Timing curve for my big-cam 451?

Thanks. I drive it on the street, so I need vacuum advance to have some semblance of fuel economy, and cooling ;)

Tonight I experimented some more... took the dist apart, left the super-light spring in place but removed the heavy loop spring and used the OEM blue spring. Added the FBO plate to limit at 14 crank deg.

Then I fired it up and set the initial timing to 24 deg. Without the vac advance connected, it rises to 38 and starts to retard as before, but didn't go below 35. So far so good. I'll have to get a helper tomorrow to read the tach when the advance is all in. The advance begins right off idle, which is not good for stability - so I probably need a bit more spring. I may try using a pair of medium springs from the three pairs that came with the FBO plate.

The vac advance keeps the timing around 32-36 (it doesn't always return on decel to the same spot). And it's marginal to stay advanced at idle, although I'm up to 8.5-9" vac and at least 1200 rpm (the Autometer 5" tach is not the most accurate at the low end!) Max advance in neutral is 56 which may be too much. It won't be hard to add shims to the advance arm to limit it, if I have surging at cruise.