elwood

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I made a direct fire "distributor" many years ago, but abandoned it when I converted the car from carburetors to EFI --> https://www.rx7club.com/1st-generati...r-sale-440073/

I picked up a carbureted '84 a few years ago, and have been gradually working through the car while I drove it on a daily basis through the summers.

One of my coils would drop out after long periods at high RPM and high ambient temperature, which gave me an excuse to re-visit my direct fire experiment.

elwood

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Just as I did many years ago, I used two OEM distributors and set them up with two tiers of mag pickups. The top tier is for rotor 1, and the bottom is for rotor 2. I ground two teeth off each star wheel, 90 deg out of phase. I eliminated the vacuum advance, but kept the centrifugal advance. Split timing is adjustable with a screw in the base plate. I cut off the top of and OEM rotor cap and bonded on an aluminum cover. Lastly, I routed the magnetic signals through CAT 6 LAN cable. It has 4 stranded conductor pairs; each twisted pair is individually shielded, and the overall bundle is also shielded.

elwood

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First, I tested four J-109 ignitors, then mounted them in a remote box on the driver-side shock tower. I cut precise connector holes for each ignitor and ground the mating connectors down to fit. I used Dow Corning TC-5688 Thermal Grease between the ignitors and the box. This stuff has a thermal conductivity rating of 8.0 W/m-K, which is very good (although pricey).

The signal from the mag pickups travels through the LAN cable to the ignitor box. I used water-tight cable glands at the distributor and ignitor box to keep things dry.

The back plate is a flat piece of aluminum that also serves as a shock tower mount.

elwood

iTrader: (1)

I added two coils aft of the shock tower, and routed signal from each ignitor to its respective coil. I installed four new old stock Diamond coils and made a set of MSD 8.5mm plug wires that take the spark directly from each coil to its respective plug.

This thing fired up right away and seems to run slightly smoother than it did previously. I've driven it a few hours, and all seems well.

The one item I'll need to fix is the tach reading. Since the OEM setup calculates RPM based on the combined pulses from both trailing events, this new system causes the RPM to read half of its true value. I had the same issue with my EFI car, and I resolved it by pulling the cluster and recalibrating it.

FYI -- FB tachs are optimistic. If it tells you you're turning 8,000 RPM, the engine is really turning about 7,200.

When I recal, I'll correct this, too.

Jeff20B

iTrader: (13)

Does this no longer provide the late leading spark we've all come to associate with direct fire? My sources say no (but it's late and it's hard to get anything more than the broad strokes at this point).

TheRX7Project

iTrader: (3)

You mean the "wasted" leading spark? Looks like it does. The spinny wheel thing inside the distributor only has 2 magnetic trigger points instead of 4.

Jeff20B

iTrader: (13)

Yes, the so called wasted spark (even though on our engines it isn't actually wasted like it is on piston engines). But again my sources point to a big fat "no" here. I'd think the spinny deally would need all four points to produce a wasted spark, but then it's been years and I just woke up.

t_g_farrell

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Really nice work on all of it. As Jeff points out you lose the extra wasted spark which helps make this even better. Also if you use HEIs instead of J109s you will get a better spark as well. Something to think about.

elwood

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No, there isn't wasted spark, but it runs great. Without the wasted spark, I may be getting more dwell resulting in a hotter spark. It starts better than ever and pulls better, especially just off idle. Also, the idle raised. I was very careful to keep everything the same, and it increased 200 - 300 RPM with the same OEM timing (0 deg Leading, -20 deg Trailing).

Could be that my previous setup had issues

It would be interesting to do a back-to-back comparison vs the other options, but it would take a lot of time and effort to do the swap-over and eliminate error by using the same type coils and plug wires.

I'm aware of the HEI ignitors, but I know the J-109s were selected by Mazda for this application, and didn't want to add too many variables into the experiment. I'm also concerned about the long term durability of that combination. Has anybody run an HEI / Diamond Coil setup for high mileage?

Jeff20B

iTrader: (13)

Um, you do know the J-109s were designed for 4-tip reluctors, right? To swap one of them into your system honestly won't be stressing them beyond what they were originally designed for. Your current system, however, is only using them half as often per rev which I guess could increase their mean time before failure. Maybe. Thoughts?

As for the HEIs, I've run them here and there without issue on Diamonds. However on my main test mule, I've got classic DLIDFIS and it runs fine with boost.

t_g_farrell

iTrader: (1)

I've been running HEI for at least 4 years now, about 15,000 miles and no issues. I use TFI coils for most of it and recently switched the leading to a 2G coil so I could add trailing without needing to mount another coil somewhere. Still works great but I can tell a slight difference from the earlier setup with a TFI per plug.

Joekaistoe

It's possible that using the J-109s with 2 tip reluctors may shorten their lifespan, as they will be spending more time current-limiting power to the coils than they would in their regular application.

Just my 2 cents.

Jeff20B

iTrader: (13)

Not really. They will just think the engine is running at half the RPM of actual.

Then again, the rise and fall time of the waveform produced by the reluctor will be quicker with more of a time gap between pulses. You might be right.

sevens4me

iTrader: (1)

Mmmm...Tasty stuff here. Any chance less heat=longer lifespan? or would this setup produce more heat? just wonderin..

Jeff20B

iTrader: (13)

I just today looked at the version of this I did for a 20B many years ago. It had six pickups; three per level, with the leading set on the bottom with a stock 4 tip reluctor. This provided waste sparks which aren't actually wasted on a rotary.

The upper set of pickups were for trailing and the reluctor had only two tips. This is the only way to do it on trailing.

elwood

iTrader: (1)

Pictures?