Lean-Burn Dual P/U Distributors - Any Good?

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Mtrhed

Mtrhed

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Hello all,
I'm wanting to make some decisions about components for an ignition system in my 440 powered '68 Dart. The car came with a few parts so I have options. The system in the car is a factory magnetic P/U distributor with a gold box (?) and ballast resistor. The car came with a couple of non vacuum Uni-Lites as well but in my experiance these units are fragile so I think I'll verify that they work then sell them on eBay. The car also came with two Mallory # 685 boxes. These seem to have more features than a standard Hy-Fire VI an look like they've never been hooked up. My initial plan is to have the OE distributor recurved and run one of the Mallory boxes.
I've noticed that some of the late 70's Lean-burn distributors had no vacuum advance but did have dual magnetic pickups. Has any one used these in a performance application? In the future I'm tempted to try fuel injection with ignition control. Im not sure if the second pick-up is just retarded from the first or if it's placed to emulate a signal from the cam like Mallorys Dual-Sync units. Please share your coments and opinions on these items with me. Thanks for your time!
 
the 2nd pickup is just to retard it. no adv springs I believe. would likely be good for a simple trigger. What I'd do is dial in your 70's OE dist subsytems in order: initial/total/spring/vac can (if used) with an HEI module and an E coil or a parts house 4 in ECU and a ballast and a coil/ballast combo that has at least 1.5 ohms total between the two. wiring a 4 terminal "dual" ballast together (adding a blue wire loop on both ends "OE has the blue loop on one end") will drop the ohms to 1.1 (on the last one I did) which is very close to what you'd need depending on your coil selection
 
About three years ago I purchased a NOS (new old stock) lean burn distributor for evaluation. I captured the waveforms using a dual channel scope. The results were not good. My understanding differs from RapidRobert, not to say I am correct.

The Mopar pickup coils are biased by a magnets, the reluctor tooth draws away magnetic flux resulting in change of voltage at pickup leads. The addition of the second sightly corrupts the primary pickup signal. Also note the deviation in signal magnitude for adjacent cycles.
View attachment IMG_0664 (800x586).jpg

My measurements suggest the second sensor leads the primary by about 40 degrees. I have a good guess why, but just a guess so keeping my mouth shut.

In general variable reluctance sensors are not used as position sensors. This is because the amplitude varies with angular velocity (RPM), this alters the reference position because it is sensed by an analog comparator of fixed amplitude.

Below are waveforms of a VR trigger circuit. The bottom digital signal going from high to low is the trigger point. With proper design of reluctor and trigger the second pickup could have been eliminated. Mopar was often economic driven in a way, disturbing rational development of electronics.
View attachment IMG_0593 (1024x740).jpg
To make greater improvements the A Hall sensor could have been incorporated, and it was a few years later on the 2.2L mopar 4. I have heard of a Hall tab wheel for the V8, but have not confirmed that. I have seen the 1/2 circle used as phase sensor, use in conjunction with flexplate tone wheel and Hall sensor. That choice would let you do coil on plug, eliminating the rotor.
 
I guess one partial "answer" is eliminate the pickup you are not using.
 
AJ/FormS said:
Mtrhed
I had thoughts like yours one time. I think the MS efi system can use that dizzy
Click to expand...

Sure can. Honestly that's a good starter setup. I did a coil near plug/logic coil conversion with my MS3 EFI. really, really nice


KitCarlson said:
About three years ago I purchased a NOS (new old stock) lean burn distributor for evaluation. I captured the waveforms using a dual channel scope. The results were not good. My understanding differs from RapidRobert, not to say I am correct.

The Mopar pickup coils are biased by a magnets, the reluctor tooth draws away magnetic flux resulting in change of voltage at pickup leads. The addition of the second sightly corrupts the primary pickup signal. Also note the deviation in signal magnitude for adjacent cycles.
View attachment 1714851947

My measurements suggest the second sensor leads the primary by about 40 degrees. I have a good guess why, but just a guess so keeping my mouth shut.

In general variable reluctance sensors are not used as position sensors. This is because the amplitude varies with angular velocity (RPM), this alters the reference position because it is sensed by an analog comparator of fixed amplitude.

Below are waveforms of a VR trigger circuit. The bottom digital signal going from high to low is the trigger point. With proper design of reluctor and trigger the second pickup could have been eliminated. Mopar was often economic driven in a way, disturbing rational development of electronics.
View attachment 1714851948
To make greater improvements the A Hall sensor could have been incorporated, and it was a few years later on the 2.2L mopar 4. I have heard of a Hall tab wheel for the V8, but have not confirmed that. I have seen the 1/2 circle used as phase sensor, use in conjunction with flexplate tone wheel and Hall sensor. That choice would let you do coil on plug, eliminating the rotor.
Click to expand...

Right, they're typically speed sensors, HOWEVER, you can do position by having a known missing tooth when you have enough teeth. The MS3 System I installed uses basically a 1990's-2000's Ford 36-1 setup that uses a VR sensor. The angle between tooth #1 (first after the tooth) is known in the computer AND you have a second sensor (the dodge magnum distributor is a hall switch), which allows you to have positions for sequential injection. You wouldn't have to have a hall switch.




The VR sensors are far more reliable, and you really don't have to worry about adding extra parts like pull-up resistors.

You also can't use this as a dual sync distributor. If you want EFI, you can do spark timing with a distributor like this (I suggest an 80's electronic spark control single pickup over this one), or you do a 36-1 or 60-2 wheel with the 90's 3.9/5.2/5.9 distributor as a cam sensor.
 
Thanks everyone for all the great ideas. Rapid Robert might have put the final nail in this idea for now. I've never seen one of these units in the flesh and didn't know the timing was locked out on them. The Mallory 685 is smarter then the average box but doesn't have the juice to provide complete timing control. FI will be way down the road for me. I've spotted a batch of Mallory Dual Sync distributors on that auction site for $100. These seem too cheap to be true. I'm a little leary of Mallory at this point since they're a dead issue and replacement parts thru MSD are so expensive. For now I'm leaning towards of putting a nice curve in a stock single pick-up magnetic distributor and run it with a 685 box with an E-core coil. I'll pick up a simular distributor, have it curved, and convert it to run a GM HEI module. I'll leave this unit wrapped up in a spare-parts box in the trunk in case the 685 box goes out. I've been tempted to get one of the off-shore billet distributors that are so comonn now but whenever I asked about replacement parts beyond a cap & rotor nobody will return a message.
 
The megasquirt site has much info on spark controls. I think the late 70's - 80's Mopar distributor had no centrifugal or vacuum advance. That was all done in the "spark computer" or "lean burn" controller. The vacuum sensor was built onto the side of the box and looked like a vac advance pod. My 82 Aries had that, but the distributor pickup was a Hall-effect type.

The easiest computer approach is a GM 8-pin HEI module, controlled by a Holley Commander 950 controller (or similar) from an rpm, Pman map. You can add a knock sensor & module for optimal control. Steal it from the same 85-95 GM V-8 truck and screw it in as your block plug.

The "final solution" in my 65 Dart 273 will be just like goldduster318. I already mounted a 36-1 toothed wheel on my crank pulley w/ Ford VR pickup and also made a mount for a Chrysler Hall-effect pickup, both off the lower water pump bolts (posted photos several years ago). A Ford EDIS module will process the 36-1 signal. It normally drives Ford coil packs in a "wasted spark" system, but any two 4-cyl coil packs would also work. But I plan to do like above and use the cam sensor in a Magnum distributor w/ custom logic circuit to select just the needed spark for each cylinder and drive GM truck LS coils. I have all the parts but no time, but then I'm not even driving that car yet.
 
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