retard timing mechanically?
Yes you can run a dual pickup dizzy Mr Dedman and myself are running one in our slant turbo valiants . I believe most were found in the lean burn era mid 70's. You can run a Hobbs switch of some sort to switch between the two pickups. Ideally a dual set of contact switch that under vacuum one pickup is live and under boost the other on retards your timing.
The member on. Org who I bought my dizzy from told me there's about a 8° difference between the two pickups.
I never hooked mine up this way because I like the 6530 because it has different rev limits plus timing control and data logging....
I hope this helps
What Aaron said about our car was true as far as it went, but, here is some more information... for your perusal...
What we did was to order a rebuilt
dual pickup "Lean Burn" distributor from Rock Auto, which has
NO vacuum diaphragm, and
NO centrifugal advance mechanism in it to advance the timing at all.... it is essentially, a locked plate that cannot move to change the spark setting.
Simple...
The idea was going to be, to use one of the pickups for starting (retarded, to keep the engine from "kicking back" on the starter,) and switch over to the other pickup for all other running, using a "
double-pole, double throw" switch that would de-activate one pickup, while simultaneously activating the other... thereby advancing the spark for general driving. One flick of one (dp-dt) switch would do it all...
I began trying to find out how much difference there was in the placement of the two pickups to learn how many degrees of spark advance (or, retard) difference there would be, from one pickup to the other.
I searched for days and
never could find out.
So, I decided that I would just hook up a timing light and check on the damper, and see what happened when I switched between the two pickups.
But, the thing ran so good on ONE pickup, set at 18 degrees of advance, and had NO "starter kick-back" at all with just the one pickup hooked up, that I never bothered to hook up the second pickup, so, I still don't know.... because I don't use the second pickup.
This engine seems to run perfectly well with NO spark advance curve... runs cool, has a ton of power, starts on the first hit... and idles at 500 rpm, smoothly. We don't need no steenking spark advance curve!!!
Admittedly, it is turbocharged (10 pounds of boost) and is a
race-only engine, with no street driving in its future, so the demands on it are minimal when it comes to driveability, but, knowing what I know, now, if I wanted to drive it on the street, I think I would just replace this distributor with another "locked plate" Lean Burn distributor, that had a vacuum advance canister on it, and hook it up to manifold vacuum. The vacuum unit would advance the spark for fuel economy (cruising) and cooler running while there was no boost being made, and revert back to eighteen degrees of advance (where I would set the timing with no vacuum,) when I opened the throttle, vacuum disappeared and boost came on.
I can't see why this would not work. The absence of a spark advance curve doesn't seem to affect the way this engine runs at part-throttle at all. Weird!!!
My 2-cents...