Toymods Car Club Inc: Tech & Conversions => 1jz Single turbs Conversion

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KING_J
Occasional Poster

Location:
NSW
Registered:
May 2002

Re: 1jz Single turbs Conversion

Wed, 16 October 2002 01:52

Pete wrote on Tue, 15 October 2002 21:28

KingJ, fill me in!!!

I want to know if i need to fork out more dough on a MoTeC CDI unit.

I have an M800 and will be running Bosch 0227100203 ignitors x 2.
(full sequential ignition)

Will i have coil overheating problems? if i use the stock coils?

Sorry For the long post.

Well for Paul and everyone elses benefit, here is the theory behind inductive and capacitve ignitions:

The inductance and resistance of the coil will determine how quickly a coil can be charged and discharged.
A transistor (inductive igniter) is used to switch the current flow off and on in the primary coil. When the transistor is switched on, current rapidly builds from 0 to a maximum value determined by the coil inductance and resistance. This current flow induces a magnetic field within the primary. When the current is turned off, this magnetic field collapses which cuts the windings of the secondary coil and induces a high voltage surge.
The output voltage is determined by the rate of field collapse and the windings ratio between primary and secondary. Because the path to ground for the current involves the spark gap, the initial resistance is extremely high. This allows the voltage to build to a very high value until it gets high enough to jump the plug gap. The potential difference must be high enough to first ionize the gas between the electrodes. The ionized gas creates a conductive path for the current to flow. At this point, the arc jumps and current flow is established.
It is important to note that if only 10,000 volts are required to jump a plug gap under a given condition, that will be the maximum delivered. It is also important to note that the spark duration is determined by coil inductance and total resistance of the circuit. Most inductive discharge systems have a spark duration of between 1 and 2 milliseconds.
As cylinder pressure increases, the voltage required to jump the plug gap increases. This is especially true in turbocharged engines under boost. The second problem on high performance engines with high rev limits, is that there is less time to charge the coil with increasing rpm. As such, a high rpm, high output, turbo engine puts greater demands on the ignition system than does a 5000 rpm naturally aspirated engine.
The amount of time it takes to charge the coil or bring the current to maximum in the primary windings is called charge time. Input voltage and coil resistance are the main parameters relating to charge time. When the current has reached its maximum value in the primary, it is said to be fully saturated.
If current is applied longer than the time needed to fully saturate the primary, energy is wasted as heating and there is nothing more to be gained. If the current is cut off before saturation is achieved, the maximum spark energy available will be reduced.
Typical coils require charge times of between 2.1 and 6 milliseconds. Obviously, a coil requiring 6 milliseconds to saturate would be unsuitable on a high revving engine as there is not 6 milliseconds available to charge it between discharges at high rpm. For this reason, most performance and racing coils have low primary resistances between .5 and .7 ohms and are fully saturated in less than 3 milliseconds (1J coils have a primary resistance of 0.54 - 084 ohm (cold)).
Capacitive discharge ignition
CDI is used to reduce charge times. In normal inductive discharge coils, only 12-14 volts is available from the battery to charge the primary. The CDI charges capacitors to store a high voltage kick to fire to the primary side, putting between 30 and 500 volts onto the primary windings that reduces the charge time substantially. A coil that would take 3 milliseconds to become fully saturated with 12 volts is now fully saturated in less than 1 millisecond with a CDI. The same engine now will be able to turn twice the rpm and experience a major increase in cylinder pressure before encountering misfire.
An over rich or over lean condition or broken parts cannot be fixed by any CDI system.
On well tuned engines in proper repair, plug fouling is really a thing of the past.

Pete

What coil charge time are you going to run? Why did you not just use the factory igniter? The M800 will interface with the factory igniter, I can even tell you what settings you need to set the Motec ignition output waveform to if you want to run the factory igniter.

The factory igniter is a smart igniter and does not require the computer to supply it a constant charge time, just a positive edge. The Bosch 0227100203 is a dumb igniter and requires a constant charge time to be supplied by the computer.

Your set up will work, however you will find that it is not much if at all better than the factory ignition system and you will have to keep your plug gap lower than 0.8mm and may still suffer the plug fouling problem. You may as well keep the factory igniter, if you can run it sequential it will work the same. I have used those Bosch igniters on a Honda V6 with an Autronic computer before. They work OK until you start to hit big boost and big RPM. Misfire becomes a problem.

How much is the Motec CDI? The retail cost of two Bosch 0227100203s is not that much less than an Autronic CDI. If you use CDI, you will have no problems at all. Your idle will be smother than factory (I can balance a 50 cent piece on its edge on my tappet cover at idle), you will be able to run colder plugs, you will be able to run as much gap as you like (I run 1.4mm), your plugs will never foul (will last a long time if tuned correctly).

Cheers

Again, sorry for the long post

[Updated on: Wed, 16 October 2002 02:35]

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