vacuum advance ?

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a68postcar

a68postcar

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someone break down the diff. between a point type and a electronic type.ammount of adv. for each would help. but really,what i wanna know is, will one replace the other? my elec.vac pod is leaking @ the diaph. and i have a point type but the adv. rod is hooking up to the second hole(outside) of the adv plate.i know the throw is diff. but how much.will it work?
 
I was under the impression that all vacuum advance modules points, electronic, 6 or 8 would physically interchange. I have swpped them around to get different advance amounts. The number of degrees they add is stamped on the arm (double it for crank degrees).

However, if the one you are trying to swap in won't mount into the same hole on the advance plate will give either more advance if its closer to the pivot or less if further away. I wouldn't mess with it and would just go to the local parts store and buy a new one for your car.
 
i ordered a new one for it. i was just wondering if the amount of adv. throw was due to the dwell that was necessary for point vs. elec.. the reluctor / magnet setup must make it different due to sensitivity of magnetic field or something. l'm gonna do some more research to maybe find out and i'll post something on my findings.like i say, i was just wondering. i like to try to find answers to these little questions. they make me feel a little more knowledgeable. and it may help someone else along the way. thanks dave i appreciate the help. postcar.
 
The amount of advance the vacuum advance can adds has nothing to do with whether the distributor is points or electronic. Dwell is the amount of time in degrees the points are closed or in the case of electronic the time the output transistor is turned on, in either case its the time current is flowing through the coil. Typically an electronic ignition will have more dwell than points because the switching happens faster.

The vacuum advance changes the point at which the points open or the transistor shuts off in relation to top dead center of the piston. Vacuum advance is used to add additional timing under light throttle cruise conditions when the cylinders are not filling with mixture efficiently. Because of the inefficiency it takes more time to ignite it. Regardless of throttle position you want maximum cylinder pressure to occur at approximately 20 degrees after top dead center for the cylinder to generate max power. The vacuum advance adds or removes timing based on engine load and the mechanical advance adds or removes timing based on rpm. Both are tuned to try and provide that max cylinder pressure to occur at 20 degrees ATDC.
 
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