as discussed on the Internet Z car club.
[The Internet Z car club is an international mailing list with over 125 members and transmitted to a member's computer account over the internet.]
All information published here is the property of the original authors who are members of the IZCC and may not be reproduced for commercial purposes. Everything stated here is based on the experiences and opinions of the original authors. The authors and editor accept no responsibility for any damages arising from use of this information. Always consult your workshop manual and take appropriate precautions when working on the car. If in doubt consult a specialist.
Q:What ignition upgrades are possible for the Z ? Are the late model (260 and up) electronic ignitions adaptable to the 240Z ?
A: There are a few possibilities for upgrading the Z car ignition. The 240Z, with stock point-type ignition, are the most likely targets. Point-type ignition is old technology, and has several shortcomings for performance applications, like low spark voltage, point bounce at high RPM, and high maintenance requirements due to the mechanical nature of the system. The following sections detail some of the more popular ignition upgrades.
The Allison Electronic Ignition, available from several sources, will upgrade the point-type 240 ignition system to an electronic-type. The kit consists of a set of optical "points", or pickup-set, which mounts in the distributor instead of the mechanical point set, and the electronic control module. Installation is pretty straight forward, and requires no modifications past the installation of the aforementioned items. Allison also offers just the control modules for 260-280 applications which already have a non-point type distributor.
Because the system is optical-based, as opposed to magnetically-based, it can be susceptible to dirt which will hinder operation. When operating properly, the system provides much improved starting and overall performance due to the more precise timing provided.
The MSD (Multi-Spark Discharge) system is an electronic ignition system that discharges a series of sparks in a continuos discharge over several degrees of crank rotation. This technique provides vastly better ignition especially under marginal conditions. It makes a big difference in idle quality and low speed running. It will trigger from either points or variable reluctor pickups. The MSD-6AL contains the rev limiter. The MSD-6T comes with a shock resistant mounting kit that makes mounting the box on the firewall next to the battery very easy. The rubber stand offs let the box straddle existing wiring.
The MSD box, like most aftermarket ignitions, replaces the stock system. It takes its trigger from whatever pickup is in the distributor and fires a coil. It wires somewhat different than stock because it has a high peak current draw. A power supply lead wires directly to the battery. A "gate" signal that turns the unit on is wired to the old ignition voltage source. New wiring is installed to the distributor and coil.
One modification that must be made with the MSD system is the tachometer hook up. You must use the "tacho" output of the MSD box which is like a logic type signal. This signal, however, is too low in amplitude to trigger the Z tacho. On the early tacho that was inductively coupled to the ignition lead (pre-75), simply remove the inductive loop from the tacho and run a wire from the tacho input to the "tacho" output of the MSD box. On 75 and latter systems, remove the tacho lead and run a new lead to the "tacho" output on the MSD box. Then disassemble the tacho and find the large power resistor that is in series with the tacho input. There are typically two resistors in series with this lead. One is physically large and the other is not. Short the larger resistor by placing a jumper around it. Reassemble the tacho, install it and away you go.
Be sure to use magnetic suppression wire and not resistor wire. The peak spark current with the MSD box is on the order of 1 amp and you'll lose a volt an ohm across resistive wires. If your wires are 5000 ohms, you'll dump 5000 volts just on the wire.
The following excerpt details the steps taken with an MSD installation. The Z car in question uses a Holley carby conversion:
I selected the MS-6T model which is a medium energy model designed for circle track, NASCAR and turbocharger applications. It is ruggedised and contains an interface connector for adding a soft rev limiter. It comes with rubber mounting bushings that isolate the unit from chassis vibration.
Before installing the unit, I connected it up on the electronics bench and instrumented it. The unit does its magic by discharging about 400 volts into the coil at about 3 khz (at low rpm) for each trigger pulse. The repetition frequency and the number of pulses varies with rpm. The shift from one rep rate to another is a discrete function; the unit "shifts gears" as rpm increases. On the bench, I used an ordinary coil for sparks and a pulse generator to trigger the unit. The first observation was that at high rpm, the unit delivers enough spark energy to melt the end of the paper clip I used to establish an arc gap. The next thing I noticed was that at high rpm equivalent, the input energy was way too much for the stock coil to handle. It rather quickly heated up and started oozing oil from around the top and started bulging a bit. The MSD unit, meanwhile became only warm to the touch. An ammeter on the supply showed that the unit drew a maximum continuous current of 9 amps at about 9000 rpm equivalent. This unit puts out some serious sparks! (as a whim, I connected the MSD coil output leads to a PA loudspeaker - You should have heard the noise! Surprise! the speaker survived.)
The unit is fairly large so finding a mounting place is a chore. I started to mount it under the seat but lazed out and mounted it on the firewall in a vertical configuration just to the right of the battery. The unit comes with rubber stand off feet that hold the unit up off the A/C vacuum hoses and wiring. It was necessary to remove the cowl (where the windshield wipers come out), bore a 1.5" hole in the heater inlet baffle and then bend another baffle slightly in order to apply the nuts to the rubber stand offs. I prefer to use Rivnuts (Goodyear) but I was out of #10s. This is a very nice mounting point right next to the power source it needs. An extension cable for the trigger lead long enough to reach the 3 terminal distributor connection on the left fender well is included. I simply lifted the leads that go to the original ignition and replace them with the MSD leads. I had to extend the coil leads a bit to reach the ignition coil. The coil used is an Accel SuperCoil (highly recommended). I simply lifted the existing wires from the coil and connected the new ones. This way, I could activate the old system by reconnecting 4 wires.
I fired the engine off and the first thing I noticed was that the timing was advanced >10 degrees over what it was with the old system. A scope showed that the MSD contains a true zero-crossing detector that gives rock stable triggering. Apparently the old system triggers on the trailing slope of the reluctor output. The jitters I've always seen with a timing light and always attributed to slop in the distributor is completely gone. The timing marks are absolutely stable.
The second thing I noticed is that the timing setting has a relatively small effect on idle speed or smoothness. Apparently the extended spark duration covers up minor timing errors.
After a brief test run, I removed the spark plugs and set the gap to about 0.080" - about as wide as I dared. This made a remarkable difference. I then did my usual timing tuning of setting the timing to the most static advance that was tolerated without pinging at WOT.
With the combination of the MSD ignition and the wide plug gaps, the car has a whole new personality. IT starts instantly even after hot soaking. The slight flat spot off idle is gone. There is perceptibly more power throughout the power range but especially down low.
I followed this work up with my standard distributor modification as follows. The early Zs are limited by the quality of fuel as to the amount of static advance tolerated. And it will tolerate proportionally less centrifugal advance at WOT. Therefore the need is to increase the degree of vacuum advance and decrease the span of centrifugal advance.
The centrifugal advance is easy to handle - simply get a California model advance mechanism from the D6F4-03 distributor. This advance unit is limited to 8.3 deg advance vs. the 10 deg. of the 48 states version.
The vacuum advance requires a bit more work. The advance mechanism is adjustable but the adjustment is sealed under epoxy on the vacuum diaphragm assembly. So the first step is to pick out all of this epoxy. I use a sharpened welding rod and some leather gloves. Underneath you will find 2 concentric screws. The inner screw is a travel limit and the outer one effects a minor adjustment on the spring preload.
Before you chip out the epoxy, you will probably want to measure the default setting. You will need some form of measured vacuum and a dial indicator to measure stroke. I set the diaphragm assembly up in a vice and applied a dial indicator to the shaft. A combination hand vacuum pump and gauge purchased at PEP Boys for the purpose supplied the vacuum. Here are typical default parameters.
Start of motion: 11" hg
End of motion: 17" hg
Total motion: 0.087"
This motion produces about 7.5 degrees of distributor (14 degrees crank) advance for a manual transmission. The automatic is calibrated slightly less. See page EE-29 in the 1975 service manual.
I've found that a typically near-stock engine will benefit from as much as twice the stock vacuum advance. Therefore, I adjust the travel stop (inner) screw to allow 0.150" of travel. So the modified specs are typically:
Start of motion: 10" hg
End of motion: 21" hg
Total motion: 0.150"
A holly carburettor will never make a full 21" of vacuum on the ported vacuum line so the full advance is never realised. Nonetheless, there is more than enough advance at light throttle settings where it is really needed. The results of all these modifications are as follows:
The subjective feel of the car is great. It now has an "eagerness" to rev which stems from a greatly enhanced part throttle torque characteristic. Its off-idle torque is extremely solid without any hint of flat spots. In-Traffic performance is vastly better (an absolute MUST here in Atlanta :-) The car gained about 5" of manifold vacuum at cruise. It gained an immediate mileage increase of at least 5 mpg (measured over 2 tanks so far.) Carby retuning should improve that even more. The car willingly revs to the red line and makes useful power along the way.
I'd term the addition of the MSD system and the accompanying distributor work the second most profound thing I've done to the car behind replacing the trash SU carbs with the holly. I HIGHLY recommend this modification. The MSD ignition system can be had mail order for about $130.
Datsun used electronic distributors beginning with the '74 260Z. There is a star-like mechanism (variable reluctor) on the shaft and a pickup coil where the points used to be. When the points of the star align with the coil pole piece, the reluctance of the magnetic path is radically changed and that induces a pulse in the coil. The later model distributors are slightly larger than the points ones, a desirable property. They are cheap from salvage yards so that is the recommended course of action rather than trying to back fit a pickup to a points distributor.
The cheapest system is to get a 75 or later electronic distributor from the junkyard and use a chrysler ignition module and an Accel super coil. The diagram at the end of this article illustrates how to go about hooking it up.
For the high-RPM (>7000) or high compression racing engine these alternatives make sense. They do not make sense for any realistically streetable engine. Crank trigger uses a trigger mechanism mounted directly off the crankshaft for ignition timing. Some feel that the stock distributor, while "crank driven", can induce some sloppiness at 7000+ RPM due to the distributor shaft/gear setup used to drive the distributor from the crank. Crank trigger systems are available (I believe) from Nissan Motorsports and Electromotive.
For high compression engine builds (11:1 or better), it makes sense to use either a digital knock retard or a direct fire digital ignition. A high compression engine with tuned intake and exhaust needs less advance at high RPM and throttle where the resonances are working than it does below. A crude effort to address this are the boxes like MSD's timing computer and various mechanical high speed retard schemes.
There are a couple of good digital ignitions on the market including
Electromotive and the MOTES from Australia. The MOTES and one model of the Electromotive are actually engine management systems that also control injection but the digital ignition functionality is very good. Both use look up tables that are vectored into by engine speed and load. Both will accept knock sensor input.
Another alternative is the direct fire digital ignition construction series by Tim Drury. His system is based on a 68hc11, can trigger from a crank trigger or shaft encoder, is distributorless and uses the Motorola MC3334 intelligent coil management chip for the actual ignition trigging.
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Q:What are some common problems areas with Z car ignitions.
A: The stock Z car ignition system does not have any particular weaknesses that cause high failure rates or problems. The 240Z point ignition is prone to peculiarities resulting from the use of point technology, but these would be similar to other point-style systems. The Z car distributor cap is small, which makes it more prone to spark jumping if you are not careful about how much voltage is being sent to the cap (too high voltage resulting from non-resistive wires with non-stock coil, etc.).
Because the distributor (and hence most of the ignition circuitry) is forward mounted, it is easy to get wet, causing poor performance until it dries out. Couple that with a cracked cap, or poor sealing wires, and the problem compounds. Also, as the cars age, any and all electrical connections can be suspect, which will cause any number of ignition intermittents from partial to complete ignition loss. These problems can be especially difficult to diagnose as they may be heat, RPM, or time-intermittent, or any combination thereof.
Edited by Salman SHAMI
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