dist advance vacuum unit question

[valiantwagonguy]

Yesterday I was rebuilding a distributor for my 66 Valiant convertible.It's a 225 slant.I was taking 4 different distributors apart for good parts and noticed that every one had a different value stamped on the arm that connects to the advance plate.There was 6.5 , 7.5 ,9.5 , and 10 . I'd like to buy a new unit but have no idea which one to get.The car has a 1 bbl and a 904 automatic.It's bone stock with 59,000 miles on it.So,is there anyone out there who knows what the correct one would be ?

 

[my68barracuda]

Yesterday I was rebuilding a distributor for my 66 Valiant convertible.It's a 225 slant.I was taking 4 different distributors apart for good parts and noticed that every one had a different value stamped on the arm that connects to the advance plate.There was 6.5 , 7.5 ,9.5 , and 10 . I'd like to buy a new unit but have no idea which one to get.The car has a 1 bbl and a 904 automatic.It's bone stock with 59,000 miles on it.So,is there anyone out there who knows what the correct one would be ?

The numbers on the arm of the vacuum can are the number of distributor degrees that can is capable of advancing the distributor. You will need to double that to get crank degrees.
The vacuum cans with a hex shape on the end where the vacuum hose attaches are adjustable by using a small Allen wrench inserted into the vacuum hose attachment. You can test the vacuum cans to determine if they hold vacuum and also to see the effect of the adjustment by using a hand vacuum pump. I use a cheap vacuum brake bleeder pump from Harbor Freight. Vacuum advance is used to improve fuel mileage at steady highway speeds. The cans with the lower numbers are typically from heavier vehicles to limit the vacuum advance to reduce pinging. The higher numbers are for lighter vehicles to allow more advance. Although ether can be intermixed to hit a desired advance depending upon how much initial advance is dialed in and how much centrifical advance is built in depending upon the springs and the regulator.

 

[my68barracuda]

The numbers on the arm of the vacuum can are the number of distributor degrees that can is capable of advancing the distributor. You will need to double that to get crank degrees.
The vacuum cans with a hex shape on the end where the vacuum hose attaches are adjustable by using a small Allen wrench inserted into the vacuum hose attachment. You can test the vacuum cans to determine if they hold vacuum and also to see the effect of the adjustment by using a hand vacuum pump. I use a cheap vacuum brake bleeder pump from Harbor Freight. Vacuum advance is used to improve fuel mileage at steady highway speeds. The cans with the lower numbers are typically from heavier vehicles to limit the vacuum advance to reduce pinging. The higher numbers are for lighter vehicles to allow more advance. Although ether can be intermixed to hit a desired advance depending upon how much initial advance is dialed in and how much centrifical advance is built in depending upon the springs and the regulator.

The regulator, that is the slotted steel part that limits the travel of the weights may also have a number stamped into it. That marking will identify the distributor degree advance potential of the centrifical advance mechanism.
You may also notice different spring lengths and wire thickness. Those control the shape of the centrifical advance curve.
As a general rule, lighter vehicles can take more advance early, for improved performance and acceleration snap. Heavy vehicles will use a less aggressive advance curve to advoid pinging. Do some internet searching on ‘distributor curves’ and then maybe build up a couple of distributors, with different curves and vacuum setting and see what works well for you.

 

[valiantwagonguy]

The regulator, that is the slotted steel part that limits the travel of the weights may also have a number stamped into it. That marking will identify the distributor degree advance potential of the centrifical advance mechanism.
You may also notice different spring lengths and wire thickness. Those control the shape of the centrifical advance curve.
As a general rule, lighter vehicles can take more advance early, for improved performance and acceleration snap. Heavy vehicles will use a less aggressive advance curve to advoid pinging. Do some internet searching on ‘distributor curves’ and then maybe build up a couple of distributors, with different curves and vacuum setting and see what works well for you.

Thanks,that was the info I was looking for.