Dual Leading Ignitor Direct Fire Ignition System


1 battery
2 ignition switch
3 Leading coils
4 Leading ignitors
5 Leading magnetic pickup inside distributor
6 Trailing coil
7 Trailing ignitor
8 Trailing magnetic pickup inside distributor

Caution: If you're new to automotive electronics and don't understand your stock electronic or points ignition system, proceed no further. This article is meant for those that do. Please don't let stories of great power and driveability steer you blindly into this project. There's a real chance you could fry your car's electrical system. Get an education first before you do this project. I can't stress that enough. I can't be there to bail you out (and I'm no good at troubleshooting over the internet). You've been warned. J

I've really knocked the whole rotary ignition craze on its head with this one! No need to buy an MSD box to get direct fire, but you still get all the benefits of it, and then some. If you've already purchased an MSD and installed it, read on. This information may interest you.

This article is about offering a constructive alternative to purchasing/using the MSD on your two rotor rotary engine with an '81-'85 distributor, through the use of parts easily purchased at most junkyards/car recyclers/boneyards. You may actually already have some or all the parts you'll need to complete this mod.

If you happen to have an '80 RX-7, I cover what to look out for if choosing to stick with its early electronic distributor and ignitors a little later in this article.

If you have a points distributor, you are welcome to experiment with it, but it's best to make the switch to the later electronic unit. It's a direct drop-in replacement on most early rotaries but might require a little trimming of the AC/power steering bracket on RX-4s and Cosmos to clear the leading ignitor position. You'll quickly see what I'm talking about.

Super mega update for 2007.

What I'm presenting here is my opinion, and to my credit, several years worth of successful upgrades of previously points powered classic rotaries under my belt. I still have yet to actually install DLIDFIS on a 1st gen (the very vehicle in which the ignitors, coils and distributors came stock). Kind of a strange ironic outcome, don't you think?

So when I get the inevitable questions for how to hook up DLIDFIS in a 1st gen, I honestly can't answer the question with any kind of surety because I have not had the opportunity to try it myself first. And even if I had, I'm not very good at providing step by step instructions. What you see here is my best attempt. Pretty sad, huh?

Then again, several people have been able to follow my instructions, and with some basic understanding of electronics and their car's wiring, they cobbled together some pretty nice setups.

In the end I know it's possible for others to install DLIDFIS without any personal correspondance with me. What's more, I figured it all out on my own, without the benefit of this article or any other mention of this subject on the internet at that time.

You can imagine my frustration when these newbies come up and start asking a bunch of silly questions. We're talking basic stuff like why does the ignition key switch need to be in the circuit or which spark plugs are leading and which are trailing. Hello McFly! You seriously need to learn the basics of your STOCK ignition system first before taking on something on the order of magnitude of DLIDFIS. It's not a project for beginners. I would advise you to stop reading and go spend several hours studying everything in your engine bay. Take a day off work if that's what it takes.

Like it states elsewhere on this site, I can not be there to hand you a tool, look over your shoulder, connect the wires for you etc. All I can do is offer a comprehensive discussion of the pros and cons of rotary ignition in general, and why dual Leading sparks really are the bee's knees of rotary ignition, as well as a way to accomplish it cheaply and effectively without needing to go buy an expensive red box. In other words, all I can say is that my REPU has been running better than ever since I installed DLIDFIS (it has an '81-'85 dizzy). Once you gain an understanding of the way a rotary engine wants to run, you too can carry out even more interesting experiments than this, with everything you have learned at your disposal. Knowledge is your best friend.

On to the project.

If you've already taken the MSD plunge and are curious about DLIDFIS, the following info should be quite interesting to you. Read on.

So what is it? What makes it so good? Why don't you need to buy an MSD?

These are all the benefits I've gotten since removing my MSD DFIS (direct fire ignition system).

I've noticed that my plugs stay cleaner, my low end torque is better than it's ever been before, my secondaries feel much stronger, it starts up super quick, even when cold, and there's no need to sit in the driveway to warm it up. I just get in and go (slowly of course untill it's warmed up).

The other benefits of direct fire still apply, such as less emissions, no flat spots in the carb, more power all throughout the RPM range of the engine, a smoother idle, and it even sounds like a 2nd gen RX-7!

Here are some more reasons why DLIDFIS is so great!

1)It gives the pre-2nd gen crowd (like most of us) a good direct fire ignition system that's been proven by myself and many others to run awesome in the low end (more torque than before) and high end (past redline). Even my old truck engine is getting more high end now.

2)Each coil gets a full 12V compared to the shared voltage of SLIDFIS (the original poor man's ignition system with two coils wired in series), the shared primary and possibly secondary windings of the 2nd gen stock 'DIS style' coil, and the shared amperage of the MSD DFIS (two coils wired in parallel as per Yaw's instructions).

Note: sharing a high voltage, yet low amperage MSD CD spark hooked in parallel to two coils reduces the amperage to each coil and is not a very good idea. Yet people still do it anyway. I haven't heard of anybody hooking the MSD in series to two coils, though I tried it once as an experiment, but never ran my engine that way. Maybe it will work? I doubt it because the MSD outputs 460-480 volts and if hooked in series, it would cut that voltage in half. Conversely, the inductive breakdown of a kettering system (DLIDFIS employs this) is around 400 volts with plenty of amps (each coil gets the full amount instead of sharing it).

3)The only shared part of DLIDFIS is the pickup signal before it enters the ignitors. At first, while I had a dizzy out and studying it, I didn't know if cranking RPM would be too low to spark the ignitors so I tested it by turning the dizzy shaft slowly by hand with one and two ignitors hooked up. I could get spark at a slightly slower speed with only one ignitor hooked up. However, the shaft speed issue at cranking RPM was proven to be a non-issue. I've tested DLIDFIS on my REPU with a dead battery and if the engine still cranks, it'll still start. Thanks go to Mitsubishi for making a great product. And thanks go to Mazda for using it on the rotary!

4)The spark duration is better suited to a rotary (compared to the MSD). The longer the duration, the more AF mixture gets ignited as it moves past the plugs at a relatively high velocity. More molecules get ignited and burn more easily and fully. Read Paul Yaw's article for a good explanation.

5)You don't need a big ungainly red box under your hood. The aluminum plate I mounted my ignitors on fits nicely where an old sheetmetal box (voltage reg) used to be.

6)DLIDFIS doesn't suffer from the 8000RPM bug that so many people were experiencing with MSD DFIS. It's been run past 9000RPM without a hitch. Some people who've tried DLIDFIS have even buried their tach needle for the first time!

Note: the MSD does not suffer from the 8000RPM bug if run through the distributor, but that defeats the whole purpose and value of direct fire.

7)You can move your Trailing wires over to the Leading part of the cap to take advantage of the carbon button and only one gap to jump. All contacts inside the cap are centered. There is no offset. This is helpful. Ever look to see that the wear on the Trailing contacts is offset? But the Leading wear is still centered? After some driving with Trailing through the Leading contacts, the same offset wear marks can now be seen on the Leading contacts. There really is no difference between the two, except for a little extra width of the Leading rotor edges, and the carbon button which allows a better spark because there is only one gap to jump.

8)Timing compensation of the MSD 6A and 6AL circuitry is pre-set at the factory and is not adjustable by the user. It is different from the compensation of the J109 ignitors. This causes the Leading/Trailing split to drift as RPM rises. The prefered split of 8 (12A) or 10 (13B) ends up changing by a few degrees from idle to high RPM. I needed to readjust my timing back to 25 total advance after going to DLIDFIS, which made it easier to start. Now my timing split is rock-solid at all RPMs. I have since gone to 20L which gave me a bit more high end power without much loss in the low end.

Note: there is evidence of breaking Trailing plugs with Yaw's recommended total advance set to 25 BTDC. To be on the safe side, don't go any higher than 20L and 10T BTDC.

9)Back when I first installed an electronic distributor and my exhaust, it used to backfire quite often while decelarating, and even after I shut it off (like uncle Buck! but not nearly as loud). Most of these backfires went away when I installed SLIDFIS. Then it was about the same with the MSD DFIS, with an ocasional pop after I had been on the secondaries for a while. Now with DLIDFIS I have not gotten a single backfire, ever! Any popping I can hear are those quiet bass drum-like duhh-duhh-duhh-duhh-duhh sounds. That's a major improvement over the real popping I used to get. It doesn't pop anymore after I shut it off either. I have not touched my carb adjusting screws at all, nor have I touched my exhaust to patch up that pesky small leak in one of the welds. I did need to adjust my timing a little since I first installed the electronic dizzy, but the backfires were still happening no matter how it was set. These results are real.

10)It truly is a redundant ignition system. More on this later.

Until something better comes along that can prove itself to be truely better in all aspects, can also back up all its claims, and can be done more cheaply, I'll be sticking to DLIDFIS like stuck apex seals in a carbonated rotor! :)

You should be able to set this up in your spare time, and it may not cost you a cent depending on how many of these parts you already have laying around (most rotorheads have a few extras here and there).

The grand total of all parts needed are as follows:

A)An '81-'85 distributor (this is a given, but I'm including it anyway) or an '80 dizzy.

B)Three J109 ignitors (one for Trailing, two for Leading). You will probably only need to get one of these.

C)Three electronic ignition coils for use with a "transistor ignition" (stock Diamond coils or aftermarket, just make sure that both Leading coils match). You can use MSD blaster coils if you want, but to save money, the Diamond coils seem to work well enough (they are what I'm using).

D)Some sort of aluminum plate or heat sink that will have enough surface area to make an effective heat sink, and flat enough to make good contact with the ignitors. It needs to be drilled to fit the screw holes of the ignitors, and the section behind the pins needs to be hollowed out (with a Dremel tool or die grinder). It needs to be grounded to the chassis (check with an ohm meter after you're done fabbing the plate). I'm not sure how much mass it actually needs, but it will certainly be more than what a computer CPU needs!

E)Heat sink compound from Radio Shack Cat No. 276-1372. It comes in a 6.5 gram mini toothpaste style tube.

F)4 little quick disconnects for the pins on the backs of the ignitors.

G)A length of shielded cable which contains two conductors (like microphone XLR cable), just make sure it can handle the heat under the hood.

Update! Shielded cable is not needed! In all of my installs, I've never once used shielded cable of any kind. At first I wanted to see if I could get away without it, but as time progressed and with several vehicles running fine, I've not found any negatives to using typical 'hook up' wire as found at your local auto parts store in 14 guage and smaller thicknesses. Of course you're free to use whatever you want, but I see no need to use shielded cable. Please disregard all further references to it in this article. Thank you.

H)Some wire, various connectors to attach to the ignitors and coils, screws, nuts, drillbits, etc.

Go out and purchase these items if you need to. A local junkyard/car recycler/boneyard may have the ignitors and coils you're looking for (they're in high demand though). Radio Shack sells the mic cable in two different length spools, but I haven't tested it yet for heat resistance.

Here's how I put mine together.

I used a 5x5x1/8 inch piece of aluminum plate and drilled it to accept two J109 ignitors and hollowed out the area where the pins are with my dremel tool. Then I wiped some heat sink grease on the level flat sections on the backs of the ignitors. I used the screws left over from my old ballast resistors (correct length and included nuts) to mount the ignitors. It turned out really well. If you don't have any ballast resistors laying around, just use what ever screws/bolts/nuts are handy.

Mount the aluminum plate so it has a good ground. You could also run a wire from it to the NEG terminal of the battery if you wish (more groundz iz good groundz). I mounted mine where my old voltage regulator used to be. You might not have an external voltage reg, so just mount it somewhere convenient. My plate gets hot to the touch, but my engine/distributor housing gets hotter, so my setup should be quite reliable.

I also made a custom Trailing ignitor-to-coil harness which still uses the stock condensor on the distributor housing. Don't leave this little capacitor out of your setup. It helps with inductive kickback or RFI (my AM radio sounds fine when I'm crusin, but I've heard RFI on other older single fire setups before).

Here is a basic wiring diagram.

I used some very small quick disconnects which are made for speakers (I got these from a local car/home stereo store). They fit nicely on the pins in the backs of the ignitors. Hook the -S and +G terminals of both ignitors together in parallel (-S to -S and +G to +G), then use some shielded microphone XLR cable or something similar and run it from the plastic connector on the Leading pickup all the way down to your aluminum plate and hook it up observing correct polarity. The outer shield of the XLR cable is to prevent RFI from interfering with the relatively weak pickup signal. I don't recommend cutting the plastic thing off the pickup wires. Just poke something into it to make contact. I used a dead gutted '80 ignitor that I soldered the pickup pins to the main pins inside and used a 'T' style connector from a sub zero fluid wiring harness on the C and B terminals. Then I form fitted the aluminum backing back into the ignitor with a sheet metal hammer. It works!

The shield must be grounded at both ends. The cable must have 2 conductors inside. Even a stereo headphone cord will work, but I don't know if the insulation will handle the heat under the hood.

The coils.

You need to find a good location for both Leading coils. Some people mount them together on the strut tower because this allows shorter plug wire lengths down to the plugs. After mounting your coils, pull off the Leading wires from the cap and push them onto the coils to test if they'll reach. It doesn't matter which goes to where because they both fire at the same time. Put your old Leading coil-to-cap wire into one of your compartments behind the seat, or anywhere convenient. Just don't loose this wire! I'll tell you why a little later.

You can leave the Trailing coil where it is because it still runs through the cap, but move the wires to the Leading position. This allows the Trailing spark to make use of the carbon button and only one gap to jump under the cap. Don't worry, Trailing timing will not be changed, but the spark will be hotter! Note, you may have trouble keeping the Trailing coil in the stock coil holder if you remove the Leading coil. You might have better luck mounting the Trailing coil somewhere else, and using the stock location for both Leading coils. Or you could mount a dummy coil in the holder. It's up to you.

The wiring.

Please refer to the diagram if you need to.

Run some wires from the B terminals of the ignitors to the + terminals of the Leading coils, and the C terminals of the ignitors to the - terminals of the coils. The B and + terminals of all coils and ignitors need to be hooked to the key switch so everything turns on when the key is on. You can simplify this quite easily with jumper wires connecting all the + terminals of the coils together so they are in parallel. Leave the Trailing ignitor in its stock location on the distributor housing.

DO NOT try to use the stock harness as-is to run the Trailing ignitor output alongside the Leading pickup signal because it won't work! The black w/ white stripe wire is shared between the Leading and Trailing T connectors. They were connected together so Mazda could save a few cents per harness by reducing the amount of wires in it running over to the coils (it also saves weight and is less wear on the connections when the engine vibrates). Hey, it works great for a stock single fire system, but don't use it for DLIDFIS. That's why I recommend building a completely new harness for the Trailing ignitor and using a shielded cable for the Leading pickup. Gutting the stock harness to use the T connectors on both Leading ignitors is ok to do too. But you could always keep the stock harness intact if you ever sell the car and want to keep the DLIDFIS system for another rotary.

I personaly built a new Trailing harness and ran wires from the Leading ignitors to the coils without any T connectors so I could keep my stock harness intact. I simply used quick disconnects large enough to fit on the terminals.

Remember to hook up the little condensor mounted below and between the two vacuum diaphrams on the dizzy. It uses a bullet connector and needs to be hooked up to the main key switch lead that is connected to the B terminal on the Trailing ignitor (and is interconnected with all other B and + terminals).

Keep your tach signal wire on the - terminal of the Trailing coil.

The way you wire everything is strictly up to you. All I can do is present the basic diagram and remind you to be very careful and double check all of your wires before you apply power to them. I don't want anyone to fry a coil or ignitor.

Switch your key on (don't start the engine) and check to see that battery voltage is present on all terminals of all coils and ignitors (yes all, even on C and -). Double check everything and fire it up and see if it runs. Go for a test drive.

Now you have an ignition system that Mazda could have used but didn't because the bean counters realized that they could get away with a bare minimum instead of what's really best for the rotary. The emissions restrictions of the day weren't strict enough to justify adding one more ignitor and coil to the cost/profit margin. We can always extract more power out of our cars, and this is just one more way to do it. I'm just surprised that nobody presented this sooner (the parts have been around since 1981!).

DLIDFIS is a redundant igniton system.

If the Trailing ignitor or coil failed, the tach would quit working, and the engine would be down on power a little. It's ok to 'limp' (drive) it home in this condition. If one of the Leading ignitors or coils were to fail, it would easily be felt as a big vibration due to running on only one rotor. I don't recommend trying to drive it this way for very long. Instead, just pull over and determine if a wire came off, or whatever. Put it back on and you're on your way.

If the problem really is due to a failed Leading coil or ignitor, the reason why it was a good idea to keep your old Leading coil-to-cap wire in the car now becomes very important. This is especialy true if you decide to use J105 ignitors ('80 style, more on this later) on Leading. Keep the old wire in the car so you'll have it in an emergency! This will allow you to 'limp' home on Leading single sparks to both plugs running through the cap. It'll run just like it did with the old bone stock setup, plus you'll still have Trailing as well! Simply put all the plug and coil wires back to their old stock locations on the cap and hook the good Leading coil to the cap. Leave the dead one disconnected (you'd better unplug the dead ignitor just to be safe, but don't let the wires arc to ground). You could drive it like this for as long as needed untill getting a replacement for the part that failed. If there is no Leading ignition at all, then you either unhooked the wrong ignitor/coil (d'oh!), or there's another problem that needs attention. If the Trailing circuit is the only one still functioning, just switch the wires on the cap and it will be fine (though a little retarded). Running Trailing timing into the Leading plugs is still ok to limp home on, but at least you wont be left completely stranded.

This is the beauty of a redundant ignition system!!!!!!

A side note about the 1980 RX-7: Trailing ignition on the '80 functions only part of the time. That's why the tach signal wire is hooked to the Leading coil. It'll be a good idea to disable this option so it will run better, not to mention the fact that you'll now know if the Trailing ignition ever fails on you (by moving the tach wire to the Trailing).

The '80 style distributor already has a wiring harness that is perfect for DLIDFIS because it has long wires from the pickups over to the ignitor box on the firewall. Just rip it out and throw it on your roof (the ignitor box thing, not your dizzy!) and get yourself three '81 to '85 J109 ignitors and mount all three on an aluminum plate. I say this because the tall J105 '80 style ignitors were never very reliable. Of course you can experiment with what you already have though.

But if you happen to be a little light in the pocket book and your J105s are working fine, it's ok to use them so you only need to purchase one J109. I recommend using both J105s on Leading because they will give you balanced sparks (the advance/retard compensation will be the same which will fire both plugs at the same time, if that makes any sense). That's also why I recommend using two coils that match each other. Just use both stock coils on Leading and put the new coil on Trailing (the stock coils were made for the J105 so this is a good idea anyway, however there may be no difference between these coils and the type used in '81-'85, so you may need to find out for yourself before you proceed).

Drill the aluminum plate with two sets of bottom ignitor screw holes so it will be universal to the J105 (tall) and J109 (short) ignitors.

Otherwise if you're like the rest of us with the '81-'85 distributors, you already have 2 J109 ignitors, so all you need is one ignitor and an extra coil to complete this mod. Just leave the Trailing ignitor in place on the dizzy and get yourself one more ignitor and coil from somebody/somewhere (ask, beg, steal, don't steal, but ask nicely if the price can be lowered.)

Three J109s is the best way to go, but I'm trying to present less expensive alternatives. If you do go ahead and build a DLIDFIS system with J105s and one decides to die on you down the road, a simple swap of wires will allow you to "limp" home by running the working J105 through the cap on Leading so both plugs will fire instead of the dreaded "one rotor" problem that we've probably all felt at one point or another with dirty plugs etc. Just follow the advice above about keeping your old Leading coil-to-cap wire in case a Leading ignitor ever dies on you. A redundant ignition system and a brain full of relevant information will never leave you stranded! Try that with an MSD!

Finishing up.

When did you last check your timing and Leading/Trailing split? I recommend setting the Trailing split to 8 behind the Leading for a 12A, or 10 for a 13B. Also set the Leading to 20 total advance at 4000RPM with the vacuum advance disconnected and plugged at the manifold. It's up to you if you want to continue using vacuum advance. I don't use it. However, DO NOT plug the diaphrams on the dizzy. Let them remain open.

Thanks go to Paul Yaw for his timing and pulley marking info.

Note: One thing Paul didn't mention is that some Pullies have a little aluminum rivit that needs to be chisled off before the pulley can be removed in order to perform his pulley marking instructions. I marked my pulley, and it was very helpfull to test distributors and the Leading/Trailing split. This means you only need to perform the pulley mod once. Then use that engine to set all your other dizzies for your other rotaries! :)

Another thing I discovered recently on GSL-SE 13B pullies is an offset of 5 ATDC Leading. Trailing is still 20 which gives you a split of 15 between marks on the pulley. Be mindfull of it.

In closing...

If you've already installed an MSD, but are interested in trying DLIDFIS, go ahead and try it! You might like DLIDFIS better. I sure did!

Just to be fair, we got some basic dyno comparisons of MSD through the cap, MSD DFIS, and DLIDFIS. The MSD had more power that day. However, Geo didn't bother with any carb mixture adjustments OR resetting his timing between runs due to time and money constraints. He also was using MSD blaster2 coils which are designed specifically for the CD spark (harder for kettering ie DLIDFIS to function properly on them). Well, like I stated earlier about the compensation differences between the two ignition sources, my engine had lots more power and started easier since resetting my timing after DLIDFIS was hooked up (MSD gave me a little more power than SLIDFIS, even after all the adjustments I made, but still backfired!). Just keep that in mind.

Good luck with your project!



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