Coil Pack Conversion - More Info Needed

[Captain Obvious]

1 hour ago, duffymahoney said:

I can control individual spark dwell with sequential.  Can you do that with wasted?  

Since two plugs are always fired in pairs, I don't think so. Out of curiosity,,, Why would you need different dwell on just cylinder #4 (for example) than all the others?

3 hours ago, Zed Head said:

the spark jumps backward for three of the plugs with wasted spark.

So I haven't thoroughly researched the name "Wasted Spark", but I always thought that the "waste" was referring to the spark on the exhaust stroke that didn't do anything. Didn't cause any harm, but it was "wasted". If that's the true origin of the name, then what you said about the spark jumping backwards doesn't have to be the case.

Granted, most of the times the wasted spark systems pair two plugs in series on the high voltage side, but I don't see any reason why you couldn't simply connect two COPs in parallel and fire them at the same time from the same low voltage source.

You wouldn't have the (cost) benefit of cutting the number of coils in half, but you could still run COP with a wasted spark system. Some people may consider the removal of the high voltage wires a benefit worth the extra cost of three more coils.

[Zed Head]

3 hours ago, Captain Obvious said:

So I haven't thoroughly researched the name "Wasted Spark", but I always thought that the "waste" was referring to the spark on the exhaust stroke that didn't do anything. Didn't cause any harm, but it was "wasted". If that's the true origin of the name, then what you said about the spark jumping backwards doesn't have to be the case.

It does if you want to use it as wasted spark.  The system pulls the spark from one plug and pushes it the other.  The direction is the same whether it's on the power stroke or the exhaust stroke.

It's pretty interesting to look at a set of plugs from a wasted spark engine.  Half of them will have the center electrode burned down and the other will have wear on the grounding strap.  It's weird.

[Mark Maras]

1 hour ago, Zed Head said:

 

It's pretty interesting to look at a set of plugs from a wasted spark engine.  Half of them will have the center electrode burned down and the other will have wear on the grounding strap.  It's weird.

 That rang a bell from the distant past. I remember an old timer telling me about condensers of different values causing either the center electrode or the ground to burn down more than the other.

[Captain Obvious]

13 hours ago, Zed Head said:

It does if you want to use it as wasted spark.  The system pulls the spark from one plug and pushes it the other.  The direction is the same whether it's on the power stroke or the exhaust stroke.

I get that. My suggestion was that you could use COP's and connect them in parallel pairs and do the same thing on the low voltage side instead of sharing a high voltage coil between two plugs. You would still be wasting a spark, but it's not the traditional "two plugs in series" circuit.

Gives you the same distributor-less function as the traditional wasted spark system, but you wouldn't get any weird electrode erosion and the energy used to fire the plug on it's exhaust stroke would not be subtracted from the plug that really matters.

Instead of "two plug in series being fed from the same coil", you could use "two coils-on-plugs in parallel being fed from the same control source".

Maybe it would be clearer if I whipped up a couple simple sketches?

[Zed Head]

It's clear.  If I recall correctly, some engines have been built with a separate mechanical distributor for each spark plug.  Mechanical COP.

Lots of ways to redescribe something.  Not sure which will help the discussion.  At least we're splitting fuel from spark, which is always important for understanding.

[Matthew Abate]

Question for @z32 fairlady: why are you considering this modification?

The reason I ask is that I am also considering it, and your answer may help me clarify my own situation. I’d like to just do this once.

Right now I have an engine being built with no ignition system at all, so anything I get will be new parts. I’m trying to make the right (for my situation) decision the first time. The new engine is an F54 block with P90A head converted to mechanical (non-hydraulic) rocket pivots, running a stage 1 cam and rebuilt SUs. I may convert to DCOE FI (Jenvey) or the like later. 

For posterity, these are the options I’ve identified so far:

• A 240z distributor (hard to find, hard to get parts, solid performance)
• A 240z distributor + Pertronix (easier to maintain, no real performance improvements)
• A ‘79 280zx distributor (requires a particular base, strait forward if you have the parts)
• A later ZX distributor (no balast resister, hotter/better spark, tach won’t work, needs a recurve, vacuum advance is “wrong”)
• Mallory Unilite (no longer manufactured, hard to find, no vac advance)
• GM or equivalent HEI distributor (available anywhere, requires machining/fabrication/module/etc.)
• 123 distributor (great performance, poor quality control, several failures documented in this forum, tunable on the fly, set and forget)
• COP + DIS (great performance particularly at high RPM, damned expensive, requires a pro to tune, clean look, as far from “period correct” as you can get)

I’ll put this question to the group: if the points distributor is on one end of the spectrum and the DIS is on the other end, how does one find the sweet spot for their car?

Edited December 1, 2019 by Matthew Abate

[siteunseen]

I bought a '79 ZX distributor as it had the best "curve" from the Excel spreadsheet floating around here.  Wired it like the atlanticz.ca Tech Tips without any issues.  Works great, tach and all.

[Zed Head]

You left out 280Z distributor + external ignition module.  GM HEI, MSD, Crane, and other modules.  Some of them are programmable.  The 280Z distributor has the variable reluctor trigger, which is very solid and dependable.   

[Matthew Abate]

1 hour ago, siteunseen said:

I bought a '79 ZX distributor as it had the best "curve" from the Excel spreadsheet floating around here.  Wired it like the atlanticz.ca Tech Tips without any issues.  Works great, tach and all.

Oh, cool. I’ll search for it.

@Zed Head, thanks for filling in the gaps!

[Matthew Abate]

@siteunseen,

This thread? 

Back to my question above: given the options I listed and the additions from @Zed Head, are there any general recommendations or categorical options?

The ‘79 distributor seems very hard to find, putting it in the same bucket as any S30 distributor. The HEI options seem interesting, but I wonder if it wouldn’t be nearly as much work/money/time to get it going as the COP/DIS options. Obviously the specific parts chosen can drive up costs, but I’d love to hear from someone who has tried a few or several options.

I know there is no “best.” Just looking for sign posts to point the way.

Edited December 1, 2019 by Matthew Abate

[LeonV]

The ZX distributor is the common go-to and a good sweet-spot between the extremes. The tach can be made to work.

[Matthew Abate]

I’ll admit that I’ve only been looking for about a week and haven’t posted a WTB in the classifieds, but so far I have not been able to find a rebuilt ‘79 at any price.

In an effort to get back on topic and make this thread helpful, here are some questions to the guys who lost the distributor:

• Why did you do it (frustration, experimenting, parts availability, etc.)?
• If you were starting from nothing and could choose anything, what would you do and why?
• Was a DIS “worth the cost” to you (someone dependent on your previous answers, I guess)?
• Are there any big flags we should be aware of before choosing the DIS path (outside of the technical details of doing it correctly)?
• Did anyone revert to a distributor? Why?

Edited December 1, 2019 by Matthew Abate