Ignition Education needed

[Idiocracy]

I am looking to better understand the differences between conventional and HEI distributors. I am currently running a Fitech EFI system with an HEI distributor. According to Fitech, this eliminates the ability to control timing with the EFI system. Since I am turbocharged, I REALLY need to retard timing under boost and am trying to work with what I have at the moment. I do know that I can switch to a conventional two wire dist. and let the efi do the work.

My question is if I remove the ignition module from the HEI dist. and install the MSD harness PN 8861, does that effectively convert the HEI to a conventional two wire?

Currently I am running the ignition system laid out in fig 10. If I remove the ignition module and install the harness, my thought is that I should be able to run the ignition laid out in figure 12 or 13.

I would love if someone could really get into the details of why that will or won't work.

Thanks in advance.

[turbo camino]

"HEI" is just a conventional electronic ignition system that happens to have all the usually-separate components located inside the distributor. Re-wire it however you like. Yes, you can absolutely splice in another device to control timing between the pickup and coil. Lock out all the mechanical/vacuum advance if your EFI has the ability to do a true timing curve, and not just a boost retard.

[Idiocracy]

That is what I thought. Not sure why Fitech says not to use an HEI...why not just provide the steps to so this. I have the 8861 and the 8860 (what looks to be an extension harness) on the way to wire in the EFI for timing control.

[turbo camino]

Erm... "between the pickup and coil" - maybe for clarity I should say between pickup coil and module. The wiring between module and ignition coil should stay the same, if you're keeping it that is, if your EFI doesn't have it's own coil driver(s). When you add something like a MSD box, that splices in in place of the module.

[JohnP]

Remove the HEI module.
Connect the magnetic pickup to the FiTech input trigger.
Connect the FiTech ignition output to the coil negative.

[Idiocracy]

Thats what I ended up doing. Gutted the HEI and connected the system like its a 2 wire. Thanks for the help.

[JohnP]

It would seem that you could disconnect the output of the HEI module from the coil, and instead, let it trigger an input on the FiTech.

But it's been tried before. The HEI module controls the width of its output pulse (dwell), by sensing the coil current. When the module is no longer connected to the coil, it increases the pulse width (in the now vain attempt to read some coil current) until no trigger signal is remaining, so the engine dies.

In the early '80's, both MSD and Carter carburetors tried solving this by connecting a diode from one of the magnetic pickup wires to ground. Carter said in their instructions to look for "466" on the module, as that was the only module that would work using this trick.

At the time, Carter was making the EKE, the Electronic Knock Eliminator. This was the first commercially available knock controller. It worked pretty well on a quiet engine. It was all analog, and retarded all cylinders equally. At the time, we were making a boost retard unit, and this blew us out of the water.