Quote:
Originally Posted by smc
Its been stated in another forum that I have a complete lack of understanding of the subject matter in regards to the coil swap. Very well. A few quick figures relating as to why I decided to do such an install.
Stock coil: 60 ma, 36,000 v maximum output with a short duration spark. $100 to $200 each.
High End Aftermarket subaru STI coils: 120ma, 50,000 v. output with modulated multi-spark capabilities. However they cost $700 for a set of 4.
My alternative: 310 ma, 51,000 v output with long duration spark. Cost, $36 each.
The remote coils are now mounted away from heat and vibration, have a more substantial spark that is less likely to be "blown out" when in a forced induction situation and are readily available and of lower cost than any alternative with a *subaru* label on them.
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Oh, I wonder who that could be.
If you are going to modify a system, it is best to know how that system works before you go changing it, or it may not be a good move.
Using separate High Energy coils, with Hi Tension leads is a retrograde step. The manufactures don’t go to the expense of fitting a coil on each plug, to be generous. They do it to solve a couple of problems that come with Hi Energy ignition. First to prevent the shorting and burning of the coil towers and leads, that happens when a separate coil, and plug wires were used. Any body that worked on GM, Ford etc, engines that used these would know the problems.
Secondly putting the coil on the plug prevented the electrical interference that Hi Energy, flowing through a wire transmits, to all the other wiring in the engine bay. With an increasing amount of analogue and digital signals, like crank sensors, airflow sensors, temp sensors, etc, which the engine relies on, this type of interference will cause increasing problems, so coil on the plug solved these.
If you are fitting different coils to this engine, they have to be the same as the originals that the ECU is set to work with. The particular coils that you have chosen have a primary resistance of 0.4 ohms; the standard coils have a primary resistance of 0.7 ohms. This means that when the ECU turns the coil on for the dwell period, a primary current of 30 amps will flow, instead of 17 amps. This current is flowed by the Ignitor till the amperage reaches about 4 amps, when the Ignitor holds it at this level till the ECU turns it off to fire the coil, due to the lower primary resistance, it will rise to this level faster, and is held at this amperage for a longer time.
This presents two problems; First the coil or the Ignitor will finally burn out from the extra current. Second, because the coil has on lower primary resistance, the rise time, to build the magnetic field will be faster, and as they don’t have a diode in the secondary to prevent the coil from firing, on the field rising, the plug will fire at the start of the dwell period and again at the end, advancing the spark.
If you and going to use different coils, the dwell period of the ECU will have to be reduced to suit the coils primary resistance, and use the diode to protect against firing on the start of the rise time. If they are used with Capacitive Discharge ignition, they can be used without the dwell change and the diode, but the wires will still be trouble.
Harvey.