timing advance curve

[Anonymous]

I know there have been posts about this, more specifically the springs being used for centrifical advance. Can anyone direct me to the past posts, or can help. I have a 66 mustang 200. All stock except Pertronix ignitor and 40,000 coil. Now I'm changing to a 1968 distibutor, and a weber 32/36 carb. First of all we are looking for 32-34 degrees of advance all in by 3000 rpms. This amount of advance is the total of base timing+vaccum+mechanical/centrifugal. Secondly can anyone recommend the amount of timing advance at various rpm's:
500 rpm's
750 rmp's
1000 rmp's
1250 rmp's
up to 3000 rpm's
Thanks Lowell

 

[wsa111]

Lowell66, needs more information about your engine, such as camshaft, compression ratio, transmission & even what degree thermostat you have in your engine before one can come close to the proper spark curve. William

 

[CZLN6]

Howdy Lowell:

I believe that MarkP posted a suggested sprng combo of a later model DS II distributor. Do a search for MarkP posts and you will find it.

Take vacuum advance out of your plotting and advance cure equations. Determine your centrifugal advance max, add in initial and then hook up vacuum advance on top of that. If you use a max of 36 total, (initial + centrifugal) the vacuum should work out fine for most mild engines, at or near sea level. The vacuum advance goes away under load.

I would suggest that you replace on of the centrifugal advance springs for one of the lighter ones in a curve kit, and then plot the curve. Be sure to do all plotting with the vacuum advance disconnected and plugged.

I seem to recall some differences with turning the weights over too, but it's been a while since I've played with anything but DS IIs.

I wouldn't worry too much about an absolute plotting curve. Just make sure all centrifugal advance is in by 3,000 rpms or less. It may not be perfectly exact for your engine and circumstances, but it will be better then stock and a step in the right direction.

Adios, David

 

[Anonymous]

As was mentioned the 36 degree benchmark is the total of initial and mechanical with the vacuum line disconnected and plugged. From 500 to 750 rpm, you basically do not want any change in timing due to centrifugal. You want centrifugal to kick in at a bit higher rpm level say 900 or something above 1000 rpm, that way you insure that your idle at 500 to 750 rpm is stable and not hunting around due to the centrifugal advance trying to come off seat. At idle, with the vacuum advance connected, The centrifugal advance would be zero and your combination of vacuum and initial timing should be something around 25 degrees of total advance depending on the engine configuration.
Doug

 

[kirkallen143]

At idle, with the vacuum advance connected, The centrifugal advance would be zero and your combination of vacuum and initial timing should be something around 25 degrees of total advance depending on the engine configuration.
Doug

That's if you are running the vacuum adv off the manifold side, if you are then you need to compensate by running a lower initial setting on your timing. If you use the port side of carb for a vacuum signal, then you can run the initial timing higher. Either way, they both work, but I like using the port side for a signal, myself. Hopefully more will chime in on this.

Kirk