dual pick-up electronic ignitian???

[Tawny Demon]

After doing some research this seemed possible...any imput or suggestions? Any obstacles to be aware of? Has this been done before?

I'm looking at wiring a dual pick-up ignitian from a 1986 Dodge Diplomat into a single pick-up ignitian on the electronic ignitian of my 1971 Dodge Demon using the concept of a dual point distributor but retrofitting the dual electronic system to a 1974 single pick-up electronic ignitian set-up.

 

[67Dart273]

I think you are off track.

I believe some guys used lean burn dist's which have no mechanical advance, in a race only situtation, and may have used the second pickup with a switch for a retard startup pickup. There is no way, and NO REASON to try and use them together.

The reason dual points came about was for two reasons:

1 They could operate at longer dwell periods than single points, because the time period of the two overlapped, and

2 Generally they reduced points bounce problems at high RPM

 

[Tawny Demon]

but if I run a fully locked out '74 distributor with no vaccuum advance canistor on it at all (originally did have one), would it be more practical to run this setup with a fully locked out distributor or convert it back to vaccuum?

 

[mcnoople]

You should only run a zero advance dizzy on an efi system. What is your intended use for this car? Drag car, daily driver? I have considered the dual pickup as an option if I ever went efi which will likely never happen.

 

[Tawny Demon]

street/ strip for 12:1 comp. small block 340 with Holley 850, 531/547 lift cam

 

[67Dart273]

but if I run a fully locked out '74 distributor with no vaccuum advance canistor on it at all (originally did have one), would it be more practical to run this setup with a fully locked out distributor or convert it back to vaccuum?

I think we need more info on what you had, why you want to change it, and what you expect to attain.

 

[Tawny Demon]

I had basically a stock distributor that I took the vaccuum advance line off. When I was told that that was essentially locking out the distributor or stopping advance, I decided it might be more beneficial to remove the vaccuum advance and stop the pick-up from advancing by tapping a hole to lock it down. Correct me if I'm wrong, but wouldn't that be the same as removing the vaccuum line and fully locking the distributor? Is there a way to modify the distributor to make it mechanically advance without using the vaccuum?

 

[TrailBeast]

I think it would just cut the dwell time in half and not fully charge the coil, unless I'm missing something.

 

[jos51700]

I think (no offense here) that eliminating advance, either mechanical or vacuum, is for the blatantly ignorant.

The dual pickup distributor is a beautiful thing, especially for boosted applications. Flip a switch: race gas/street gas, towing, boost, highway cruise versus race mode. You can bump your entire curve to something more or less aggressive with the flip of a switch. Neat!

 

[Tawny Demon]

What about mechanical advance with a dual pick-up that's wired in so that the second pick-up only activates with a switch?

 

[67Dart273]

That might very well work. My understanding is that some of the racers switch pickups one for startup, the other for run, with a locked distributor But the thing is, I see no reason to do that. If you have a distributor with a proper curve in, it takes care of itself.

Many guys who don't care much about mileage do in fact run ONLY mechanical advance, and of course many performance distributors come without vacuum

If this is race only, you could run completely locked.

If this is street, and you are fighting spark scatter because of the poor design of the vacuum advance system, you might be able to make this work. Here's one situation I could imagine:

You could adapt the dual pickups into a mechanical advance (locked plate) distributor, and use the proper pickup for "normal" mechanical advance only

Then you might be able to hook a relay operated by a vacuum switch that at high RPM, high vacuum, IE "easy cruise" would kick in the other pickup for more advance for cruising

CAVEAT:

I'm not sure what this will all do to "rotor phasing." Google it. This is the relationship of "when the spark happens" that is triggered by the pickup, in relation to where the rotor is at that time in the cap. The rotor MUST be reasonably lined up with the cap contacts, or you'll get loss of spark energy, damage to the cap and rotor, possible damage to the ECU, and other stuff.

MSD has some videos on this.

 

[KitCarlson]

My take is the dual pickup, was a poor fix, for Neanderthal ECU and firmware, of the lean burn era. It can be used to create a more narrow timing window of operation, to avoid errors related to the 90 degree interval of prior trigger event. However simplicity and fewer parts are often and advantage in reliability. There are better sensing solutions.

Proper dwell control using electronic means, is far superior to dual point systems. There is no need for that purpose.

If I remember my tests correctly, the difference in advance is about 40 degrees between the two sensors on a V8 distributor.

 

[KitCarlson]

I had a bit of time to put a V8 dual pickup unit on my scope for timing measurements. I measured 39.5 degrees advance, based in zero crossing timing measurements. The interval between bottom signals measures 27.8mS (90 degrees), and the advance measures 12.2mS, so it equates to 39.5 degrees. There may be a couple degrees of measurement uncertainty.

Channel 2 trace shows the timing reference, channel 1 is the secondary pickup.

While the distributor is a new old stock unit and appears clean and unused, it has problems. The signal amplitudes vary by cylinder suggesting run-out or a magnetized pickup rotor.

While a few have suggested using the secondary sensor for timing control, there may be some work involved. The 39 degrees of advance seems much. Ignition interfaces trigger near zero cross, so switching sensors may result in undesired stray ignition event.

 

[67Dart273]

Yeah, sounds like you might have to physically move the thing. If you have an engine that "likes" 40* total, that means you'd be trying to start it essentially at TDC. By the way I got the Holley TBI fired, and it will control one of the later GM HEI modules, so I ....just...might....be.....

 

[KitCarlson]

Del,

I was just providing info, the move looks necessary, and may may harder to do than the mental recreation thinking of doing it. Those that dream about a two step timing ignition, can have it their way.

As I look at the waveforms, it appears there is magnetic interaction due to using two sensors. They introduce magnetism in the reluctor (tooth wheel), that leaks into opposing pickup signals. I used a drill to rotate the distributor CW at the equivalent speed if 540 RPM, The distortion amplitudes will increase with RPM. The polarity of the distortion goes from positive to negative, so are likely rejected by the pickup interface.

It is great you got the Holley Commander going. Please let us know how it goes.