Base timing. Really ?
Since your working with a 440, its worth looking at factory 440 hi performance timing.
This is the range that was acceptable for Plymouth when inital was set at 12.5 BTC (or 5* BTC for a smog distributor).
Many of the electronic distributors have a timing curve that is something like that that '67 CAP timing advance.
These CAP and CAS advances used a fast and long primary advance to get the off-idle timing back where it should be for efficiency. (The late timing at idle was neccessary for more complete burning of HC and reduction of CO.)
The above timing curves work well with vacuum advance. Thst long slow secondary advance also works well with electronic ignitions as it helps offset the slew rate that Yellow Rose posted about.
So when we take early emissions era Chrysler distributors and shorten the inside slots, we get somethng like this.
Now with good fuel and at reasonable elevations, we can often advance that initial somewhat. If doing so increases the mph at the track, then thats what it wants.
In contrast, here's an example of limiting the top end of the advance for a '68 440 manual smogged distributor.
This might have worked good at the drag strip with dual points and no vacuum advance.
Its completely unusable with vacuum advance and if used with an electronic ignition will retard timing at the top end.
Since your working with a 440, its worth looking at factory 440 hi performance timing.
This is the range that was acceptable for Plymouth when inital was set at 12.5 BTC (or 5* BTC for a smog distributor).
Many of the electronic distributors have a timing curve that is something like that that '67 CAP timing advance.
These CAP and CAS advances used a fast and long primary advance to get the off-idle timing back where it should be for efficiency. (The late timing at idle was neccessary for more complete burning of HC and reduction of CO.)
The above timing curves work well with vacuum advance. Thst long slow secondary advance also works well with electronic ignitions as it helps offset the slew rate that Yellow Rose posted about.
So when we take early emissions era Chrysler distributors and shorten the inside slots, we get somethng like this.
Now with good fuel and at reasonable elevations, we can often advance that initial somewhat. If doing so increases the mph at the track, then thats what it wants.
In contrast, here's an example of limiting the top end of the advance for a '68 440 manual smogged distributor.
This might have worked good at the drag strip with dual points and no vacuum advance.
Its completely unusable with vacuum advance and if used with an electronic ignition will retard timing at the top end.