Which distributor to use?

[clutchdust]

Sorry if this is a dupe, guys. I am trying to put together a carbureted L28 I have two different distributors and no idea how to identify which is which. I can tell you they're both magnetic to some degree, i.e. no points. I saw a thread about one of them, it appears to be a pretty popular choice. It has a plastic black box mounted at about the 11 o'clock position with a two pin connector. The other is similar but does not have any box or anything else mounted on the side. It has two magnets mounted opposite each other inside the housing. There are blue wires that come off the magnets, go through an insulator on the base of the distributor, then two of the wires are spliced and the remaining three wires are braided.

The only other thing I can tell you is that both engines were FI at one point.

I hope that's enough info to make an identification. I can't really upload any pics right now but if we can't figure this out, then I'll find some pics somewhere.

Anyway, if we can determine which is which, what distributor would be best for my carbureted engine?

[NewZed]

One sounds like a ZX distributor, or Maxima, the other like a 75-78 280Z. The centrifugal and vacuum advance curves are most likely different from each other and both different from a typical, early, carb'ed engine's stock distributor. The total centrifugal advance will be stamped on the weights (under the breaker plate) but you won't know which springs you have, so won't know when it starts and when it's all-in. If they have blue wires, they're probably rebuilt so will have a "rebuilt" vacuum advance canister, of unknown characteristics (I think that the rebuilders use conservative specs. to avoid blowing up engines). There's really not much you can tell just by looking.

 

Neither is probably ideal for your engine, but both will probably work. The 280Z dist. might be better since the ZX distributors were designed to run engines with lots of emissions controls. But the ZX distributor already has an ignition module (one reason the ZX distributor is popular, because it's easy to plug in and go if swapping from points), you'll need to get one for the 280Z distributor (the GM HEI module will work well and is cheap).

[clutchdust]

Please tell me more about the GM ignition, or point me to a thread. I would be interested in that since GM has built literally millions of vehicles that use it so parts should be cheap and available for another lifetime or two.

I think just for clarity I will pull both of them out today and post a pic.

[NewZed]

There's quite a bit of information out there on using the GM HEI module. Search the words on the internet and you'll find it. If you have original wiring you might find a specific write-up for your car, or you can figure out what the various pieces do and go from there. There are only five connections on the module to worry about, the four pins and the ground. You'll have to do the same with the ZX module, but three of the circuits are already connected internally for that one. You can use the GM module on the ZX distributor also, by removing the stock E12-80 box and rewiring.

 

If I had those two distributors and both were used, the first thing I would do is take them apart and see which one is in the best mechanical condition. Most of the old distributors are pretty well corroded inside by now. Might make your choice for you.

Edited November 3, 2012 by NewZed

[clutchdust]

So here are the two dizzies I have. Which one would be better? Street driving is really not all that big a concern, this is for my track car.

[Zark]

The one on the left looks like a 280ZX dizzy and the one on the right looks like the 260 dizzy.

 

I have a 24L with a performance cam, header, ported and polished head and polished intake manifold. I put a 280ZX dizzy in it that I got at a junk yard minus the ICM. So I went with the HEI 4 pin module which is easy to get and install. But I was not happy with its performance, it just was not stable enough. In my research on trying to make it perform better I found a very detail article on how the GM HEI 4 pin module functions. It was on a motorcycle forum. One problem is that the reluctor on the 280zx dizzy has what are called ramps ahead of the spikes. These ramps definitely play a role in form of the AC signal generated and used by the ICM to control the dwell time. The GM-HEI reluctor has simple sharp spikes on it, no ramp. The AC signal generated by the 280ZX dizzy is not the signal that the GM-HEI was designed for.

 

So I removed the GM-HEI module and put in a used Nissan e12-80 ICM. It made a big difference, much better performance through the entire rpm range. I would stick with the e12-80 module. It looks like you have the correct Nissan module on the 280ZX dizzy. If it is the e12-92 module replace it with the e12-80. I also found that with either module I needed to run a hotter plug, NGK BPR5EGP. The colder 6 would carbon foul easily.

[clutchdust]

Do you by chance have a link to that thread? I'm still really new to the different ignitions Datsun/Nissan used. In my '72, I just yanked the points and put in a Pertronix and haven't looked back.

I know either one of these distributors are pretty much the same thing as the Pertronix unit but I have no knowledge to guide me.

[NewZed]

Be careful about making decsions based on just one comment. Read all that you can find and make up your own mind. Most of what Zark has written goes against what you'll find about how the GM HEI module works and how it performs. He's interpreting motorcycle "knowledge" from one internet thread and applying it to ZX distributors. Needing a hotter plug for electronic ignition, over points, doesn't really make sense. Plug temperature choice has more to do with the combustion process and carbon buildup over time, not spark initiation. In general, Post #6 makes little sense. He might have had a real problem with the ZX distributor and the HEI module, but the reasoning behind why doesn't fit generally accepted knowledge.

 

Your biggest concern for engine performance should be the advance curves, vacuum and centrifugal. For durabilty, the condition of the distributors. Have you taken them apart yet? Tested the pickup coils' resistance? Odds are pretty good that one is broken and the choice will be made for you.

[Zark]

Here is the a link to the article. I agree with NewZed, don't make your choice based on just what I said. There are others that have recommended the e12-80 over the GM HEI for ZX distributor. I am sure you will find them. There are many internet threads by motorcycle guys concerning the using the 4-pin HEI. There area also threads on retrofitting older Chevy 235s from point to the HEI. I have a 1970 Toyota FJ-55 land cruiser that I put an HEI distributor in and it was great improvement.

 

I have tried both the GM-HEI (Pertronix and Standard) and the Nissan e12-80 on my 24L and the Nissan module makes the engine run much better. In my experience the HEI did not work well with the ZX distributor and I would not recommended.

 

http://www.scribd.com/doc/54217408/4-Pin-GM-HEI-Module-Notes

 

I agree plug temperature choice is function of the combustion process. Again what I said above about the plug choice is based on my experience. Obviously the hotter plug in my engine was fouling less.

 

Generally accepted knowledge, come on. Post #8 makes no sense.

[NewZed]

One problem is that the reluctor on the 280zx dizzy has what are called ramps ahead of the spikes. These ramps definitely play a role in form of the AC signal generated and used by the ICM to control the dwell time. The GM-HEI reluctor has simple sharp spikes on it, no ramp. The AC signal generated by the 280ZX dizzy is not the signal that the GM-HEI was designed for.

 

 

From the linked article -

 

"If a reluctor of different design is used, the dwell may end up longer or shorter than the ideal time. The HEI reluctor rotor is comprised of a wheel with short-duration spikes on it. If a rotor is used with long-duration ramps before thespikes, the bias voltage on W may increase too much, creating the aforementioned stumble at higher RPMs"

 

I have a problem sometimes, similar to what you might have done in your post, in projecting what I think might be happening in to what I write. Quite often I have to go back and remove the stuff I don't really know or add a qualifying statement.

 

I copied the the relevant passages from the articel and your post about the reasonthe ZX distributor won't work. A reference about the AC signal produced by the Zx type distributor would fill in a missing piece. I've seen that article before and noticed that the two motorcyle igntion systems described and their behavior using the HEI module don't seem to match anything I've seen described using the Z type distributor.

 

Interesting conversation. A few words or references supporting the comments about the ZX style reluctor waveform behavior, and also the "unstable" behavior that you saw using it (what do you mean by "stable" and how does it relate to the article - coil stuck on, cross-talk, or whatever) would add a lot. I'd like to know, I have a spare ZX distributor in the garage.

 

 

Edit - Ideally, we'd have something like the traces on this web page - http://jaguar.professional.org/ignition/ to work with to answer some questions. Wish i had an oscilloscope.

Edited November 25, 2012 by NewZed

[Zark]

Yep, it is easy to get carried away in writing a post and make your opinions sound too factual or set in concrete. On the other hand I suspect many are expressing opinions based on what they think is going on and I have no big problem with that.

 

I will add this. I had the HEI in first because the ZX dizzy was minus the ICM. I had a stumble from 2000 to 4000 rpm that I could not resolve and I suspect the stumble was still occurring all the way to 6,500. So after working with the carbs, coil, and timing I decided to buy the e12-80 ICM. I also tried it with and without the vacuum advance. I got a used Nissan ICM from a Z restoration shop in Escondido, CA. It is a simple thing to switch between the two ICMs. I left the HEI in so I could switch back and forth between the two. The e12-80 just made it run much better by the butt-o-meter and the idle was smoother. I still had a slight stumble with the e12-80 so I decided to try the hotter plug and since then It is running great, smooth acceleration through the whole range. I feel ready for the hill climbs I skipped this summer. To complete the picture I need to describe the engine better.

• Original 24L rebuilt and balanced
  
• E88 head ported and polished
  
• Intake manifold smoothed and polished to 120 grit
  
• Comp cam with a 260 grind, running about 3.5 degrees advanced at 0.050" open on the intake valve
  
• MSA 3-2 header
  
• Original SUs with thinner needles recommended by Dave at Z-therapy, can't recall the letter designation
  

Now maybe the HEI would work better in a stock set up. My oldest son is an electrical engineer with just two terms to graduation and he does have a real nice tetronix scope. Since I have the HEI running in my old cruiser and the e12-80 in the Z I should get him to compare the AC signals from both distributors. Of course my two boys want me to start over with mega squirt and injectors or better yet six motorcycle carbs. Ugh.

[NewZed]

That would be pretty cool to see, just to gain a little more insight in to what works and why. Thanks for taking my post in a positive way, you could have told me to get stuffed and went away.

 

Just to round out the picture a little bit, what type of coil were/are you using and what is its primary circuit resistance? I think that HEI module is designed for a sub-one ohm coil, about 0.4-0.5, from various internet sources. Could be a factor, maybe. The ZX coil is 0.84 - 1.02 according to the FSM.

 

For the record, I'm using an HEI module with a Z31 coil (~one ohm primary, 10K secondary), with a 280Z style single position pickup coil (not the stator ring), and it works great.

 

Another odd thing - the GM HEI stator looks like the ZX style stator, ring-shaped, just eight points instead of six. If you were just eye-balling parts, you'd probably pick the ZX style distributor instead of the 280Z style as the one that would work right.

 

 

To the OP - if the ZX distributor is in good shape it would probably be the easiest to install. Fewer wires to mess with, just power and coil negative. Then you can measure your advance characteristics while the engine is running, and decide if you need to make any changes. That's another post though.

[clutchdust]

 

 

 

To the OP - if the ZX distributor is in good shape it would probably be the easiest to install. Fewer wires to mess with, just power and coil negative. Then you can measure your advance characteristics while the engine is running, and decide if you need to make any changes. That's another post though.

Not really. Sounds exactly like what I was asking. Just this once, pretend I don't know jack about Datsun distributors and walk me through which one I should use and what parts are needed.

[NewZed]

This link should help you out - http://atlanticz.ca/zclub/techtips/distributor/index.html

[Zark]

We will put the oscope on the HEI and ZX distributors to analyze the signals to the ICM and post the results here. It will have to wait until Christmas break.

 

I was using a coil with 0.4 ohm primary resistance with the HEI and I am still using it with the e12-80.

 

I also ran 10 gauge wire from just behind the ignition switch through the tack and to the coil to reduce the voltage drop. To make the tack work I formed a new loop of #10 wire to replace the much smaller gauge white wire that is the loop on the original harness. I just laid the white loop to the side. I used spade connectors on the little #10 loop because it would have been very difficult to form the loop in a continuous piece of #10 wire. Previously we had done other repairs to the tach to make it work. I suspect the weak link in the tach are the two transistors. If you have a problem with the tack I might be able to help.

[clutchdust]

So I think I've decided to go with the one on the left (e12-80?). I have a bunch of modules and bits and pieces I don't even know what they go to. Does this distributor use a separate module? Or is this (+) to one side and (-) to the other side and done? Also, what is the distributor on the right? What parts (if any) does it need to work? I will be listing that one on my F/S thread.