the vertical leg. Pressure lifts it up and there is no pressure on the diaphram.