Lean burn distributor and vacuum advance distributor questions

Ark

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I'm in the process of a Fitech EFI install, and I'm thinking about what to do with the ignition system. Currently, the 5A has a standard Mopar electronic 2-wire distributor, Mopar electronic ignition box, ballast resistor, and standard canister coil. It works, sort of. I had been planning to keep this at least through the testing and tuning phase with the Fitech.

However, the Fitech ECU also includes the ability to run timing by controlling the ground side of the coil. The way this works is, you disconnect any vacuum advance, and you mechanically lock out the distributor to have zero advance at all. Then, you use a timing light to set initial timing to a spec shown in the Fitech computer, and from there a timing table in the computer controls all your timing from idle to WOT. This is, eventually, how I would like it to work.

There's a couple options for doing this, which leads to the big question:

-Buy a new MSD distributor that has screws for lockout and an adjustable coil phase.

-Buy a lockout plate from FBO, which installs into my existing distributor to disable mechanical advance. Unplug the vacuum line to disable vacuum advance.

-I have the old '87 Lean Burn distributor in a box somewhere. It is locked out from the factory because the Lean Burn computer controlled the spark.

The big question is, will there be any rotor phasing or timing issues using the lockout plate or the LB distributor? Is there a base timing offset built in to the pickup in the LB distributor? I know the early ones had two different pickups they toggled between, but the '87 should only have one. Is the pickup phased dead on with the rotor? Is there any reason it wouldn't work as well or better than locking out an advance distributor, either with a plate or via MSD's system? The goal is that the distributor basically turns into a very large crankshaft position sensor for the ECU, which perfectly describes the LB distributor, but I see a lot of people claiming it works and nobody who has actually used one in an EFI application. Does the Lean Burn distributor work the same as a locked out MSD would?
 

Mikes5thAve

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There's no reason it shouldn't work especially when one of the options is to lock out the advance on a normal distributor.
Even the ones work dual pickup you'd only use one of the pickups.
 

Ark

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There's no reason it shouldn't work especially when one of the options is to lock out the advance on a normal distributor.
Even the ones work dual pickup you'd only use one of the pickups.
What I was pondering was the specific phasing of the pickups. From my reading it sounded like the dual pickup distributors had a different, inbuilt, mechanical advance to each one. They're labeled START and RUN, so one of them presumably retards spark for starting, but I didn't know if the RUN pickup, or the single pickup in the later LB distributors, was dead on in phasing or had some built in advance or retard to it.

Kinda leaning toward the lockout plate and the regular distributor.
 

Mikes5thAve

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What I was pondering was the specific phasing of the pickups. From my reading it sounded like the dual pickup distributors had a different, inbuilt, mechanical advance to each one. They're labeled START and RUN, so one of them presumably retards spark for starting, but I didn't know if the RUN pickup, or the single pickup in the later LB distributors, was dead on in phasing or had some built in advance or retard to it.

Kinda leaning toward the lockout plate and the regular distributor.


In both the single and dual pickup distributors for the leanburn/spark/fuel control cars the pickups are mounted solidly. The only way to adjust the timing is manually turning the distributor. There's no mechanical advance to either of them.

LX-109_Front.jpg
 

Ark

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Well I've been continuing to look into this, and I don't think any factory distributor is going to work. Fitech timing control requires the adjustable rotor. Basically, you have to phase the rotor to advance the spark, and then the computer will retard it accordingly. A factory Lean Burn distributor might still run, sort of, but it's probably going to run into spark jumping issues due to the rotor not being where the computer needs it.
 

Mikes5thAve

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It would would be an interesting test. According to their youtube video they say the phasable rotor is to prevent arching at higher advance numbers which affects the timing but even with high output ignition that's a non issue with stock distributors so it must be something that has a potential to be a problem when you add fuel injection into the mix.
I see lots of posts at other forums where people say they use their stock distributor with no issues but maybe that's one of those things thst it might work fine one way but better with the proper parts? It would make you wonder more if they were pushing you to buy a distributor that they sell but that doesn't seem to be the case.
 

Ark

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It would would be an interesting test. According to their youtube video they say the phasable rotor is to prevent arching at higher advance numbers which affects the timing but even with high output ignition that's a non issue with stock distributors so it must be something that has a potential to be a problem when you add fuel injection into the mix.
I see lots of posts at other forums where people say they use their stock distributor with no issues but maybe that's one of those things thst it might work fine one way but better with the proper parts? It would make you wonder more if they were pushing you to buy a distributor that they sell but that doesn't seem to be the case.
People are using stock distributors without timing control enabled. That's the "dumb" mode which simply reads RPM off the coil and mixes fuel accordingly while the ignition system continues doing its own thing. In all my searching I haven't found anyone else using a Mopar distributor locked out with timing control. High output is a non issue with stock distributors because the mechanical and vacuum advance physically rotates and keeps the rotor phased the same. The air gap the spark jumps between the rotor and the cap terminal doesn't change as timing changes, with Fitech timing control it does.

Fitech does sell distributors but ironically not a Mopar one. Seems like 90% of people using Fitech timing control bought an MSD Pro Billet distributor to go with it.
 

Mikes5thAve

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I was seeing posts with people running the stock distributors with fitech instead of the phased rotor setup, no mention of timing control being enabled but presumably it would be since they were replies to posts with people asking if you really needed to use a different distributor or not.
There is still initial phasing with distributors that do their own advance but it's rarely an issue. It seems to only be a potential of arching in general and fitech is covering their back by recommending the phasable rotor setup rather then having people complain if it doesnt run right, plus they have no idea what someone is starting with.
For the most part I was seeing posts with some people saying they've had no problems with stock distributors and others saying with how much the setup costs to begin with its no big deal to spend a bit more on a new distributor. At least doing that everything is new and you're avoiding any potential problems.
 

Mikes5thAve

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This has me thinking- when there was a phasing problem with the MP distributors people were monkeying around with the vacuum pod to correct it and there was also a reluctor with extra slots to correct it. If you figure out how much the rotor needs to move to phase it correctly you should be able to use that to either lock a mechanical distributor in the right spot or add a slot to the reluctor to move it.. that one might be a bit hard to do. I wonder if moving the pin to the big block side moves it in the right direction to help phase it better or makes it worse?...
 
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