HEI and Holley Sniper compatibility?

[Mmbackpacker]

I may have made a rookie mistake...

My 77 Cherokee S NT, AMC 360/TH400...

Can I run an HEI system (the ebay "one wire hookup" special) with a Holley Sniper and MCRobb surge tank?

If no, why not, and what do I need to do?

I have been searching and running around in circles and can't seem to find a definitive answer.

Any help is really appreciated!

[Stuka]

Most of the EFI systems out there do not support HEIs due to the weak tach signal that HEI distributers output. The EFI system uses that tach signal as a cam position sensor, and if its weak, it can make the EFI act up.

We actually had a member here with Holley's previous system and it took a lot testing and working with Holley to find out it was the HEI. He swapped in a Duraspark distributer and it instantly performed better.

[tgreese]

Ya know, there is no difference in operating principle between the HEI and the Duraspark. They both make a VR (variable reluctance) signal and trigger the coil from that signal. The module and coil is packaged inside the distributor with the HEI - that's the only difference. You can mix and match components between them at will.

You can run a MSD module with the HEI by bringing the VR signal out to the MSD module, and returning the coil trigger to the HEI coil. This is all in the MSD 6A instructions. I don't see why the Holley should be any different. If it will trigger from a Duraspark, it will trigger from the HEI. Just don't use the HEI module. Bring the wires out to the Holley stuff, send the Holley wires back to the distributor. Kinda blows up the whole HEI "one wire" rationale, but it's not any different from a Duraspark in this case.

[tgreese]

https://documents.holley.com/6425.pdf

[tgreese]

Sorry I don't want to seem like a know-it-all here. Apparently neither of these systems has a dedicated tach signal, and the timing of the charge and discharge of the coil could be different. I should not claim outright that the HEI can be made to work by itself.

One solution with the HEI distributor might be some kind of active tach filter that would condition the signal so its more easily detected by the Holley TBI. Another solution might be to use the MSD module as above with either the HEI or DUraspark distributors and take the MSD tach signal for the Holley input. The Duraspark distributor will not work without a module of some kind, whether that's the Duraspark module, (compatible) HEI module, or (also compatible) MSD module.

[Mmbackpacker]

Thanks guys. Lots for me to sort out.